1
|
Reserva RL, Micompal MTMM, Mendoza KC, Confesor MNP. Excitable dynamics of Physarum polycephalum plasmodial nodes under chemotaxis. Biochem Biophys Res Commun 2021; 550:171-176. [PMID: 33743354 DOI: 10.1016/j.bbrc.2021.02.133] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/15/2021] [Accepted: 02/25/2021] [Indexed: 11/30/2022]
Abstract
Recent results show that the chemotactic response of uni-cellular decentralized systems such as amoeboid and mammalian cells, is excitable. The same observation has not yet been reported for multi-nucleated decentralized biological systems. Here we present experimental results that shows the Physarum polycephalum plasmodial nodes spatio-temporal chemotactic dynamics as an excitable response. We found a highly optimized signal synthesis method wherein the Physarum nodes employ two intensity thresholds to properly navigate the chemoattractant field and generate corresponding spike dynamics in the node count. The node spike dynamics was found to correspond to the polarized-depolarized transition in the Physarum polycephalum morphology. Validation of our experimental observations via Brownian lattice simulations yields the same quantitative results with our experiments.
Collapse
Affiliation(s)
- Rosario L Reserva
- Department of Physics and Complex Systems Group - PRISM, MSU-Iligan Institute of Technology, Tibanga, Iligan City, 9200, Philippines
| | - Maria Theresa Mae M Micompal
- Department of Physics and Complex Systems Group - PRISM, MSU-Iligan Institute of Technology, Tibanga, Iligan City, 9200, Philippines
| | - Kathleen C Mendoza
- Department of Physics and Complex Systems Group - PRISM, MSU-Iligan Institute of Technology, Tibanga, Iligan City, 9200, Philippines
| | - Mark Nolan P Confesor
- Department of Physics and Complex Systems Group - PRISM, MSU-Iligan Institute of Technology, Tibanga, Iligan City, 9200, Philippines.
| |
Collapse
|
2
|
Karmakar R. State of the art of bacterial chemotaxis. J Basic Microbiol 2021; 61:366-379. [PMID: 33687766 DOI: 10.1002/jobm.202000661] [Citation(s) in RCA: 39] [Impact Index Per Article: 13.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/05/2020] [Revised: 02/09/2021] [Accepted: 02/25/2021] [Indexed: 12/13/2022]
Abstract
Bacterial chemotaxis is a biased movement of bacteria toward the beneficial chemical gradient or away from a toxic chemical gradient. This movement is achieved by sensing a chemical gradient by chemoreceptors. In most of the chemotaxis studies, Escherichia coli has been used as a model organism. E. coli have about 4-6 flagella on their surfaces, and the motility is achieved by rotating the flagella. Each flagellum has reversible flagellar motors at its base, which rotate the flagella in counterclockwise and clockwise directions to achieve "run" and "tumble." The chemotaxis of bacteria is regulated by a network of interacting proteins. The sensory signal is processed and transmitted to the flagellar motor by cytoplasmic proteins. Bacterial chemotaxis plays an important role in many biological processes such as biofilm formation, quorum sensing, bacterial pathogenesis, and host infection. Bacterial chemotaxis can be applied for bioremediation, horizontal gene transfer, drug delivery, or maybe some other industry in near future. This review contains an overview of bacterial chemotaxis, recent findings of the physiological importance of bacterial chemotaxis in other biological processes, and the application of bacterial chemotaxis.
Collapse
Affiliation(s)
- Richa Karmakar
- Department of Physics, University of California San Diego, La Jolla, California, USA
| |
Collapse
|
3
|
Ma L, Wu Y, Li Y, Aazmi A, Zhou H, Zhang B, Yang H. Current Advances on 3D-Bioprinted Liver Tissue Models. Adv Healthc Mater 2020; 9:e2001517. [PMID: 33073522 DOI: 10.1002/adhm.202001517] [Citation(s) in RCA: 45] [Impact Index Per Article: 11.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/25/2020] [Revised: 09/27/2020] [Indexed: 12/16/2022]
Abstract
The liver, the largest gland in the human body, plays a key role in metabolism, bile production, detoxification, and water and electrolyte regulation. The toxins or drugs that the gastrointestinal system absorbs reach the liver first before entering the bloodstream. Liver disease is one of the leading causes of death worldwide. Therefore, an in vitro liver tissue model that reproduces the main functions of the liver can be a reliable platform for investigating liver diseases and developing new drugs. In addition, the limitations in traditional, planar monolayer cell cultures and animal tests for evaluating the toxicity and efficacy of drug candidates can be overcome. Currently, the newly emerging 3D bioprinting technologies have the ability to construct in vitro liver tissue models both in static scaffolds and dynamic liver-on-chip manners. This review mainly focuses on the construction and applications of liver tissue models based on 3D bioprinting. Special attention is given to 3D bioprinting strategies and bioinks for constructing liver tissue models including the cell sources and hydrogel selection. In addition, the main advantages and limitations and the major challenges and future perspectives are discussed, paving the way for the next generation of in vitro liver tissue models.
Collapse
Affiliation(s)
- Liang Ma
- State Key Laboratory of Fluid Power and Mechatronic Systems Zhejiang University Hangzhou 310027 P. R. China
- School of Mechanical Engineering Zhejiang University Hangzhou 310027 P. R. China
| | - Yutong Wu
- State Key Laboratory of Fluid Power and Mechatronic Systems Zhejiang University Hangzhou 310027 P. R. China
- School of Mechanical Engineering Zhejiang University Hangzhou 310027 P. R. China
| | - Yuting Li
- State Key Laboratory of Fluid Power and Mechatronic Systems Zhejiang University Hangzhou 310027 P. R. China
- School of Mechanical Engineering Zhejiang University Hangzhou 310027 P. R. China
| | - Abdellah Aazmi
- State Key Laboratory of Fluid Power and Mechatronic Systems Zhejiang University Hangzhou 310027 P. R. China
- School of Mechanical Engineering Zhejiang University Hangzhou 310027 P. R. China
| | - Hongzhao Zhou
- State Key Laboratory of Fluid Power and Mechatronic Systems Zhejiang University Hangzhou 310027 P. R. China
- School of Mechanical Engineering Zhejiang University Hangzhou 310027 P. R. China
| | - Bin Zhang
- State Key Laboratory of Fluid Power and Mechatronic Systems Zhejiang University Hangzhou 310027 P. R. China
- School of Mechanical Engineering Zhejiang University Hangzhou 310027 P. R. China
| | - Huayong Yang
- State Key Laboratory of Fluid Power and Mechatronic Systems Zhejiang University Hangzhou 310027 P. R. China
- School of Mechanical Engineering Zhejiang University Hangzhou 310027 P. R. China
| |
Collapse
|
4
|
Hosseini V, Maroufi NF, Saghati S, Asadi N, Darabi M, Ahmad SNS, Hosseinkhani H, Rahbarghazi R. Current progress in hepatic tissue regeneration by tissue engineering. J Transl Med 2019; 17:383. [PMID: 31752920 PMCID: PMC6873477 DOI: 10.1186/s12967-019-02137-6] [Citation(s) in RCA: 55] [Impact Index Per Article: 11.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2019] [Accepted: 11/12/2019] [Indexed: 12/12/2022] Open
Abstract
Liver, as a vital organ, is responsible for a wide range of biological functions to maintain homeostasis and any type of damages to hepatic tissue contributes to disease progression and death. Viral infection, trauma, carcinoma, alcohol misuse and inborn errors of metabolism are common causes of liver diseases are a severe known reason for leading to end-stage liver disease or liver failure. In either way, liver transplantation is the only treatment option which is, however, hampered by the increasing scarcity of organ donor. Over the past years, considerable efforts have been directed toward liver regeneration aiming at developing new approaches and methodologies to enhance the transplantation process. These approaches include producing decellularized scaffolds from the liver organ, 3D bio-printing system, and nano-based 3D scaffolds to simulate the native liver microenvironment. The application of small molecules and micro-RNAs and genetic manipulation in favor of hepatic differentiation of distinct stem cells could also be exploited. All of these strategies will help to facilitate the application of stem cells in human medicine. This article reviews the most recent strategies to generate a high amount of mature hepatocyte-like cells and updates current knowledge on liver regenerative medicine.
Collapse
Affiliation(s)
- Vahid Hosseini
- Stem Cell Research Center, Tabriz University of Medical Sciences, Imam Reza St., Golgasht St., Tabriz, 5166614756, Iran.,Department of Biochemistry and Clinical Laboratories, Faculty of Medicine, Tabriz University of Medical Sciences, Tabriz, Iran
| | - Nazila Fathi Maroufi
- Department of Biochemistry and Clinical Laboratories, Faculty of Medicine, Tabriz University of Medical Sciences, Tabriz, Iran.,Student Research Committee, Tabriz University of Medical Sciences, Tabriz, Iran
| | - Sepideh Saghati
- Department of Tissue Engineering, Faculty of Advanced Medical Sciences, Tabriz University of Medical Sciences, Tabriz, Iran
| | - Nahideh Asadi
- Department of Nanotechnology, Faculty of Advanced Medical Sciences, Tabriz University of Medical Sciences, Tabriz, Iran
| | - Masoud Darabi
- Stem Cell Research Center, Tabriz University of Medical Sciences, Imam Reza St., Golgasht St., Tabriz, 5166614756, Iran.,Department of Biochemistry and Clinical Laboratories, Faculty of Medicine, Tabriz University of Medical Sciences, Tabriz, Iran
| | - Saeed Nazari Soltan Ahmad
- Department of Biochemistry and Clinical Laboratories, Faculty of Medicine, Tabriz University of Medical Sciences, Tabriz, Iran
| | | | - Reza Rahbarghazi
- Department of Applied Cell Sciences, Faculty of Advanced Medical Sciences, Tabriz University of Medical Sciences, Tabriz, Iran.
| |
Collapse
|
5
|
Muok AR, Briegel A, Crane BR. Regulation of the chemotaxis histidine kinase CheA: A structural perspective. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2019; 1862:183030. [PMID: 31374212 DOI: 10.1016/j.bbamem.2019.183030] [Citation(s) in RCA: 16] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/30/2019] [Revised: 07/24/2019] [Accepted: 07/25/2019] [Indexed: 02/06/2023]
Abstract
Bacteria sense and respond to their environment through a highly conserved assembly of transmembrane chemoreceptors (MCPs), the histidine kinase CheA, and the coupling protein CheW, hereafter termed "the chemosensory array". In recent years, great strides have been made in understanding the architecture of the chemosensory array and how this assembly engenders sensitive and cooperative responses. Nonetheless, a central outstanding question surrounds how receptors modulate the activity of the CheA kinase, the enzymatic output of the sensory system. With a focus on recent advances, we summarize the current understanding of array structure and function to comment on the molecular mechanism by which CheA, receptors and CheW generate the high sensitivity, gain and dynamic range emblematic of bacterial chemotaxis. The complexity of the chemosensory arrays has motivated investigation with many different approaches. In particular, structural methods, genetics, cellular activity assays, nanodisc technology and cryo-electron tomography have provided advances that bridge length scales and connect molecular mechanism to cellular function. Given the high degree of component integration in the chemosensory arrays, we ultimately aim to understand how such networked molecular interactions generate a whole that is truly greater than the sum of its parts. This article is part of a Special Issue entitled: Molecular biophysics of membranes and membrane proteins.
Collapse
Affiliation(s)
- Alise R Muok
- Institute for Biology, Leiden University, Sylviusweg 72, 2333 BE Leiden, the Netherlands
| | - Ariane Briegel
- Institute for Biology, Leiden University, Sylviusweg 72, 2333 BE Leiden, the Netherlands
| | - Brian R Crane
- Department of Chemistry and Chemical Biology, Cornell University, Ithaca, NY 14850, United States of America.
| |
Collapse
|
6
|
Brewin RJW, Brewin TG, Phillips J, Rose S, Abdulaziz A, Wimmer W, Sathyendranath S, Platt T. A Printable Device for Measuring Clarity and Colour in Lake and Nearshore Waters. SENSORS 2019; 19:s19040936. [PMID: 30813342 PMCID: PMC6413171 DOI: 10.3390/s19040936] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 01/14/2019] [Revised: 02/07/2019] [Accepted: 02/15/2019] [Indexed: 11/28/2022]
Abstract
Two expanding areas of science and technology are citizen science and three-dimensional (3D) printing. Citizen science has a proven capability to generate reliable data and contribute to unexpected scientific discovery. It can put science into the hands of the citizens, increasing understanding, promoting environmental stewardship, and leading to the production of large databases for use in environmental monitoring. 3D printing has the potential to create cheap, bespoke scientific instruments that have formerly required dedicated facilities to assemble. It can put instrument manufacturing into the hands of any citizen who has access to a 3D printer. In this paper, we present a simple hand-held device designed to measure the Secchi depth and water colour (Forel Ule scale) of lake, estuarine and nearshore regions. The device is manufactured with marine resistant materials (mostly biodegradable) using a 3D printer and basic workshop tools. It is inexpensive to manufacture, lightweight, easy to use, and accessible to a wide range of users. It builds on a long tradition in optical limnology and oceanography, but is modified for ease of operation in smaller water bodies, and from small watercraft and platforms. We provide detailed instructions on how to build the device and highlight examples of its use for scientific education, citizen science, satellite validation of ocean colour data, and low-cost monitoring of water clarity, colour and temperature.
Collapse
Affiliation(s)
- Robert J W Brewin
- Plymouth Marine Laboratory, Plymouth, Devon PL1 3DH, UK.
- National Centre for Earth Observation, Plymouth Marine Laboratory, Plymouth, Devon PL1 3DH, UK.
| | - Thomas G Brewin
- Chatham and Clarendon Grammar School, Ramsgate, Kent CT11 9BB, UK.
| | - Joseph Phillips
- Chatham and Clarendon Grammar School, Ramsgate, Kent CT11 9BB, UK.
- Faculty of Science and Technology, Bournemouth University, Bournemouth, Dorset BH12 5BB, UK.
| | - Sophie Rose
- Chatham and Clarendon Grammar School, Ramsgate, Kent CT11 9BB, UK.
- Faculty of Science and Technology, Bournemouth University, Bournemouth, Dorset BH12 5BB, UK.
| | - Anas Abdulaziz
- CSIR-National Institute of Oceanography, Regional Centre Kochi, Kerala 682018, India.
| | - Werenfrid Wimmer
- Ocean and Earth Science, National Oceanography Centre Southampton, University of Southampton, Southampton, Hampshire SO14 3ZH, UK.
| | - Shubha Sathyendranath
- Plymouth Marine Laboratory, Plymouth, Devon PL1 3DH, UK.
- National Centre for Earth Observation, Plymouth Marine Laboratory, Plymouth, Devon PL1 3DH, UK.
| | - Trevor Platt
- Plymouth Marine Laboratory, Plymouth, Devon PL1 3DH, UK.
| |
Collapse
|
7
|
Kim Y, Kang K, Yoon S, Kim JS, Park SA, Kim WD, Lee SB, Ryu KY, Jeong J, Choi D. Prolongation of liver-specific function for primary hepatocytes maintenance in 3D printed architectures. Organogenesis 2018; 14:1-12. [PMID: 29359998 DOI: 10.1080/15476278.2018.1423931] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
Isolated primary hepatocytes from the liver are very similar to in vivo native liver hepatocytes, but they have the disadvantage of a limited lifespan in 2D culture. Although a sandwich culture and 3D organoids with mesenchymal stem cells (MSCs) as an attractive assistant cell source to extend lifespan can be used, it cannot fully reproduce the in vivo architecture. Moreover, long-term 3D culture leads to cell death because of hypoxic stress. Therefore, to overcome the drawback of 2D and 3D organoids, we try to use a 3D printing technique using alginate hydrogels with primary hepatocytes and MSCs. The viability of isolated hepatocytes was more than 90%, and the cells remained alive for 7 days without morphological changes in the 3D hepatic architecture with MSCs. Compared to a 2D system, the expression level of functional hepatic genes and proteins was higher for up to 7 days in the 3D hepatic architecture. These results suggest that both the 3D bio-printing technique and paracrine molecules secreted by MSCs supported long-term culture of hepatocytes without morphological changes. Thus, this technique allows for widespread expansion of cells while forming multicellular aggregates, may be applied to drug screening and could be an efficient method for developing an artificial liver.
Collapse
Affiliation(s)
- Yohan Kim
- a Department of Translational Medicine , Graduate School of Biomedical Science and Engineering, Hanyang University , Seoul , Republic of Korea.,b HY Indang Center of Regenerative Medicine and Stem Cell Research, Hanyang University , Seoul , Republic of Korea.,c Department of Surgery , Hanyang University College of Medicine , Seoul , Republic of Korea
| | - Kyojin Kang
- a Department of Translational Medicine , Graduate School of Biomedical Science and Engineering, Hanyang University , Seoul , Republic of Korea.,b HY Indang Center of Regenerative Medicine and Stem Cell Research, Hanyang University , Seoul , Republic of Korea.,c Department of Surgery , Hanyang University College of Medicine , Seoul , Republic of Korea
| | - Sangtae Yoon
- a Department of Translational Medicine , Graduate School of Biomedical Science and Engineering, Hanyang University , Seoul , Republic of Korea.,b HY Indang Center of Regenerative Medicine and Stem Cell Research, Hanyang University , Seoul , Republic of Korea.,c Department of Surgery , Hanyang University College of Medicine , Seoul , Republic of Korea
| | - Ji Sook Kim
- d Department of Pathology , Hanyang University College of Medicine , Seoul , Republic of Korea
| | - Su A Park
- e Department of Nature-Inspired Nanoconvergence Systems , Korea Institute of Machinery and Materials , Daejeon , Republic of Korea
| | - Wan Doo Kim
- e Department of Nature-Inspired Nanoconvergence Systems , Korea Institute of Machinery and Materials , Daejeon , Republic of Korea
| | - Seung Bum Lee
- f Laboratory of Radiation Exposure & Therapeutics, National Radiation Emergency Medical Center, Korea Institute of Radiological & Medical Science (KIRAMS) , Seoul , Republic of Korea
| | - Ki-Young Ryu
- g Department of Obstetrics and Gynecology, Hanyang University College of Medicine , Seoul , Korea
| | - Jaemin Jeong
- b HY Indang Center of Regenerative Medicine and Stem Cell Research, Hanyang University , Seoul , Republic of Korea.,c Department of Surgery , Hanyang University College of Medicine , Seoul , Republic of Korea
| | - Dongho Choi
- a Department of Translational Medicine , Graduate School of Biomedical Science and Engineering, Hanyang University , Seoul , Republic of Korea.,b HY Indang Center of Regenerative Medicine and Stem Cell Research, Hanyang University , Seoul , Republic of Korea.,c Department of Surgery , Hanyang University College of Medicine , Seoul , Republic of Korea
| |
Collapse
|
8
|
Abstract
Most motile bacteria follow spatial gradients of chemical and physical stimuli in their environment. In Escherichia coli and other bacteria, the best characterized chemotaxis is in gradients of amino acids or sugars, but other physiological stimuli such as pH, osmolarity, redox potentials, and temperature are also known to elicit tactic responses. These multiple environmental stimuli are integrated and processed within a highly sophisticated chemotaxis network to generate coordinated chemotaxis behavior, which features high sensitivity, a wide dynamic range, and robustness against variations in background stimulation, protein levels, and temperature. Although early studies relied on behavioral analyses to characterize chemotactic responses in vivo, or on biochemical assays to study the pathway in vitro, we describe here a method to directly measure the intracellular pathway response using Förster resonance energy transfer (FRET). In E. coli, the most commonly used form of the FRET assay relies on the interaction between the phosphorylated response regulator CheY and its phosphatase CheZ to quantify activity of the histidine kinase CheA. We further describe a FRET assay for Bacillus subtilis, which employs CheY and the motor-associated phosphatase FliY as a FRET pair. In particular, we highlight the use of FRET to quantify pathway properties, including signal amplification, dynamic range, and kinetics of adaptation.
Collapse
Affiliation(s)
- Anja Paulick
- Max Planck Institute for Terrestrial Microbiology, Marburg, Germany
- LOEWE Research Center for Synthetic Microbiology (SYNMIKRO), Marburg, Germany
| | - Victor Sourjik
- Max Planck Institute for Terrestrial Microbiology, Marburg, Germany.
- LOEWE Research Center for Synthetic Microbiology (SYNMIKRO), Marburg, Germany.
| |
Collapse
|
9
|
Jeon H, Kang K, Park SA, Kim WD, Paik SS, Lee SH, Jeong J, Choi D. Generation of Multilayered 3D Structures of HepG2 Cells Using a Bio-printing Technique. Gut Liver 2017; 11:121-128. [PMID: 27559001 PMCID: PMC5221869 DOI: 10.5009/gnl16010] [Citation(s) in RCA: 64] [Impact Index Per Article: 9.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/04/2016] [Revised: 03/13/2016] [Accepted: 03/13/2016] [Indexed: 12/27/2022] Open
Abstract
Background/Aims Chronic liver disease is a major widespread cause of death, and whole liver transplantation is the only definitive treatment for patients with end-stage liver diseases. However, many problems, including donor shortage, surgical complications and cost, hinder their usage. Recently, tissue-engineering technology provided a potential breakthrough for solving these problems. Three-dimensional (3D) printing technology has been used to mimic tissues and organs suitable for transplantation, but applications for the liver have been rare. Methods A 3D bioprinting system was used to construct 3D printed hepatic structures using alginate. HepG2 cells were cultured on these 3D structures for 3 weeks and examined by fluorescence microscopy, histology and immunohistochemistry. The expression of liver-specific markers was quantified on days 1, 7, 14, and 21. Results The cells grew well on the alginate scaffold, and liver-specific gene expression increased. The cells grew more extensively in 3D culture than two-dimensional culture and exhibited better structural aspects of the liver, indicating that the 3D bioprinting method recapitulates the liver architecture. Conclusions The 3D bioprinting of hepatic structures appears feasible. This technology may become a major tool and provide a bridge between basic science and the clinical challenges for regenerative medicine of the liver.
Collapse
Affiliation(s)
- Hyeryeon Jeon
- Department of Surgery, Hanyang University College of Medicine, Seoul, Korea
| | - Kyojin Kang
- Department of Surgery, Hanyang University College of Medicine, Seoul, Korea
| | - Su A Park
- Department of Nature-Inspired Nano Convergence Systems, Korea Institute of Machinery and Materials, Daejeon, Korea
| | - Wan Doo Kim
- Department of Nature-Inspired Nano Convergence Systems, Korea Institute of Machinery and Materials, Daejeon, Korea
| | - Seung Sam Paik
- Department of Pathology, Hanyang University College of Medicine, Seoul, Korea
| | - Sang-Hun Lee
- Department of Biomedical Science, Graduate School of Biomedical Science Engineering, Hanyang University, Seoul, Korea
| | - Jaemin Jeong
- Department of Surgery, Hanyang University College of Medicine, Seoul, Korea
| | - Dongho Choi
- Department of Surgery, Hanyang University College of Medicine, Seoul, Korea
| |
Collapse
|
10
|
|
11
|
Ortega DR, Zhulin IB. Evolutionary Genomics Suggests That CheV Is an Additional Adaptor for Accommodating Specific Chemoreceptors within the Chemotaxis Signaling Complex. PLoS Comput Biol 2016; 12:e1004723. [PMID: 26844549 PMCID: PMC4742279 DOI: 10.1371/journal.pcbi.1004723] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/06/2015] [Accepted: 12/29/2015] [Indexed: 12/30/2022] Open
Abstract
Escherichia coli and Salmonella enterica are models for many experiments in molecular biology including chemotaxis, and most of the results obtained with one organism have been generalized to another. While most components of the chemotaxis pathway are strongly conserved between the two species, Salmonella genomes contain some chemoreceptors and an additional protein, CheV, that are not found in E. coli. The role of CheV was examined in distantly related species Bacillus subtilis and Helicobacter pylori, but its role in bacterial chemotaxis is still not well understood. We tested a hypothesis that in enterobacteria CheV functions as an additional adaptor linking the CheA kinase to certain types of chemoreceptors that cannot be effectively accommodated by the universal adaptor CheW. Phylogenetic profiling, genomic context and comparative protein sequence analyses suggested that CheV interacts with specific domains of CheA and chemoreceptors from an orthologous group exemplified by the Salmonella McpC protein. Structural consideration of the conservation patterns suggests that CheV and CheW share the same binding spot on the chemoreceptor structure, but have some affinity bias towards chemoreceptors from different orthologous groups. Finally, published experimental results and data newly obtained via comparative genomics support the idea that CheV functions as a “phosphate sink” possibly to off-set the over-stimulation of the kinase by certain types of chemoreceptors. Overall, our results strongly suggest that CheV is an additional adaptor for accommodating specific chemoreceptors within the chemotaxis signaling complex. Due to the overwhelming complexity and diversity of biological systems, the functional roles of the majority of proteins encoded in sequenced genomes remain unknown or poorly understood. The multi-protein pathway controlling chemotaxis in bacteria and archaea is an example of such complexity and diversity. Chemotaxis pathway in E. coli is one of the best understood signal transduction networks in nature; however, this model organism lacks some of the system components, such as CheV, that are found in many other species. The biological role of CheV is still under avid debate. CheV is an auxiliary component of many chemotaxis systems and is present in important human pathogens, such as Salmonella and Helicobacter, where chemotaxis is being studied as an important virulence trait. Here we established the evolutionary history of the chemotaxis pathway in enterobacteria and combined a computational genomics approach with available structural information to propose a role for CheV. Our results show that CheV in enterics evolved as an adaptor for a specific type of chemoreceptors. Furthermore, we propose that some CheV-associated chemoreceptors might increase the kinase activity above the base level, and in these cases CheV acts as an attenuator.
Collapse
Affiliation(s)
- Davi R. Ortega
- Computer Science and Mathematics Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States of America
- Department of Microbiology, University of Tennessee, Knoxville, Tennessee, United States of America
| | - Igor B. Zhulin
- Computer Science and Mathematics Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States of America
- Department of Microbiology, University of Tennessee, Knoxville, Tennessee, United States of America
- * E-mail:
| |
Collapse
|
12
|
Oikonomou C, Swulius M, Briegel A, Beeby M, Yao Q, Chang YW, Jensen G. Electron cryotomography. METHODS IN MICROBIOLOGY 2016. [DOI: 10.1016/bs.mim.2016.10.001] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
|
13
|
Eismann S, Endres RG. Protein Connectivity in Chemotaxis Receptor Complexes. PLoS Comput Biol 2015; 11:e1004650. [PMID: 26646441 PMCID: PMC4672929 DOI: 10.1371/journal.pcbi.1004650] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/09/2015] [Accepted: 11/10/2015] [Indexed: 01/09/2023] Open
Abstract
The chemotaxis sensory system allows bacteria such as Escherichia coli to swim towards nutrients and away from repellents. The underlying pathway is remarkably sensitive in detecting chemical gradients over a wide range of ambient concentrations. Interactions among receptors, which are predominantly clustered at the cell poles, are crucial to this sensitivity. Although it has been suggested that the kinase CheA and the adapter protein CheW are integral for receptor connectivity, the exact coupling mechanism remains unclear. Here, we present a statistical-mechanics approach to model the receptor linkage mechanism itself, building on nanodisc and electron cryotomography experiments. Specifically, we investigate how the sensing behavior of mixed receptor clusters is affected by variations in the expression levels of CheA and CheW at a constant receptor density in the membrane. Our model compares favorably with dose-response curves from in vivo Förster resonance energy transfer (FRET) measurements, demonstrating that the receptor-methylation level has only minor effects on receptor cooperativity. Importantly, our model provides an explanation for the non-intuitive conclusion that the receptor cooperativity decreases with increasing levels of CheA, a core signaling protein associated with the receptors, whereas the receptor cooperativity increases with increasing levels of CheW, a key adapter protein. Finally, we propose an evolutionary advantage as explanation for the recently suggested CheW-only linker structures. Receptor clusters of the bacterial chemotaxis sensory system act as antennae to amplify tiny changes in concentrations in the chemical environment of the cell, ultimately steering the cell towards nutrients and away from toxins. Despite bacterial chemotaxis being the most widely studied sensory pathway, the exact architecture of the receptor clusters remains speculative, with understanding suffering from a number of paradoxical observations. To address these issues with respect to the protein arrangement in the linkers connecting receptors, we present a statistical-mechanics model that combines insights from electron cryotomography on the linker architecture with results from fluorescence imaging of signaling in living cells. Although the signaling data for different expression levels of key molecular components in the linkers seems contradictory at first, our model reconciles these predictions with structural and biochemical data. Finally, we provide an evolutionary explanation for the observation that some of the incorporated linkers do not seem to transmit signals from the receptors.
Collapse
Affiliation(s)
- Stephan Eismann
- Department of Physics and Astronomy, University of Heidelberg, Heidelberg, Germany
- Department of Life Sciences and Centre for Integrative Systems Biology and Bioinformatics, Imperial College London, London, United Kingdom
| | - Robert G. Endres
- Department of Life Sciences and Centre for Integrative Systems Biology and Bioinformatics, Imperial College London, London, United Kingdom
- * E-mail:
| |
Collapse
|
14
|
Greenswag AR, Muok A, Li X, Crane BR. Conformational Transitions that Enable Histidine Kinase Autophosphorylation and Receptor Array Integration. J Mol Biol 2015; 427:3890-907. [PMID: 26522934 PMCID: PMC4721237 DOI: 10.1016/j.jmb.2015.10.015] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/09/2015] [Revised: 10/15/2015] [Accepted: 10/18/2015] [Indexed: 01/07/2023]
Abstract
During bacterial chemotaxis, transmembrane chemoreceptor arrays regulate autophosphorylation of the dimeric histidine kinase CheA. The five domains of CheA (P1-P5) each play a specific role in coupling receptor stimulation to CheA activity. Biochemical and X-ray scattering studies of thermostable CheA from Thermotoga maritima determine that the His-containing substrate domain (P1) is sequestered by interactions that depend upon P1 of the adjacent subunit. Non-hydrolyzable ATP analogs (but not ATP or ADP) release P1 from the protein core (domains P3P4P5) and increase its mobility. Detachment of both P1 domains or removal of one within a dimer increases net autophosphorylation substantially at physiological temperature (55°C). However, nearly all activity is lost without the dimerization domain (P3). The linker length between P1 and P3 dictates intersubunit (trans) versus intrasubunit (cis) autophosphorylation, with the trans reaction requiring a minimum length of 47 residues. A new crystal structure of the most active dimerization-plus-kinase unit (P3P4) reveals trans directing interactions between the tether connecting P3 to P2-P1 and the adjacent ATP-binding (P4) domain. The orientation of P4 relative to P3 in the P3P4 structure supports a planar CheA conformation that is required by membrane array models, and it suggests that the ATP lid of CheA may be poised to interact with receptors and coupling proteins. Collectively, these data suggest that the P1 domains are restrained in the off-state as a result of cross-subunit interactions. Perturbations at the nucleotide-binding pocket increase P1 mobility and access of the substrate His to P4-bound ATP.
Collapse
|
15
|
3D bioprinting of tissues and organs. Nat Biotechnol 2015; 32:773-85. [PMID: 25093879 DOI: 10.1038/nbt.2958] [Citation(s) in RCA: 3305] [Impact Index Per Article: 367.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/05/2013] [Accepted: 06/12/2014] [Indexed: 02/07/2023]
Abstract
Additive manufacturing, otherwise known as three-dimensional (3D) printing, is driving major innovations in many areas, such as engineering, manufacturing, art, education and medicine. Recent advances have enabled 3D printing of biocompatible materials, cells and supporting components into complex 3D functional living tissues. 3D bioprinting is being applied to regenerative medicine to address the need for tissues and organs suitable for transplantation. Compared with non-biological printing, 3D bioprinting involves additional complexities, such as the choice of materials, cell types, growth and differentiation factors, and technical challenges related to the sensitivities of living cells and the construction of tissues. Addressing these complexities requires the integration of technologies from the fields of engineering, biomaterials science, cell biology, physics and medicine. 3D bioprinting has already been used for the generation and transplantation of several tissues, including multilayered skin, bone, vascular grafts, tracheal splints, heart tissue and cartilaginous structures. Other applications include developing high-throughput 3D-bioprinted tissue models for research, drug discovery and toxicology.
Collapse
|
16
|
Zamparo M, Chianale F, Tebaldi C, Cosentino-Lagomarsino M, Nicodemi M, Gamba A. Dynamic membrane patterning, signal localization and polarity in living cells. SOFT MATTER 2015; 11:838-849. [PMID: 25563791 DOI: 10.1039/c4sm02157f] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
We review the molecular and physical aspects of the dynamic localization of signaling molecules on the plasma membranes of living cells. At the nanoscale, clusters of receptors and signaling proteins play an essential role in the processing of extracellular signals. At the microscale, "soft" and highly dynamic signaling domains control the interaction of individual cells with their environment. At the multicellular scale, individual polarity patterns control the forces that shape multicellular aggregates and tissues.
Collapse
Affiliation(s)
- M Zamparo
- Human Genetics Foundation - Torino, Italy.
| | | | | | | | | | | |
Collapse
|
17
|
A phenylalanine rotameric switch for signal-state control in bacterial chemoreceptors. Nat Commun 2014; 4:2881. [PMID: 24335957 DOI: 10.1038/ncomms3881] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/15/2013] [Accepted: 11/07/2013] [Indexed: 11/08/2022] Open
Abstract
Bacterial chemoreceptors are widely used as a model system for elucidating the molecular mechanisms of transmembrane signalling and have provided a detailed understanding of how ligand binding by the receptor modulates the activity of its associated kinase CheA. However, the mechanisms by which conformational signals move between signalling elements within a receptor dimer and how they control kinase activity remain unknown. Here, using long molecular dynamics simulations, we show that the kinase-activating cytoplasmic tip of the chemoreceptor fluctuates between two stable conformations in a signal-dependent manner. A highly conserved residue, Phe396, appears to serve as the conformational switch, because flipping of the stacked aromatic rings of an interacting F396-F396' pair in the receptor homodimer takes place concomitantly with the signal-related conformational changes. We suggest that interacting aromatic residues, which are common stabilizers of protein tertiary structure, might serve as rotameric molecular switches in other biological processes as well.
Collapse
|
18
|
|
19
|
Abstract
Allostery is the most direct and efficient way for regulation of biological macromolecule function, ranging from the control of metabolic mechanisms to signal transduction pathways. Allosteric modulators target to allosteric sites, offering distinct advantages compared to orthosteric ligands that target to active sites, such as greater specificity, reduced side effects, and lower toxicity. Allosteric modulators have therefore drawn increasing attention as potential therapeutic drugs in the design and development of new drugs. In recent years, advancements in our understanding of the fundamental principles underlying allostery, coupled with the exploitation of powerful techniques and methods in the field of allostery, provide unprecedented opportunities to discover allosteric proteins, detect and characterize allosteric sites, design and develop novel efficient allosteric drugs, and recapitulate the universal features of allosteric proteins and allosteric modulators. In the present review, we summarize the recent advances in the repertoire of allostery, with a particular focus on the aforementioned allosteric compounds.
Collapse
Affiliation(s)
- Shaoyong Lu
- Department of Pathophysiology, Chemical Biology Division of Shanghai Universities E-Institutes, Key Laboratory of Cell Differentiation and Apoptosis of Chinese Ministry of Education, Shanghai Jiao-Tong University School of Medicine (SJTU-SM), Shanghai, China
| | | | | |
Collapse
|
20
|
Santos TMA, Lin TY, Rajendran M, Anderson SM, Weibel DB. Polar localization of Escherichia coli chemoreceptors requires an intact Tol-Pal complex. Mol Microbiol 2014; 92:985-1004. [PMID: 24720726 DOI: 10.1111/mmi.12609] [Citation(s) in RCA: 42] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 04/05/2014] [Indexed: 11/29/2022]
Abstract
Subcellular biomolecular localization is critical for the metabolic and structural properties of the cell. The functional implications of the spatiotemporal distribution of protein complexes during the bacterial cell cycle have long been acknowledged; however, the molecular mechanisms for generating and maintaining their dynamic localization in bacteria are not completely understood. Here we demonstrate that the trans-envelope Tol-Pal complex, a widely conserved component of the cell envelope of Gram-negative bacteria, is required to maintain the polar positioning of chemoreceptor clusters in Escherichia coli. Localization of the chemoreceptors was independent of phospholipid composition of the membrane and the curvature of the cell wall. Instead, our data indicate that chemoreceptors interact with components of the Tol-Pal complex and that this interaction is required to polarly localize chemoreceptor clusters. We found that disruption of the Tol-Pal complex perturbs the polar localization of chemoreceptors, alters cell motility, and affects chemotaxis. We propose that the E. coli Tol-Pal complex restricts mobility of the chemoreceptor clusters at the cell poles and may be involved in regulatory mechanisms that co-ordinate cell division and segregation of the chemosensory machinery.
Collapse
Affiliation(s)
- Thiago M A Santos
- Department of Biochemistry, University of Wisconsin-Madison, 440 Henry Mall, Madison, WI, 53706, USA
| | | | | | | | | |
Collapse
|
21
|
Changeux JP. 50 years of allosteric interactions: the twists and turns of the models. Nat Rev Mol Cell Biol 2013; 14:819-29. [DOI: 10.1038/nrm3695] [Citation(s) in RCA: 117] [Impact Index Per Article: 10.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
|
22
|
Changeux JP. The concept of allosteric interaction and its consequences for the chemistry of the brain. J Biol Chem 2013; 288:26969-26986. [PMID: 23878193 DOI: 10.1074/jbc.x113.503375] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Throughout this Reflections article, I have tried to follow up on the genesis in the 1960s and subsequent evolution of the concept of allosteric interaction and to examine its consequences within the past decades, essentially in the field of the neuroscience. The main conclusion is that allosteric mechanisms built on similar structural principles operate in bacterial regulatory enzymes, gene repressors (and the related nuclear receptors), rhodopsin, G-protein-coupled receptors, neurotransmitter receptors, ion channels, and so on from prokaryotes up to the human brain yet with important features of their own. Thus, future research on these basic cybernetic sensors is expected to develop in two major directions: at the elementary level, toward the atomic structure and molecular dynamics of the conformational changes involved in signal recognition and transduction, but also at a higher level of organization, the contribution of allosteric mechanisms to the modulation of brain functions.
Collapse
Affiliation(s)
- Jean-Pierre Changeux
- Collège de France, 75005 Paris and the Institut Pasteur, 75724 Paris Cedex 15, France.
| |
Collapse
|
23
|
Changeux JP. The Origins of Allostery: From Personal Memories to Material for the Future. J Mol Biol 2013; 425:1396-406. [DOI: 10.1016/j.jmb.2013.02.033] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/19/2013] [Accepted: 02/20/2013] [Indexed: 11/16/2022]
|
24
|
Frank V, Vaknin A. Prolonged stimuli alter the bacterial chemosensory clusters. Mol Microbiol 2013; 88:634-44. [PMID: 23551504 DOI: 10.1111/mmi.12215] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 03/21/2013] [Indexed: 11/27/2022]
Abstract
The clustering of membrane-bound receptors plays an essential role in various biological systems. A notable model system for studying this phenomenon is the bacterial chemosensory cluster that allows motile bacteria to navigate along chemical gradients in their environment. While the basic structure of these chemosensory clusters is becoming clear, their dynamic nature and operation are not yet understood. By measuring the fluorescence polarization of tagged receptor clusters in live Escherichia coli cells, we provide evidence for stimulus-induced dynamics in these sensory clusters. We find that when a stimulus is applied, the packing of the receptors slowly decreases and that the process reverses when the stimulus is removed. Consistent with these physical changes we find that the effective cooperativity of the kinase response slowly evolves in the presence of a stimulus. Time-lapse fluorescence imaging indicates that, despite these changes, the receptor clusters do not generally dissociate upon ligand binding. These data reveal stimulus-dependent plasticity in chemoreceptor clusters.
Collapse
Affiliation(s)
- Vered Frank
- The Racah Institute of Physics, The Hebrew University, Jerusalem, 91904, Israel
| | | |
Collapse
|
25
|
The propagation of allosteric states in large multiprotein complexes. J Mol Biol 2012; 425:1410-4. [PMID: 23274139 DOI: 10.1016/j.jmb.2012.12.008] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2012] [Revised: 12/11/2012] [Accepted: 12/16/2012] [Indexed: 11/21/2022]
Abstract
A statistical view of allostery leads to a more nuanced and physically realistic picture of protein cooperativity. If the conformational state of one protein molecule in a multiprotein complex influences the probability of a particular conformation in a neighbouring protein, then changes can propagate. Given suitable parameters, linear or two-dimensional arrays of allosteric subunits will then behave similar to an Ising model, exhibiting hypersharp responses to external conditions. Predictions based on this concept find good quantitative agreement in a number of experimental systems including switching of the bacterial flagellar motor, amplification of ligand signals in the Escherichia coli chemotaxis receptors, and termination of calcium sparks in cardiac muscle. A similar mechanism could potentially provide a universal mechanism of integration within living cells.
Collapse
|
26
|
Bhatnagar J, Sircar R, Borbat PP, Freed JH, Crane BR. Self-association of the histidine kinase CheA as studied by pulsed dipolar ESR spectroscopy. Biophys J 2012; 102:2192-201. [PMID: 22824284 DOI: 10.1016/j.bpj.2012.03.038] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/09/2011] [Revised: 02/29/2012] [Accepted: 03/12/2012] [Indexed: 11/26/2022] Open
Abstract
Biologically important protein complexes often involve molecular interactions that are low affinity or transient. We apply pulsed dipolar electron spin resonance spectroscopy and site-directed spin labeling in what to our knowledge is a new approach to study aggregation and to identify regions on protein surfaces that participate in weak, but specific molecular interactions. As a test case, we have probed the self-association of the chemotaxis kinase CheA, which forms signaling clusters with chemoreceptors and the coupling protein CheW at the poles of bacterial cells. By measuring the intermolecular dipolar interactions sensed by spin-labels distributed over the protein surface, we show that the soluble CheA kinase aggregates to a small extent through interactions mediated by its regulatory (P5) domain. Direct dipolar distance measurements confirm that a hydrophobic surface at the periphery of P5 subdomain 2 associates CheA dimers in solution. This result is further supported by differential disulfide cross-linking from engineered cysteine reporter sites. We suggest that the periphery of P5 is an interaction site on CheA for other similar hydrophobic surfaces and plays an important role in structuring the signaling particle.
Collapse
Affiliation(s)
- Jaya Bhatnagar
- Advanced Center for ESR Studies (ACERT), Cornell University, Ithaca, NY, USA
| | | | | | | | | |
Collapse
|
27
|
Hall BA, Armitage JP, Sansom MSP. Mechanism of bacterial signal transduction revealed by molecular dynamics of Tsr dimers and trimers of dimers in lipid vesicles. PLoS Comput Biol 2012; 8:e1002685. [PMID: 23028283 PMCID: PMC3447960 DOI: 10.1371/journal.pcbi.1002685] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/16/2012] [Accepted: 07/22/2012] [Indexed: 02/02/2023] Open
Abstract
Bacterial chemoreceptors provide an important model for understanding signalling processes. In the serine receptor Tsr from E. coli, a binding event in the periplasmic domain of the receptor dimer causes a shift in a single transmembrane helix of roughly 0.15 nm towards the cytoplasm. This small change is propagated through the ∼22 nm length of the receptor, causing downstream inhibition of the kinase CheA. This requires interactions within a trimer of receptor dimers. Additionally, the signal is amplified across a 53,000 nm2 array of chemoreceptor proteins, including ∼5,200 receptor trimers-of-dimers, at the cell pole. Despite a wealth of experimental data on the system, including high resolution structures of individual domains and extensive mutagenesis data, it remains uncertain how information is communicated across the receptor from the binding event to the downstream effectors. We present a molecular model of the entire Tsr dimer, and examine its behaviour using coarse-grained molecular dynamics and elastic network modelling. We observe a large bending in dimer models between the linker domain HAMP and coiled-coil domains, which is supported by experimental data. Models of the trimer of dimers, built from the dimer models, are more constrained and likely represent the signalling state. Simulations of the models in a 70 nm diameter vesicle with a biologically realistic lipid mixture reveal specific lipid interactions and oligomerisation of the trimer of dimers. The results indicate a mechanism whereby small motions of a single helix can be amplified through HAMP domain packing, to initiate large changes in the whole receptor structure. To understand cell signalling events requires a physical model of the structure and behaviour of the signalling proteins involved. The methyl-accepting chemoreceptor proteins direct bacterial movement towards food sources and away from toxins. Based on experimental data we have built structural models of the serine chemoreceptor (Tsr) as a dimer, which is incapable of activating the downstream kinase CheA, and as a trimer of dimers, which can activate CheA. We have performed molecular dynamics simulation to reveal the behaviour of these two forms in a planar lipid bilayer and in a 70 nm diameter lipid vesicle with a mixture of lipids mimicking the E. coli inner membrane. We show that in isolation the dimers undergo a bending movement around the central HAMP domain, whereas the trimer-of-dimers model does not. Comparison with published experimental data suggests that these bending motions are real, and that they occur in the trimer of dimers only in response to ligand binding. Drawing together these observations with studies showing that the signalling event involves small piston motions in the transmembrane helices suggests that the bending motion is frustrated in the unliganded trimer of dimers, and that ligand binding induces bending by repacking the HAMP interface.
Collapse
Affiliation(s)
| | | | - Mark S. P. Sansom
- Oxford Centre for Integrative Systems Biology, Department of Biochemistry, University of Oxford, Oxford, United Kingdom
- * E-mail:
| |
Collapse
|
28
|
State of the art in silico tools for the study of signaling pathways in cancer. Int J Mol Sci 2012; 13:6561-6581. [PMID: 22837650 PMCID: PMC3397482 DOI: 10.3390/ijms13066561] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/27/2012] [Revised: 05/03/2012] [Accepted: 05/10/2012] [Indexed: 12/18/2022] Open
Abstract
In the last several years, researchers have exhibited an intense interest in the evolutionarily conserved signaling pathways that have crucial roles during embryonic development. Interestingly, the malfunctioning of these signaling pathways leads to several human diseases, including cancer. The chemical and biophysical events that occur during cellular signaling, as well as the number of interactions within a signaling pathway, make these systems complex to study. In silico resources are tools used to aid the understanding of cellular signaling pathways. Systems approaches have provided a deeper knowledge of diverse biochemical processes, including individual metabolic pathways, signaling networks and genome-scale metabolic networks. In the future, these tools will be enormously valuable, if they continue to be developed in parallel with growing biological knowledge. In this study, an overview of the bioinformatics resources that are currently available for the analysis of biological networks is provided.
Collapse
|
29
|
Molecular architecture of chemoreceptor arrays revealed by cryoelectron tomography of Escherichia coli minicells. Proc Natl Acad Sci U S A 2012; 109:E1481-8. [PMID: 22556268 DOI: 10.1073/pnas.1200781109] [Citation(s) in RCA: 150] [Impact Index Per Article: 12.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022] Open
Abstract
The chemoreceptors of Escherichia coli localize to the cell poles and form a highly ordered array in concert with the CheA kinase and the CheW coupling factor. However, a high-resolution structure of the array has been lacking, and the molecular basis of array assembly has thus remained elusive. Here, we use cryoelectron tomography of flagellated E. coli minicells to derive a 3D map of the intact array. Docking of high-resolution structures into the 3D map provides a model of the core signaling complex, in which a CheA/CheW dimer bridges two adjacent receptor trimers via multiple hydrophobic interactions. A further, hitherto unknown, hydrophobic interaction between CheW and the homologous P5 domain of CheA in an adjacent core complex connects the complexes into an extended array. This architecture provides a structural basis for array formation and could explain the high sensitivity and cooperativity of chemotaxis signaling in E. coli.
Collapse
|
30
|
Abstract
Bacterial cells utilize three-dimensional (3D) protein assemblies to perform important cellular functions such as growth, division, chemoreception, and motility. These assemblies are composed of mechanoproteins that can mechanically deform and exert force. Sometimes, small-nucleotide hydrolysis is coupled to mechanical deformations. In this review, we describe the general principle for an understanding of the coupling of mechanics with chemistry in mechanochemical systems. We apply this principle to understand bacterial cell shape and morphogenesis and how mechanical forces can influence peptidoglycan cell wall growth. We review a model that can potentially reconcile the growth dynamics of the cell wall with the role of cytoskeletal proteins such as MreB and crescentin. We also review the application of mechanochemical principles to understand the assembly and constriction of the FtsZ ring. A number of potential mechanisms are proposed, and important questions are discussed.
Collapse
|
31
|
Abstract
The Monod-Wyman-Changeux (MWC) model was conceived in 1965 to account for the signal transduction and cooperative properties of bacterial regulatory enzymes and hemoglobin. It was soon extended to pharmacological receptors for neurotransmitters and other macromolecular entities involved in intracellular and intercellular communications. Five decades later, the two main hypotheses of the model are reexamined on the basis of a variety of regulatory proteins with known X-ray structures: (a) Regulatory proteins possess an oligomeric structure with symmetry properties, and (b) the allosteric interactions between topographically distinct sites are mediated by a conformational transition established between a few preestablished states with conservation of symmetry and ligand-directed conformational selection. Several well-documented examples are adequately represented by the MWC model, yet a few possible exceptions are noted. New questions are raised concerning the dynamics of the allosteric transitions and more complex supramolecular ensembles.
Collapse
Affiliation(s)
- Jean-Pierre Changeux
- Collège de France & Institut Pasteur, URA CNRS 2182, Paris Cedex 15 75724, France.
| |
Collapse
|
32
|
Frank V, Koler M, Furst S, Vaknin A. The physical and functional thermal sensitivity of bacterial chemoreceptors. J Mol Biol 2011; 411:554-66. [PMID: 21718703 DOI: 10.1016/j.jmb.2011.06.006] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/25/2011] [Revised: 05/29/2011] [Accepted: 06/03/2011] [Indexed: 10/18/2022]
Abstract
The bacterium Escherichia coli exhibits chemotactic behavior at temperatures ranging from approximately 20 °C to at least 42 °C. This behavior is controlled by clusters of transmembrane chemoreceptors made from trimers of dimers that are linked together by cross-binding to cytoplasmic components. By detecting fluorescence energy transfer between various components of this system, we studied the underlying molecular behavior of these receptors in vivo and throughout their operating temperature range. We reveal a sharp modulation in the conformation of unclustered and clustered receptor trimers and, consequently, in kinase activity output. These modulations occurred at a characteristic temperature that depended on clustering and were lower for receptors at lower adaptational states. However, in the presence of dynamic adaptation, the response of kinase activity to a stimulus was sustained up to 45 °C, but sensitivity notably decreased. Thus, this molecular system exhibits a clear thermal sensitivity that emerges at the level of receptor trimers, but both receptor clustering and adaptation support the overall robust operation of the system at elevated temperatures.
Collapse
Affiliation(s)
- Vered Frank
- The Racah Institute of Physics, The Hebrew University, Jerusalem 91904, Israel
| | | | | | | |
Collapse
|
33
|
Underbakke ES, Zhu Y, Kiessling LL. Protein footprinting in a complex milieu: identifying the interaction surfaces of the chemotaxis adaptor protein CheW. J Mol Biol 2011; 409:483-95. [PMID: 21463637 PMCID: PMC3179904 DOI: 10.1016/j.jmb.2011.03.040] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/06/2011] [Revised: 03/16/2011] [Accepted: 03/17/2011] [Indexed: 10/18/2022]
Abstract
Characterizing protein-protein interactions in a biologically relevant context is important for understanding the mechanisms of signal transduction. Most signal transduction systems are membrane associated and consist of large multiprotein complexes that undergo rapid reorganization--circumstances that present challenges to traditional structure determination methods. To study protein-protein interactions in a biologically relevant complex milieu, we employed a protein footprinting strategy based on isotope-coded affinity tag (ICAT) reagents. ICAT reagents are valuable tools for proteomics. Here, we show their utility in an alternative application--they are ideal for protein footprinting in complex backgrounds because the affinity tag moiety allows for enrichment of alkylated species prior to analysis. We employed a water-soluble ICAT reagent to monitor cysteine accessibility and thereby to identify residues involved in two different protein-protein interactions in the Escherichia coli chemotaxis signaling system. The chemotaxis system is an archetypal transmembrane signaling pathway in which a complex protein superstructure underlies sophisticated sensory performance. The formation of this superstructure depends on the adaptor protein CheW, which mediates a functionally important bridging interaction between transmembrane receptors and histidine kinase. ICAT footprinting was used to map the surfaces of CheW that interact with the large multidomain histidine kinase CheA, as well as with the transmembrane chemoreceptor Tsr in native E. coli membranes. By leveraging the affinity tag, we successfully identified CheW surfaces responsible for CheA-Tsr interaction. The proximity of the CheA and Tsr binding sites on CheW suggests the formation of a composite CheW-Tsr surface for the recruitment of the signaling kinase to the chemoreceptor complex.
Collapse
Affiliation(s)
- Eric S Underbakke
- Department of Biochemistry, University of Wisconsin-Madison, Madison, WI 53706, USA
| | | | | |
Collapse
|
34
|
Cheong R, Paliwal S, Levchenko A. Models at the single cell level. WILEY INTERDISCIPLINARY REVIEWS-SYSTEMS BIOLOGY AND MEDICINE 2011; 2:34-48. [PMID: 20836009 DOI: 10.1002/wsbm.49] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
Many cellular behaviors cannot be completely captured or appropriately described at the cell population level. Noise induced by stochastic chemical reactions, spatially polarized signaling networks, and heterogeneous cell-cell communication are among the many phenomena that require fine-grained analysis. Accordingly, the mathematical models used to describe such systems must be capable of single cell or subcellular resolution. Here, we review techniques for modeling single cells, including models of stochastic chemical kinetics, spatially heterogeneous intracellular signaling, and spatial stochastic systems. We also briefly discuss applications of each type of model.
Collapse
Affiliation(s)
- Raymond Cheong
- Department of Biomedical Engineering, Johns Hopkins University, Baltimore, MD 21218, USA
| | - Saurabh Paliwal
- Department of Biomedical Engineering, Johns Hopkins University, Baltimore, MD 21218, USA
| | - Andre Levchenko
- Department of Biomedical Engineering, Johns Hopkins University, Baltimore, MD 21218, USA.,Whitaker Institute of Biomedical Engineering and Institute for Cell Engineering, Johns Hopkins University, Baltimore, MD, USA
| |
Collapse
|
35
|
Abstract
There is a long and rich tradition of using ideas from both equilibrium thermodynamics and its microscopic partner theory of equilibrium statistical mechanics. In this chapter, we provide some background on the origins of the seemingly unreasonable effectiveness of ideas from both thermodynamics and statistical mechanics in biology. After making a description of these foundational issues, we turn to a series of case studies primarily focused on binding that are intended to illustrate the broad biological reach of equilibrium thinking in biology. These case studies include ligand-gated ion channels, thermodynamic models of transcription, and recent applications to the problem of bacterial chemotaxis. As part of the description of these case studies, we explore a number of different uses of the famed Monod-Wyman-Changeux (MWC) model as a generic tool for providing a mathematical characterization of two-state systems. These case studies should provide a template for tailoring equilibrium ideas to other problems of biological interest.
Collapse
Affiliation(s)
- Hernan G Garcia
- Department of Physics, California Institute of Technology, Pasadena, California, USA
| | | | | | | | | |
Collapse
|
36
|
Scott KA, Porter SL, Bagg EAL, Hamer R, Hill JL, Wilkinson DA, Armitage JP. Specificity of localization and phosphotransfer in the CheA proteins of Rhodobacter sphaeroides. Mol Microbiol 2010; 76:318-30. [PMID: 20525091 DOI: 10.1111/j.1365-2958.2010.07095.x] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Specificity of protein-protein interactions plays a vital role in signal transduction. The chemosensory pathway of Rhodobacter sphaeroides comprises multiple homologues of chemotaxis proteins characterized in organisms such as Escherichia coli. Three CheA homologues are essential for chemotaxis in R. sphaeroides under laboratory conditions. These CheAs are differentially localized to two chemosensory clusters, one at the cell pole and one in the cytoplasm. The polar CheA, CheA(2), has the same domain structure as E. coli CheA and can phosphorylate all R. sphaeroides chemotaxis response regulators. CheA(3) and CheA(4) independently localize to the cytoplasmic cluster; each protein has a subset of the CheA domains, with CheA(3) phosphorylating CheA(4) together making a functional CheA protein. Interestingly, CheA(3)-P can only phosphorylate two response regulators, CheY(6) and CheB(2). R. sphaeroides CheAs exhibit two interesting differences in specificity: (i) the response regulators that they phosphorylate and (ii) the chemosensory cluster to which they localize. Using a domain-swapping approach we investigated the role of the P1 and P5 CheA domains in determining these specificities. We show that the P1 domain is sufficient to determine which response regulators will be phosphorylated in vitro while the P5 domain is sufficient to localize the CheAs to a specific chemosensory cluster.
Collapse
Affiliation(s)
- Kathryn A Scott
- Oxford Centre for Integrative Systems Biology, University of Oxford, Oxford, UK
| | | | | | | | | | | | | |
Collapse
|
37
|
Abstract
Bacteria are capable of sensing and responding to changes in their environment. One of the ways they do this is via chemotaxis, regulating swimming behaviour. The chemotaxis pathway senses chemoattractant gradients and uses a feedback loop to change the bacterial swimming pattern; this feedback loop differs in detail between species. In the present article, we summarize the current understanding of the regulatory mechanisms in three species and how these pathways can be viewed and analysed through the ideas of feedback control systems engineering.
Collapse
|
38
|
Abstract
Electron cryotomography (ECT) is an emerging technology that allows thin samples such as macromolecular complexes and small bacterial cells to be imaged in 3-D in a nearly native state to "molecular" ( approximately 4 nm) resolution. As such, ECT is beginning to deliver long-awaited insight into the positions and structures of cytoskeletal fi laments, cell wall elements, motility machines, chemoreceptor arrays, internal compartments, and other ultrastructures. This article describes the technique and summarizes its contributions to bacterial cell biology. For comparable recent reviews, see (Subramaniam 2005; Jensen and Briegel 2007; Murphy and Jensen 2007; Li and Jensen 2009). For reviews on the history, technical details, and broader application of electron tomography in general, see for example (Subramaniam and Milne 2004; Lucić et al. 2005; Leis et al. 2008; Midgley and Dunin-Borkowski 2009).
Collapse
Affiliation(s)
- Elitza I Tocheva
- Division of Biology, California Institute of Technology, Pasadena, CA 91125, USA
| | | | | |
Collapse
|
39
|
Bhatnagar J, Borbat PP, Pollard AM, Bilwes AM, Freed JH, Crane BR. Structure of the ternary complex formed by a chemotaxis receptor signaling domain, the CheA histidine kinase, and the coupling protein CheW as determined by pulsed dipolar ESR spectroscopy. Biochemistry 2010; 49:3824-41. [PMID: 20355710 DOI: 10.1021/bi100055m] [Citation(s) in RCA: 66] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
The signaling apparatus that controls bacterial chemotaxis is composed of a core complex containing chemoreceptors, the histidine autokinase CheA, and the coupling protein CheW. Site-specific spin labeling and pulsed dipolar ESR spectroscopy (PDS) have been applied to investigate the structure of a soluble ternary complex formed by Thermotoga maritima CheA (TmCheA), CheW, and receptor signaling domains. Thirty-five symmetric spin-label sites (SLSs) were engineered into the five domains of the CheA dimer and CheW to provide distance restraints within the CheA:CheW complex in the absence and presence of a soluble receptor that inhibits kinase activity (Tm14). Additional PDS restraints among spin-labeled CheA, CheW, and an engineered single-chain receptor labeled at six different sites allow docking of the receptor structure relative to the CheA:CheW complex. Disulfide cross-linking between selectively incorporated Cys residues finds two pairs of positions that provide further constraints within the ternary complex: one involving Tm14 and CheW and another involving Tm14 and CheA. The derived structure of the ternary complex indicates a primary site of interaction between CheW and Tm14 that agrees well with previous biochemical and genetic data for transmembrane chemoreceptors. The PDS distance distributions are most consistent with only one CheW directly engaging one dimeric Tm14. The CheA dimerization domain (P3) aligns roughly antiparallel to the receptor-conserved signaling tip but does not interact strongly with it. The angle of the receptor axis with respect to P3 and the CheW-binding P5 domains is bound by two limits differing by approximately 20 degrees . In one limit, Tm14 aligns roughly along P3 and may interact to some extent with the hinge region near the P3 hairpin loop. In the other limit, Tm14 tilts to interact with the P5 domain of the opposite subunit in an interface that mimics that observed with the P5 homologue CheW. The time domain ESR data can be simulated from the model only if orientational variability is introduced for the P5 and, especially, P3 domains. The Tm14 tip also binds beside one of the CheA kinase domains (P4); however, in both bound and unbound states, P4 samples a broad range of distributions that are only minimally affected by Tm14 binding. The CheA P1 domains that contain the substrate histidine are also broadly distributed in space under all conditions. In the context of the hexagonal lattice formed by trimeric transmembrane chemoreceptors, the PDS structure is best accommodated with the P3 domain in the center of a honeycomb edge.
Collapse
Affiliation(s)
- Jaya Bhatnagar
- Center for Advanced ESR Studies, Cornell University, Ithaca, New York 14853, USA
| | | | | | | | | | | |
Collapse
|
40
|
Miller J, Parker M, Bourret RB, Giddings MC. An agent-based model of signal transduction in bacterial chemotaxis. PLoS One 2010; 5:e9454. [PMID: 20485527 PMCID: PMC2869346 DOI: 10.1371/journal.pone.0009454] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/07/2009] [Accepted: 02/01/2010] [Indexed: 11/17/2022] Open
Abstract
We report the application of agent-based modeling to examine the signal transduction network and receptor arrays for chemotaxis in Escherichia coli, which are responsible for regulating swimming behavior in response to environmental stimuli. Agent-based modeling is a stochastic and bottom-up approach, where individual components of the modeled system are explicitly represented, and bulk properties emerge from their movement and interactions. We present the Chemoscape model: a collection of agents representing both fixed membrane-embedded and mobile cytoplasmic proteins, each governed by a set of rules representing knowledge or hypotheses about their function. When the agents were placed in a simulated cellular space and then allowed to move and interact stochastically, the model exhibited many properties similar to the biological system including adaptation, high signal gain, and wide dynamic range. We found the agent based modeling approach to be both powerful and intuitive for testing hypotheses about biological properties such as self-assembly, the non-linear dynamics that occur through cooperative protein interactions, and non-uniform distributions of proteins in the cell. We applied the model to explore the role of receptor type, geometry and cooperativity in the signal gain and dynamic range of the chemotactic response to environmental stimuli. The model provided substantial qualitative evidence that the dynamic range of chemotactic response can be traced to both the heterogeneity of receptor types present, and the modulation of their cooperativity by their methylation state.
Collapse
Affiliation(s)
- Jameson Miller
- Department of Computer Science, University of North Carolina, Chapel Hill, North Carolina, United States of America
| | | | | | | |
Collapse
|
41
|
Suzuki D, Irieda H, Homma M, Kawagishi I, Sudo Y. Phototactic and chemotactic signal transduction by transmembrane receptors and transducers in microorganisms. SENSORS 2010; 10:4010-39. [PMID: 22319339 PMCID: PMC3274258 DOI: 10.3390/s100404010] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 01/28/2010] [Revised: 03/29/2010] [Accepted: 04/09/2010] [Indexed: 12/17/2022]
Abstract
Microorganisms show attractant and repellent responses to survive in the various environments in which they live. Those phototaxic (to light) and chemotaxic (to chemicals) responses are regulated by membrane-embedded receptors and transducers. This article reviews the following: (1) the signal relay mechanisms by two photoreceptors, Sensory Rhodopsin I (SRI) and Sensory Rhodopsin II (SRII) and their transducers (HtrI and HtrII) responsible for phototaxis in microorganisms; and (2) the signal relay mechanism of a chemoreceptor/transducer protein, Tar, responsible for chemotaxis in E. coli. Based on results mainly obtained by our group together with other findings, the possible molecular mechanisms for phototaxis and chemotaxis are discussed.
Collapse
Affiliation(s)
- Daisuke Suzuki
- Division of Biological Science, Graduate School of Science, Nagoya University, Chikusa-ku, Nagoya, 464-8602, Japan; E-Mails: (D.S.); (H.I.); (M.H.)
| | - Hiroki Irieda
- Division of Biological Science, Graduate School of Science, Nagoya University, Chikusa-ku, Nagoya, 464-8602, Japan; E-Mails: (D.S.); (H.I.); (M.H.)
| | - Michio Homma
- Division of Biological Science, Graduate School of Science, Nagoya University, Chikusa-ku, Nagoya, 464-8602, Japan; E-Mails: (D.S.); (H.I.); (M.H.)
| | - Ikuro Kawagishi
- Department of Frontier Bioscience, Hosei University, Koganei, Tokyo, 184-8584, Japan; E-Mail: (I.K.)
- Research Center for Micro-Nano Technology, Hosei University, Koganei, Tokyo, 184-8584, Japan
| | - Yuki Sudo
- Division of Biological Science, Graduate School of Science, Nagoya University, Chikusa-ku, Nagoya, 464-8602, Japan; E-Mails: (D.S.); (H.I.); (M.H.)
- PRESTO, Japan Science and Technology Agency (JST), 4-1-8 Honcho Kawaguchi, Saitama, 332-0012, Japan
- Author to whom correspondence should be addressed; E-Mail: ; Tel.: +81-52-789-2993; Fax: +81-52-789-3001
| |
Collapse
|
42
|
Fowler DJ, Weis RM, Thompson LK. Kinase-active signaling complexes of bacterial chemoreceptors do not contain proposed receptor-receptor contacts observed in crystal structures. Biochemistry 2010; 49:1425-34. [PMID: 20088541 DOI: 10.1021/bi901565k] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The receptor dimers that mediate bacterial chemotaxis form high-order signaling complexes with CheW and the kinase CheA. From the packing arrangement in two crystal structures of different receptor cytoplasmic fragments, two different models have been proposed for receptor signaling arrays: the trimers-of-dimers and hedgerow models. Here we identified an interdimer distance that differs substantially in the two models, labeled the atoms defining this distance through isotopic enrichment, and measured it with (19)F-(13)C REDOR. This was done in two types of receptor samples: isolated bacterial membranes containing overexpressed, intact receptor and soluble receptor fragments reconstituted into kinase-active signaling complexes. In both cases, the distance found was not compatible with the receptor dimer-dimer contacts observed in the trimers-of-dimers or in the hedgerow models. Comparisons of simulated and observed REDOR dephasing were used to deduce a closest approach distance at this interface, which provides a constraint for the possible arrangements of receptor assemblies.
Collapse
Affiliation(s)
- Daniel J Fowler
- Department of Chemistry, 710 North Pleasant Street, University of Massachusetts, Amherst, Massachusetts 01003, USA
| | | | | |
Collapse
|
43
|
Modelling the molecular mechanisms of synaptic plasticity using systems biology approaches. Nat Rev Neurosci 2010; 11:239-51. [PMID: 20300102 DOI: 10.1038/nrn2807] [Citation(s) in RCA: 145] [Impact Index Per Article: 10.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
Synaptic plasticity is thought to underlie learning and memory, but the complexity of the interactions between the ion channels, enzymes and genes that are involved in synaptic plasticity impedes a deep understanding of this phenomenon. Computer modelling has been used to investigate the information processing that is performed by the signalling pathways involved in synaptic plasticity in principal neurons of the hippocampus, striatum and cerebellum. In the past few years, new software developments that combine computational neuroscience techniques with systems biology techniques have allowed large-scale, kinetic models of the molecular mechanisms underlying long-term potentiation and long-term depression. We highlight important advancements produced by these quantitative modelling efforts and introduce promising approaches that use advancements in live-cell imaging.
Collapse
|
44
|
Abstract
Despite their small size, bacteria have a remarkably intricate internal organization. Bacteria deploy proteins and protein complexes to particular locations and do so in a dynamic manner in lockstep with the organized deployment of their chromosome. The dynamic subcellular localization of protein complexes is an integral feature of regulatory processes of bacterial cells.
Collapse
Affiliation(s)
- L Shapiro
- Department of Developmental Biology, Stanford University, Stanford, CA 94305, USA.
| | | | | |
Collapse
|
45
|
Kriegsmann J, Gregor I, von der Hocht I, Klare J, Engelhard M, Enderlein J, Fitter J. Translational diffusion and interaction of a photoreceptor and its cognate transducer observed in giant unilamellar vesicles by using dual-focus FCS. Chembiochem 2009; 10:1823-9. [PMID: 19551796 DOI: 10.1002/cbic.200900251] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
In order to monitor membrane-protein binding in lipid bilayers at physiological protein concentrations, we employed the recently developed dual-focus fluorescence correlation spectroscopy (2fFCS) technique. In a case study on a photoreceptor consisting of seven transmembrane helices and its cognate transducer (two transmembrane helices), the lateral diffusion for these integral membrane proteins was analyzed in giant unilamellar vesicles (GUVs). The two-dimensional diffusion coefficients of both separately diffusing proteins differ significantly, with D = 2.2 x 10(-8) cm2 s(-1) for the photoreceptor and with D = 4.1 x 10(-8) cm2 s(-1) for the transducer. In GUVs with both membrane proteins present together, we observed significantly smaller diffusion coefficients for labelled transducer molecules; this indicates the presence of larger diffusing units and therefore intermolecular protein binding. Based on the phenomenological dependence of diffusion coefficients on the molecule's cylindrical radius, we are able to estimate the degree of membrane protein binding on a quantitative level.
Collapse
Affiliation(s)
- Jana Kriegsmann
- Research Centre Jülich, ISB 2: Molecular Biophysics, 52425 Jülich, Germany
| | | | | | | | | | | | | |
Collapse
|
46
|
Abstract
Chemoreceptors are key components of the high-performance signal transduction system that controls bacterial chemotaxis. Chemoreceptors are typically localized in a cluster at the cell pole, where interactions among the receptors in the cluster are thought to contribute to the high sensitivity, wide dynamic range, and precise adaptation of the signaling system. Previous structural and genomic studies have produced conflicting models, however, for the arrangement of the chemoreceptors in the clusters. Using whole-cell electron cryo-tomography, here we show that chemoreceptors of different classes and in many different species representing several major bacterial phyla are all arranged into a highly conserved, 12-nm hexagonal array consistent with the proposed "trimer of dimers" organization. The various observed lengths of the receptors confirm current models for the methylation, flexible bundle, signaling, and linker sub-domains in vivo. Our results suggest that the basic mechanism and function of receptor clustering is universal among bacterial species and was thus conserved during evolution.
Collapse
|
47
|
Equilibrium mechanisms of receptor clustering. PROGRESS IN BIOPHYSICS AND MOLECULAR BIOLOGY 2009; 100:18-24. [DOI: 10.1016/j.pbiomolbio.2009.08.003] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
|
48
|
Endres RG. Polar chemoreceptor clustering by coupled trimers of dimers. Biophys J 2009; 96:453-63. [PMID: 19167296 DOI: 10.1016/j.bpj.2008.10.021] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/21/2008] [Accepted: 10/08/2008] [Indexed: 10/21/2022] Open
Abstract
Receptors of bacterial chemotaxis form clusters at the cell poles, where clusters act as "antennas" to amplify small changes in ligand concentration. It is worthy of note that chemoreceptors cluster at multiple length scales. At the smallest scale, receptors form dimers, which assemble into stable timers of dimers. At a large scale, trimers form large polar clusters composed of thousands of receptors. Although much is known about the signaling properties emerging from receptor clusters, it is unknown how receptors localize at the cell poles and what the determining factors are for cluster size. Here, we present a model of polar receptor clustering based on coupled trimers of dimers, where cluster size is determined as a minimum of the cluster-membrane free energy. This energy has contributions from the cluster-membrane elastic energy, penalizing large clusters due to their high intrinsic curvature, and receptor-receptor coupling that favors large clusters. We find that the reduced cluster-membrane curvature mismatch at the curved cell poles leads to large and robust polar clusters, in line with experimental observation, whereas lateral clusters are efficiently suppressed.
Collapse
Affiliation(s)
- Robert G Endres
- Division of Molecular Biosciences and Centre for Integrated Systems Biology at Imperial College, Imperial College London, London, United Kingdom.
| |
Collapse
|
49
|
Role of HAMP domains in chemotaxis signaling by bacterial chemoreceptors. Proc Natl Acad Sci U S A 2008; 105:16555-60. [PMID: 18940922 DOI: 10.1073/pnas.0806401105] [Citation(s) in RCA: 68] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Bacterial chemoreceptors undergo conformational changes in response to variations in the concentration of extracellular ligands. These changes in chemoreceptor structure initiate a series of signaling events that ultimately result in regulation of rotation of the flagellar motor. Here we have used cryo-electron tomography combined with 3D averaging to determine the in situ structure of chemoreceptor assemblies in Escherichia coli cells that have been engineered to overproduce the serine chemoreceptor Tsr. We demonstrate that chemoreceptors are organized as trimers of receptor dimers and display two distinct conformations that differ principally in arrangement of the HAMP domains within each trimer. Ligand binding and methylation alter the distribution of chemoreceptors between the two conformations, with serine binding favoring the "expanded" conformation and chemoreceptor methylation favoring the "compact" conformation. The distinct positions of chemoreceptor HAMP domains within the context of a trimeric unit are thus likely to represent important aspects of chemoreceptor structural changes relevant to chemotaxis signaling. Based on these results, we propose that the compact and expanded conformations represent the "kinase-on" and "kinase-off" states of chemoreceptor trimers, respectively.
Collapse
|
50
|
Different signaling roles of two conserved residues in the cytoplasmic hairpin tip of Tsr, the Escherichia coli serine chemoreceptor. J Bacteriol 2008; 190:8065-74. [PMID: 18931127 DOI: 10.1128/jb.01121-08] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Bacterial chemoreceptors form ternary signaling complexes with the histidine kinase CheA through the coupling protein CheW. Receptor complexes in turn cluster into cellular arrays that produce highly sensitive responses to chemical stimuli. In Escherichia coli, receptors of different types form mixed trimer-of-dimers signaling teams through the tips of their highly conserved cytoplasmic domains. To explore the possibility that the hairpin loop at the tip of the trimer contact region might promote interactions with CheA or CheW, we constructed and characterized mutant receptors with amino acid replacements at the two nearly invariant hairpin charged residues of Tsr: R388, the most tip-proximal trimer contact residue, and E391, the apex residue of the hairpin turn. Mutant receptors were subjected to in vivo tests for the assembly and function of trimers, ternary complexes, and clusters. All R388 replacements impaired or destroyed Tsr function, apparently through changes in trimer stability or geometry. Large-residue replacements locked R388 mutant ternary complexes in the kinase-off (F, H) or kinase-on (W, Y) signaling state, suggesting that R388 contributes to signaling-related conformational changes in the trimer. In contrast, most E391 mutants retained function and all formed ternary signaling complexes efficiently. Hydrophobic replacements of any size (G, A, P, V, I, L, F, W) caused a novel phenotype in which the mutant receptors produced rapid switching between kinase-on and -off states, indicating that hairpin tip flexibility plays an important role in signal state transitions. These findings demonstrate that the receptor determinants for CheA and CheW binding probably lie outside the hairpin tip of the receptor signaling domain.
Collapse
|