1
|
Greve JN, Marquardt A, Heiringhoff R, Reindl T, Thiel C, Di Donato N, Taft MH, Manstein DJ. The non-muscle actinopathy-associated mutation E334Q in cytoskeletal γ-actin perturbs interaction of actin filaments with myosin and ADF/cofilin family proteins. eLife 2024; 12:RP93013. [PMID: 38446501 PMCID: PMC10942649 DOI: 10.7554/elife.93013] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/07/2024] Open
Abstract
Various heterozygous cytoskeletal γ-actin mutations have been shown to cause Baraitser-Winter cerebrofrontofacial syndrome, non-syndromic hearing loss, or isolated eye coloboma. Here, we report the biochemical characterization of human cytoskeletal γ-actin carrying mutation E334Q, a mutation that leads to a hitherto unspecified non-muscle actinopathy. Following expression, purification, and removal of linker and thymosin β4 tag sequences, the p.E334Q monomers show normal integration into linear and branched actin filaments. The mutation does not affect thermal stability, actin filament nucleation, elongation, and turnover. Model building and normal mode analysis predict significant differences in the interaction of p.E334Q filaments with myosin motors and members of the ADF/cofilin family of actin-binding proteins. Assays probing the interactions of p.E334Q filaments with human class 2 and class 5 myosin motor constructs show significant reductions in sliding velocity and actin affinity. E334Q differentially affects cofilin-mediated actin dynamics by increasing the rate of cofilin-mediated de novo nucleation of actin filaments and decreasing the efficiency of cofilin-mediated filament severing. Thus, it is likely that p.E334Q-mediated changes in myosin motor activity, as well as filament turnover, contribute to the observed disease phenotype.
Collapse
Affiliation(s)
- Johannes N Greve
- Institute for Biophysical Chemistry, Hannover Medical School, Fritz Hartmann Centre for MedicalHannoverGermany
| | - Anja Marquardt
- Institute for Biophysical Chemistry, Hannover Medical School, Fritz Hartmann Centre for MedicalHannoverGermany
| | - Robin Heiringhoff
- Institute for Biophysical Chemistry, Hannover Medical School, Fritz Hartmann Centre for MedicalHannoverGermany
| | - Theresia Reindl
- Institute for Biophysical Chemistry, Hannover Medical School, Fritz Hartmann Centre for MedicalHannoverGermany
| | - Claudia Thiel
- Institute for Biophysical Chemistry, Hannover Medical School, Fritz Hartmann Centre for MedicalHannoverGermany
| | | | - Manuel H Taft
- Institute for Biophysical Chemistry, Hannover Medical School, Fritz Hartmann Centre for MedicalHannoverGermany
| | - Dietmar J Manstein
- Institute for Biophysical Chemistry, Hannover Medical School, Fritz Hartmann Centre for MedicalHannoverGermany
- Division for Structural Biochemistry, Hannover Medical SchoolHannoverGermany
- RESiST, Cluster of Excellence 2155, Hannover Medical SchoolHannoverGermany
| |
Collapse
|
2
|
Chen J, Kaw K, Lu H, Fagnant PM, Chattopadhyay A, Duan XY, Zhou Z, Ma S, Liu Z, Huang J, Kamm K, Stull JT, Kwartler CS, Trybus KM, Milewicz DM. Resistance of Acta2 R149C/+ mice to aortic disease is associated with defective release of mutant smooth muscle α-actin from the chaperonin-containing TCP1 folding complex. J Biol Chem 2021; 297:101228. [PMID: 34600884 PMCID: PMC8633019 DOI: 10.1016/j.jbc.2021.101228] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/22/2021] [Revised: 09/12/2021] [Accepted: 09/21/2021] [Indexed: 11/04/2022] Open
Abstract
Pathogenic variants of the gene for smooth muscle α-actin (ACTA2), which encodes smooth muscle (SM) α-actin, predispose to heritable thoracic aortic disease. The ACTA2 variant p.Arg149Cys (R149C) is the most common alteration; however, only 60% of carriers have a dissection or undergo repair of an aneurysm by 70 years of age. A mouse model of ACTA2 p.Arg149Cys was generated using CRISPR/Cas9 technology to determine the etiology of reduced penetrance. Acta2R149C/+ mice had significantly decreased aortic contraction compared with WT mice but did not form aortic aneurysms or dissections when followed to 24 months, even when hypertension was induced. In vitro motility assays found decreased interaction of mutant SM α-actin filaments with SM myosin. Polymerization studies using total internal reflection fluorescence microscopy showed enhanced nucleation of mutant SM α-actin by formin, which correlated with disorganized and reduced SM α-actin filaments in Acta2R149C/+ smooth muscle cells (SMCs). However, the most prominent molecular defect was the increased retention of mutant SM α-actin in the chaperonin-containing t-complex polypeptide folding complex, which was associated with reduced levels of mutant compared with WT SM α-actin in Acta2R149C/+ SMCs. These data indicate that Acta2R149C/+ mice do not develop thoracic aortic disease despite decreased contraction of aortic segments and disrupted SM α-actin filament formation and function in Acta2R149C/+ SMCs. Enhanced binding of mutant SM α-actin to chaperonin-containing t-complex polypeptide decreases the mutant actin versus WT monomer levels in Acta2R149C/+ SMCs, thus minimizing the effect of the mutation on SMC function and potentially preventing aortic disease in the Acta2R149C/+ mice.
Collapse
Affiliation(s)
- Jiyuan Chen
- Division of Medical Genetic, Department of Internal Medicine, McGovern Medical School, University of Texas Health Science Center at Houston, Texas, USA
| | - Kaveeta Kaw
- Division of Medical Genetic, Department of Internal Medicine, McGovern Medical School, University of Texas Health Science Center at Houston, Texas, USA
| | - Hailong Lu
- Department of Molecular Physiology and Biophysics, University of Vermont, Burlington, Vermont, USA
| | - Patricia M Fagnant
- Department of Molecular Physiology and Biophysics, University of Vermont, Burlington, Vermont, USA
| | - Abhijnan Chattopadhyay
- Division of Medical Genetic, Department of Internal Medicine, McGovern Medical School, University of Texas Health Science Center at Houston, Texas, USA
| | - Xue Yan Duan
- Division of Medical Genetic, Department of Internal Medicine, McGovern Medical School, University of Texas Health Science Center at Houston, Texas, USA
| | - Zhen Zhou
- Division of Medical Genetic, Department of Internal Medicine, McGovern Medical School, University of Texas Health Science Center at Houston, Texas, USA
| | - Shuangtao Ma
- Division of Medical Genetic, Department of Internal Medicine, McGovern Medical School, University of Texas Health Science Center at Houston, Texas, USA
| | - Zhenan Liu
- Department of Physiology, University of Texas Southwestern Medical Center, Dallas, Texas, USA
| | - Jian Huang
- Department of Physiology, University of Texas Southwestern Medical Center, Dallas, Texas, USA
| | - Kristine Kamm
- Department of Physiology, University of Texas Southwestern Medical Center, Dallas, Texas, USA
| | - James T Stull
- Department of Physiology, University of Texas Southwestern Medical Center, Dallas, Texas, USA
| | - Callie S Kwartler
- Division of Medical Genetic, Department of Internal Medicine, McGovern Medical School, University of Texas Health Science Center at Houston, Texas, USA
| | - Kathleen M Trybus
- Department of Molecular Physiology and Biophysics, University of Vermont, Burlington, Vermont, USA
| | - Dianna M Milewicz
- Division of Medical Genetic, Department of Internal Medicine, McGovern Medical School, University of Texas Health Science Center at Houston, Texas, USA.
| |
Collapse
|
3
|
Corrêa T, Poswar F, Feltes BC, Riegel M. Candidate Genes Associated With Neurological Findings in a Patient With Trisomy 4p16.3 and Monosomy 5p15.2. Front Genet 2020; 11:561. [PMID: 32625234 PMCID: PMC7311770 DOI: 10.3389/fgene.2020.00561] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/06/2019] [Accepted: 05/11/2020] [Indexed: 12/12/2022] Open
Abstract
In this report, we present a patient with brain alterations and dysmorphic features associated with chromosome duplication seen in 4p16.3 region and chromosomal deletion in a critical region responsible for Cri-du-chat syndrome (CdCS). Chromosomal microarray analysis (CMA) revealed a 41.1 Mb duplication encompassing the band region 4p16.3-p13, and a 14.7 Mb deletion located between the bands 5p15.33 and p15.1. The patient's clinical findings overlap with previously reported cases of chromosome 4p duplication syndrome and CdCS. The patient's symptoms are notably similar to those of CdCS patients as she presented with a weak, high-pitched voice and showed a similar pathogenicity observed in the brain MRI. These contiguous gene syndromes present with distinct clinical manifestations. However, the phenotypic and cytogenetic variability in affected individuals, such as the low frequency and the large genomic regions that can be altered, make it challenging to identify candidate genes that contribute to the pathogenesis of these syndromes. Therefore, systems biology and CMA techniques were used to investigate the extent of chromosome rearrangement on critical regions in our patient's phenotype. We identified the candidate genes PPARGC1A, CTBP1, TRIO, TERT, and CCT5 that are associated with the neuropsychomotor delay, microcephaly, and neurological alterations found in our patient. Through investigating pathways that associate with essential nodes in the protein interaction network, we discovered proteins involved in cellular differentiation and proliferation, as well as proteins involved in the formation and disposition of the cytoskeleton. The combination of our cytogenomic and bioinformatic analysis provided these possible explanations for the unique clinical phenotype, which has not yet been described in scientific literature.
Collapse
Affiliation(s)
- Thiago Corrêa
- Post-Graduate Program in Genetics and Molecular Biology, Genetics Department, Universidade Federal do Rio Grande do Sul, Porto Alegre, Brazil
| | - Fabiano Poswar
- Medical Genetics Service, Hospital de Clínicas de Porto Alegre, Porto Alegre, Brazil
| | - Bruno César Feltes
- Department of Theoritical Informatics, Institute of Informatics, Universidade Federal do Rio Grande do Sul, Porto Alegre, Brazil
| | - Mariluce Riegel
- Post-Graduate Program in Genetics and Molecular Biology, Genetics Department, Universidade Federal do Rio Grande do Sul, Porto Alegre, Brazil
- Medical Genetics Service, Hospital de Clínicas de Porto Alegre, Porto Alegre, Brazil
| |
Collapse
|
4
|
Willison KR. The substrate specificity of eukaryotic cytosolic chaperonin CCT. Philos Trans R Soc Lond B Biol Sci 2019; 373:rstb.2017.0192. [PMID: 29735743 DOI: 10.1098/rstb.2017.0192] [Citation(s) in RCA: 48] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 01/12/2018] [Indexed: 12/22/2022] Open
Abstract
The cytosolic chaperonin CCT (chaperonin containing TCP-1) is an ATP-dependent double-ring protein machine mediating the folding of members of the eukaryotic cytoskeletal protein families. The actins and tubulins are obligate substrates of CCT because they are completely dependent on CCT activity to reach their native states. Genetic and proteomic analysis of the CCT interactome in the yeast Saccharomyces cerevisiae revealed a CCT network of approximately 300 genes and proteins involved in many fundamental biological processes. We classified network members into sets such as substrates, CCT cofactors and CCT-mediated assembly processes. Many members of the 7-bladed propeller family of proteins are commonly found tightly bound to CCT isolated from human and plant cells and yeasts. The anaphase promoting complex (APC/C) cofactor propellers, Cdh1p and Cdc20p, are also obligate substrates since they both require CCT for folding and functional activation. In vitro translation analysis in prokaryotic and eukaryotic cell extracts of a set of yeast propellers demonstrates their highly differential interactions with CCT and GroEL (another chaperonin). Individual propeller proteins have idiosyncratic interaction modes with CCT because they emerged independently with neo-functions many times throughout eukaryotic evolution. We present a toy model in which cytoskeletal protein biogenesis and folding flux through CCT couples cell growth and size control to time dependent cell cycle mechanisms.This article is part of a discussion meeting issue 'Allostery and molecular machines'.
Collapse
Affiliation(s)
- Keith R Willison
- Department of Chemistry, Imperial College London, South Kensington Campus, London SW7 2AZ, UK
| |
Collapse
|
5
|
The structure and evolution of eukaryotic chaperonin-containing TCP-1 and its mechanism that folds actin into a protein spring. Biochem J 2018; 475:3009-3034. [DOI: 10.1042/bcj20170378] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/03/2018] [Revised: 08/16/2018] [Accepted: 08/28/2018] [Indexed: 12/15/2022]
Abstract
Actin is folded to its native state in eukaryotic cytosol by the sequential allosteric mechanism of the chaperonin-containing TCP-1 (CCT). The CCT machine is a double-ring ATPase built from eight related subunits, CCT1–CCT8. Non-native actin interacts with specific subunits and is annealed slowly through sequential binding and hydrolysis of ATP around and across the ring system. CCT releases a folded but soft ATP-G-actin monomer which is trapped 80 kJ/mol uphill on the folding energy surface by its ATP-Mg2+/Ca2+ clasp. The energy landscape can be re-explored in the actin filament, F-actin, because ATP hydrolysis produces dehydrated and more compact ADP-actin monomers which, upon application of force and strain, are opened and closed like the elements of a spring. Actin-based myosin motor systems underpin a multitude of force generation processes in cells and muscles. We propose that the water surface of F-actin acts as a low-binding energy, directional waveguide which is recognized specifically by the myosin lever-arm domain before the system engages to form the tight-binding actomyosin complex. Such a water-mediated recognition process between actin and myosin would enable symmetry breaking through fast, low energy initial binding events. The origin of chaperonins and the subsequent emergence of the CCT–actin system in LECA (last eukaryotic common ancestor) point to the critical role of CCT in facilitating phagocytosis during early eukaryotic evolution and the transition from the bacterial world. The coupling of CCT-folding fluxes to the cell cycle, cell size control networks and cancer are discussed together with directions for further research.
Collapse
|
6
|
Sehrawat U, Pokhriyal R, Gupta AK, Hariprasad R, Khan MI, Gupta D, Naru J, Singh SB, Mohanty AK, Vanamail P, Kumar L, Kumar S, Hariprasad G. Comparative Proteomic Analysis of Advanced Ovarian Cancer Tissue to Identify Potential Biomarkers of Responders and Nonresponders to First-Line Chemotherapy of Carboplatin and Paclitaxel. BIOMARKERS IN CANCER 2016; 8:43-56. [PMID: 26997873 PMCID: PMC4795487 DOI: 10.4137/bic.s35775] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 10/21/2015] [Revised: 02/08/2016] [Accepted: 02/11/2016] [Indexed: 12/16/2022]
Abstract
Conventional treatment for advanced ovarian cancer is an initial debulking surgery followed by chemotherapy combination of carboplatin and paclitaxel. Despite initial high response, three-fourths of these women experience disease recurrence with a dismal prognosis. Patients with advanced-stage ovarian cancer who underwent cytoreductive surgery were enrolled and tissue samples were collected. Post surgery, these patients were started on chemotherapy and followed up till the end of the cycle. Fluorescence-based differential in-gel expression coupled with mass spectrometric analysis was used for discovery phase of experiments, and real-time polymerase chain reaction, Western blotting, and pathway analysis were performed for expression and functional validation of differentially expressed proteins. While aldehyde reductase, hnRNP, cyclophilin A, heat shock protein-27, and actin are upregulated in responders, prohibitin, enoyl-coA hydratase, peroxiredoxin, and fibrin-β are upregulated in the nonresponders. The expressions of some of these proteins correlated with increased apoptotic activity in responders and decreased apoptotic activity in nonresponders. Therefore, the proteins qualify as potential biomarkers to predict chemotherapy response.
Collapse
Affiliation(s)
- Urmila Sehrawat
- Department of Biophysics, All India Institute of Medical Sciences, Ansari Nagar, New Delhi, India
| | - Ruchika Pokhriyal
- Department of Biophysics, All India Institute of Medical Sciences, Ansari Nagar, New Delhi, India
| | - Ashish Kumar Gupta
- Department of Biophysics, All India Institute of Medical Sciences, Ansari Nagar, New Delhi, India
| | - Roopa Hariprasad
- Department of Medical Oncology, All India Institute of Medical Sciences, Ansari Nagar, New Delhi, India
| | - Mohd Imran Khan
- Department of Biophysics, All India Institute of Medical Sciences, Ansari Nagar, New Delhi, India
| | - Divya Gupta
- Department of Biophysics, All India Institute of Medical Sciences, Ansari Nagar, New Delhi, India
| | - Jasmine Naru
- National Dairy Research Institute, Karnal, India
| | | | | | - Perumal Vanamail
- Department of Obstetrics and Gynecology, All India Institute of Medical Sciences, Ansari Nagar, New Delhi, India
| | - Lalit Kumar
- Department of Medical Oncology, All India Institute of Medical Sciences, Ansari Nagar, New Delhi, India
| | - Sunesh Kumar
- Department of Obstetrics and Gynecology, All India Institute of Medical Sciences, Ansari Nagar, New Delhi, India
| | - Gururao Hariprasad
- Department of Biophysics, All India Institute of Medical Sciences, Ansari Nagar, New Delhi, India
| |
Collapse
|
7
|
Lehtonen HJ, Sipponen T, Tojkander S, Karikoski R, Järvinen H, Laing NG, Lappalainen P, Aaltonen LA, Tuupanen S. Segregation of a missense variant in enteric smooth muscle actin γ-2 with autosomal dominant familial visceral myopathy. Gastroenterology 2012; 143:1482-1491.e3. [PMID: 22960657 DOI: 10.1053/j.gastro.2012.08.045] [Citation(s) in RCA: 69] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/18/2012] [Revised: 08/13/2012] [Accepted: 08/28/2012] [Indexed: 12/20/2022]
Abstract
BACKGROUND & AIMS Familial visceral myopathy (FVM) is a rare inherited form of myopathic pseudo-obstruction; little is known about the genetic factors that cause this disorder. FVM is characterized by impaired functions of enteric smooth muscle cells, resulting in abnormal intestinal motility, severe abdominal pain, malnutrition, and even death. We searched for genetic factors that might cause this disorder. METHODS We performed whole-exome sequence analysis of blood samples from 2 individuals in a family that had 7 members diagnosed with FVM. Sanger sequencing was used to analyze additional family members and 280 individuals without this disorder (controls). Intestinal tissue samples from 4 patients and 2 controls were analyzed by immunohistochemistry. Functional studies, including immunofluorescence, cell contractility, and actomyosin structure analyses, were performed using CRL-1976 and U2OS sarcoma cell lines. RESULTS Whole-exome sequence analysis of DNA from 2 siblings identified 83 gene variants that were shared between the siblings and considered as possible disease-causing changes. A heterozygous variant, R148S in enteric smooth muscle actin γ-2 (ACTG2), segregated with disease phenotype. Intestinal smooth muscle (muscularis propria) from individuals with FVM had reduced levels of cytoplasmic ACTG2 and abnormal accumulation of the protein into intracellular inclusions compared with controls. Sarcoma cells that expressed exogenous ACTG2(R148S) incorporated reduced amounts of this protein into actin filaments compared with cells expressing ACTG2(wt) (P < .001). ACTG2(R148S) also interfered with actin cytoskeleton organization and the contractile activities of the cells, indicating a dominant-negative effect. These findings, along with the site of the variation in the protein, indicate that ACTG2 R148S interferes with actin filament assembly. CONCLUSIONS We identified the R148S variant in ACTG2 as a cause of FVM in one family. The altered ACTG2 protein appears to aggregate, rather than form actin filaments, in intestinal smooth muscle tissue. This defect could impair contraction of the visceral smooth muscle cells and reduce bowel motility.
Collapse
Affiliation(s)
- Heli J Lehtonen
- Department of Medical Genetics, Genome-Scale Biology Research Program, Biomedicum Helsinki, University of Helsinki, Helsinki, Finland
| | | | | | | | | | | | | | | | | |
Collapse
|
8
|
Folding of large multidomain proteins by partial encapsulation in the chaperonin TRiC/CCT. Proc Natl Acad Sci U S A 2012. [PMID: 23197838 DOI: 10.1073/pnas.1218836109] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023] Open
Abstract
The eukaryotic chaperonin, TRiC/CCT (TRiC, TCP-1 ring complex; CCT, chaperonin containing TCP-1), uses a built-in lid to mediate protein folding in an enclosed central cavity. Recent structural data suggest an effective size limit for the TRiC folding chamber of ∼70 kDa, but numerous chaperonin substrates are substantially larger. Using artificial fusion constructs with actin, an obligate chaperonin substrate, we show that TRiC can mediate folding of large proteins by segmental or domain-wise encapsulation. Single or multiple protein domains up to ∼70 kDa are stably enclosed by stabilizing the ATP-hydrolysis transition state of TRiC. Additional domains, connected by flexible linkers that pass through the central opening of the folding chamber, are excluded and remain accessible to externally added protease. Experiments with the physiological TRiC substrate hSnu114, a 109-kDa multidomain protein, suggest that TRiC has the ability to recognize domain boundaries in partially folded intermediates. In the case of hSnu114, this allows the selective encapsulation of the C-terminal ∼45-kDa domain and segments thereof, presumably reflecting a stepwise folding mechanism. The capacity of the eukaryotic chaperonin to overcome the size limitation of the folding chamber may have facilitated the explosive expansion of the multidomain proteome in eukaryotes.
Collapse
|
9
|
Lee JY, Duan L, Iverson TM, Dima RI. Exploring the role of topological frustration in actin refolding with molecular simulations. J Phys Chem B 2012; 116:1677-86. [PMID: 22243338 DOI: 10.1021/jp209340y] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Actin plays crucial roles in the life of the cell while being notorious for its inability to reach a functional conformation without the help of assistant proteins. In eukaryotes, for example, the cytosolic chaperonin containing TCP-1 (CCT) and prefoldin (PFD) are required for actin folding assistance and prevention of protein aggregation in the crowded cellular environment. The folding of non-native actin is known to occur in a number of steps, but the reasons underlying its folding difficulty are unknown. Because a full, atomistic-level, investigation of the kinetics and thermodynamics of folding of such a large molecule is beyond computational reach, we focused our investigation on the role of topological frustration on the folding of actin. Namely, we studied the (re)folding of actin using simulations of a variant self-organized polymer model (SOP-DH) starting from a stretched state, leading to results that correlate well with experimentally driven conclusions and allowing us to make a number of testable predictions. Primarily, our simulations reveal that the successful refolding of the C-terminus end of actin occurs through a zipping process in which the α-helices wind up turn by turn upon formation of their native tertiary contacts. In turn, an early formation of the helical structure in this region of the chain has deleterious effects for actin's refolding fitness. Moreover, the C-terminus refolding is a very rare event in our simulations, in agreement with the large activation barrier predicted on the basis of experimental studies of actin unfolding in EDTA. We also discovered that subdomain 4 has a low refolding probability, which can help explain why many of the non-native actin target binding sites for CCT and PFD are located within this subdomain.
Collapse
Affiliation(s)
- Ji Young Lee
- Department of Chemistry, University of Cincinnati, Cincinnati, Ohio 45221, USA
| | | | | | | |
Collapse
|
10
|
Hildenbrand ZL, Bernal RA. Chaperonin-Mediated Folding of Viral Proteins. VIRAL MOLECULAR MACHINES 2012; 726:307-24. [DOI: 10.1007/978-1-4614-0980-9_13] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/16/2023]
|
11
|
Kabir MA, Uddin W, Narayanan A, Reddy PK, Jairajpuri MA, Sherman F, Ahmad Z. Functional Subunits of Eukaryotic Chaperonin CCT/TRiC in Protein Folding. JOURNAL OF AMINO ACIDS 2011; 2011:843206. [PMID: 22312474 PMCID: PMC3268035 DOI: 10.4061/2011/843206] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 02/15/2011] [Accepted: 04/05/2011] [Indexed: 12/22/2022]
Abstract
Molecular chaperones are a class of proteins responsible for proper folding of a large number of polypeptides in both prokaryotic and eukaryotic cells. Newly synthesized polypeptides are prone to nonspecific interactions, and many of them make toxic aggregates in absence of chaperones. The eukaryotic chaperonin CCT is a large, multisubunit, cylindrical structure having two identical rings stacked back to back. Each ring is composed of eight different but similar subunits and each subunit has three distinct domains. CCT assists folding of actin, tubulin, and numerous other cellular proteins in an ATP-dependent manner. The catalytic cooperativity of ATP binding/hydrolysis in CCT occurs in a sequential manner different from concerted cooperativity as shown for GroEL. Unlike GroEL, CCT does not have GroES-like cofactor, rather it has a built-in lid structure responsible for closing the central cavity. The CCT complex recognizes its substrates through diverse mechanisms involving hydrophobic or electrostatic interactions. Upstream factors like Hsp70 and Hsp90 also work in a concerted manner to transfer the substrate to CCT. Moreover, prefoldin, phosducin-like proteins, and Bag3 protein interact with CCT and modulate its function for the fine-tuning of protein folding process. Any misregulation of protein folding process leads to the formation of misfolded proteins or toxic aggregates which are linked to multiple pathological disorders.
Collapse
Affiliation(s)
- M Anaul Kabir
- Molecular Genetics Laboratory, School of Biotechnology, National Institute of Technology Calicut, Kerala 673601, India
| | | | | | | | | | | | | |
Collapse
|
12
|
The crystal structure of yeast CCT reveals intrinsic asymmetry of eukaryotic cytosolic chaperonins. EMBO J 2011; 30:3078-90. [PMID: 21701561 DOI: 10.1038/emboj.2011.208] [Citation(s) in RCA: 86] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/17/2010] [Accepted: 05/11/2011] [Indexed: 01/17/2023] Open
Abstract
The cytosolic chaperonin CCT is a 1-MDa protein-folding machine essential for eukaryotic life. The CCT interactome shows involvement in folding and assembly of a small range of proteins linked to essential cellular processes such as cytoskeleton assembly and cell-cycle regulation. CCT has a classic chaperonin architecture, with two heterogeneous 8-membered rings stacked back-to-back, enclosing a folding cavity. However, the mechanism by which CCT assists folding is distinct from other chaperonins, with no hydrophobic wall lining a potential Anfinsen cage, and a sequential rather than concerted ATP hydrolysis mechanism. We have solved the crystal structure of yeast CCT in complex with actin at 3.8 Å resolution, revealing the subunit organisation and the location of discrete patches of co-evolving 'signature residues' that mediate specific interactions between CCT and its substrates. The intrinsic asymmetry is revealed by the structural individuality of the CCT subunits, which display unique configurations, substrate binding properties, ATP-binding heterogeneity and subunit-subunit interactions. The location of the evolutionarily conserved N-terminus of Cct5 on the outside of the barrel, confirmed by mutational studies, is unique to eukaryotic cytosolic chaperonins.
Collapse
|
13
|
Stuart SF, Leatherbarrow RJ, Willison KR. A two-step mechanism for the folding of actin by the yeast cytosolic chaperonin. J Biol Chem 2010; 286:178-84. [PMID: 21056978 DOI: 10.1074/jbc.m110.166256] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Actin requires the chaperonin containing TCP1 (CCT), a hexadecameric ATPase essential for cell viability in eukaryotes, to fold to its native state. Following binding of unfolded actin to CCT, the cavity of the chaperone closes and actin is folded and released in an ATP-dependent folding cycle. In yeast, CCT forms a ternary complex with the phosducin-like protein PLP2p to fold actin, and together they can return nascent or chemically denatured actin to its native state in a pure in vitro folding assay. The complexity of the CCT-actin system makes the study of the actin folding mechanism technically challenging. We have established a novel spectroscopic assay through selectively labeling the C terminus of yeast actin with acrylodan and observe significant changes in the acrylodan fluorescence emission spectrum as actin is chemically unfolded and then refolded by the chaperonin. The variation in the polarity of the environment surrounding the fluorescent probe during the unfolding/folding processes has allowed us to monitor actin as it folds on CCT. The rate of actin folding at a range of temperatures and ATP concentrations has been determined for both wild type CCT and a mutant CCT, CCT4anc2, defective in folding actin in vivo. Binding of the non-hydrolysable ATP analog adenosine 5'-(β,γ-imino)triphosphate to the ternary complex leads to 3-fold faster release of actin from CCT following addition of ATP, suggesting a two-step folding process with a conformational change occurring upon closure of the cavity and a subsequent final folding step involving packing of the C terminus to the native-like state.
Collapse
Affiliation(s)
- Sarah F Stuart
- Institute of Chemical Biology, Imperial College London, London SW7 2AZ, United Kingdom
| | | | | |
Collapse
|
14
|
Galkin VE, Orlova A, Schröder GF, Egelman EH. Structural polymorphism in F-actin. Nat Struct Mol Biol 2010; 17:1318-23. [PMID: 20935633 PMCID: PMC2988880 DOI: 10.1038/nsmb.1930] [Citation(s) in RCA: 149] [Impact Index Per Article: 9.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/10/2010] [Accepted: 09/15/2010] [Indexed: 12/31/2022]
Abstract
Actin has maintained an exquisite degree of sequence conservation over large evolutionary distances for reasons that are not understood. The desire to explain phenomena from muscle contraction to cytokinesis in mechanistic detail has driven the generation of an atomic model of the actin filament (F-actin). Here we use electron cryomicroscopy to show that frozen-hydrated actin filaments contain a multiplicity of different structural states. We show (at ∼10 Å resolution) that subdomain 2 can be disordered and can make multiple contacts with the C terminus of a subunit above it. We link a number of disease-causing mutations in the human ACTA1 gene to the most structurally dynamic elements of actin. Because F-actin is structurally polymorphic, it cannot be described using only one atomic model and must be understood as an ensemble of different states.
Collapse
Affiliation(s)
- Vitold E Galkin
- Department of Biochemistry and Molecular Genetics, University of Virginia, Charlottesville, Virginia, USA.
| | | | | | | |
Collapse
|
15
|
McCormack EA, Altschuler GM, Dekker C, Filmore H, Willison KR. Yeast phosducin-like protein 2 acts as a stimulatory co-factor for the folding of actin by the chaperonin CCT via a ternary complex. J Mol Biol 2009; 391:192-206. [PMID: 19501098 DOI: 10.1016/j.jmb.2009.06.003] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2009] [Revised: 05/28/2009] [Accepted: 06/01/2009] [Indexed: 11/18/2022]
Abstract
The eukaryotic chaperonin-containing TCP-1 (CCT) folds the cytoskeletal protein actin. The folding mechanism of this 16-subunit, 1-MDa machine is poorly characterised due to the absence of quantitative in vitro assays. We identified phosducin-like protein 2, Plp2p (=PLP2), as an ATP-elutable binding partner of yeast CCT while establishing the CCT interactome. In a novel in vitro CCT-ACT1 folding assay that is functional under physiological conditions, PLP2 is a stimulatory co-factor. In a single ATP-driven cycle, PLP2-CCT-ACT1 complexes yield 30-fold more native actin than CCT-ACT1 complexes. PLP2 interacts directly with ACT1 through the C-terminus of its thioredoxin fold and the CCT-binding subdomain 4 of actin. The in vitro CCT-ACT1-PLP2 folding cycle of the preassembled complex takes 90 s at 30 degrees C, several times slower than the canonical chaperonin GroEL. The specific interactions between PLP2, CCT and ACT1 in the yeast-component in vitro system and the pronounced stimulatory effect of PLP2 on actin folding are consistent with in vivo genetic approaches demonstrating an essential and positive role for PLP2 in cellular processes involving actin in Saccharomyces cerevisiae. In mammalian systems, however, several members of the PLP family, including human PDCL3, the orthologue of PLP2, have been shown to be inhibitory toward CCT-mediated folding of actin in vivo and in vitro. Here, using a rabbit-reticulocyte-derived in vitro translation system, we found that inhibition of beta-actin folding by PDCL3 can be relieved by exchanging its acidic C-terminal extension for that of PLP2. It seems that additional levels of regulatory control of CCT activity by this PLP have emerged in higher eukaryotes.
Collapse
Affiliation(s)
- Elizabeth A McCormack
- Protein Folding and Assembly Team, Section of Cell and Molecular Biology, Chester Beatty Laboratories, Institute of Cancer Research, 237 Fulham Road, London, UK
| | | | | | | | | |
Collapse
|
16
|
Vandamme D, Lambert E, Waterschoot D, Cognard C, Vandekerckhove J, Ampe C, Constantin B, Rommelaere H. alpha-Skeletal muscle actin nemaline myopathy mutants cause cell death in cultured muscle cells. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2009; 1793:1259-71. [PMID: 19393268 DOI: 10.1016/j.bbamcr.2009.04.004] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/23/2008] [Revised: 03/24/2009] [Accepted: 04/14/2009] [Indexed: 11/24/2022]
Abstract
Nemaline myopathy is a neuromuscular disorder, characterized by muscle weakness and hypotonia and is, in 20% of the cases, caused by mutations in the gene encoding alpha-skeletal muscle actin, ACTA1. It is a heterogeneous disease with various clinical phenotypes and severities. In patients the ultrastructure of muscle cells is often disturbed by nemaline rods and it is thought this is the cause for muscle weakness. To search for possible defects during muscle cell differentiation we expressed alpha-actin mutants in myoblasts and allowed these cells to differentiate into myotubes. Surprisingly, we observed two striking new phenotypes in differentiating myoblasts: rounding up of cells and bleb formation, two features reminiscent of apoptosis. Indeed expression of these mutants induced cell death with apoptotic features in muscle cell culture, using AIF and endonuclease G, in a caspase-independent but calpain-dependent pathway. This is the first report on a common cellular defect induced by NM causing actin mutants, independent of their biochemical phenotypes or rod and aggregate formation capacity. These data suggest that lack of type II fibers or atrophy observed in nemaline myopathy patients may be also due to an increased number of dying muscle cells.
Collapse
Affiliation(s)
- Drieke Vandamme
- Department of Biochemistry, Ghent University, A. Baertsoenkaai 3, B-9000, Gent, Belgium
| | | | | | | | | | | | | | | |
Collapse
|
17
|
Altschuler GM, Willison KR. Development of free-energy-based models for chaperonin containing TCP-1 mediated folding of actin. J R Soc Interface 2009; 5:1391-408. [PMID: 18708324 DOI: 10.1098/rsif.2008.0185] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023] Open
Abstract
A free-energy-based approach is used to describe the mechanism through which chaperonin-containing TCP-1 (CCT) folds the filament-forming cytoskeletal protein actin, which is one of its primary substrates. The experimental observations on the actin folding and unfolding pathways are collated and then re-examined from this perspective, allowing us to determine the position of the CCT intervention on the actin free-energy folding landscape. The essential role for CCT in actin folding is to provide a free-energy contribution from its ATP cycle, which drives actin to fold from a stable, trapped intermediate I3, to a less stable but now productive folding intermediate I2. We develop two hypothetical mechanisms for actin folding founded upon concepts established for the bacterial type I chaperonin GroEL and extend them to the much more complex CCT system of eukaryotes. A new model is presented in which CCT facilitates free-energy transfer through direct coupling of the nucleotide hydrolysis cycle to the phases of actin substrate maturation.
Collapse
Affiliation(s)
- Gabriel M Altschuler
- Cancer Research UK Centre for Cell and Molecular Biology, Chester Beatty Laboratories, Institute of Cancer Research, 237 Fulham Road, London SW3 6JB, UK
| | | |
Collapse
|
18
|
Reisler E, Egelman EH. Actin Structure and Function: What We Still Do Not Understand. J Biol Chem 2007; 282:36133-7. [DOI: 10.1074/jbc.r700030200] [Citation(s) in RCA: 76] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
|
19
|
Ruano-Rubio V, Fares MA. Testing the Neutral Fixation of Hetero-Oligomerism in the Archaeal Chaperonin CCT. Mol Biol Evol 2007; 24:1384-96. [PMID: 17406022 DOI: 10.1093/molbev/msm065] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
The evolutionary transition from homo-oligomerism to hetero-oligomerism in multimeric proteins and its contribution to function innovation and organism complexity remain to be investigated. Here, we undertake the challenge of contributing to this theoretical ground by investigating the hetero-oligomerism in the molecular chaperonin cytosolic chaperonin containing tailless complex polypeptide 1 (CCT) from archaea. CCT is amenable to this study because, in contrast to eukaryotic CCTs where sub-functionalization after gene duplication has been taken to completion, archaeal CCTs present no evidence for subunit functional specialization. Our analyses yield additional information to previous reports on archaeal CCT paralogy by identifying new duplication events. Analyses of selective constraints show that amino acid sites from 1 subunit have fixed slightly deleterious mutations at inter-subunit interfaces after gene duplication. These mutations have been followed by compensatory mutations in nearby regions of the same subunit and in the interface contact regions of its paralogous subunit. The strong selective constraints in these regions after speciation support the evolutionary entrapment of CCTs as hetero-oligomers. In addition, our results unveil different evolutionary dynamics depending on the degree of CCT hetero-oligomerism. Archaeal CCT protein complexes comprising 3 distinct classes of subunits present 2 evolutionary processes. First, slightly deleterious and compensatory mutations were fixed neutrally at inter-subunit regions. Second, sub-functionalization may have occurred at substrate-binding and adenosine triphosphate-binding regions after the 2nd gene duplication event took place. CCTs with 2 distinct types of subunits did not present evidence of sub-functionalization. Our results provide the 1st in silico evidence for the neutral fixation of hetero-oligomerism in archaeal CCTs and provide information on the evolution of hetero-oligomerism toward sub-functionalization in archaeal CCTs.
Collapse
Affiliation(s)
- Valentin Ruano-Rubio
- Evolutionary Genetics and Bioinformatics Laboratory, Department of Genetics, Smurfit Institute of Genetics, University of Dublin, Trinity College, Dublin, Ireland
| | | |
Collapse
|
20
|
Grantham J, Brackley KI, Willison KR. Substantial CCT activity is required for cell cycle progression and cytoskeletal organization in mammalian cells. Exp Cell Res 2006; 312:2309-24. [PMID: 16765944 DOI: 10.1016/j.yexcr.2006.03.028] [Citation(s) in RCA: 102] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/24/2005] [Revised: 03/15/2006] [Accepted: 03/22/2006] [Indexed: 10/24/2022]
Abstract
The chaperonin CCT hexadecamer is required for the folding of non-native actins and tubulins in eukaryotic cells. Among the consequences of greatly reducing CCT holocomplex levels in human cell lines by siRNA targeting are growth arrest and changes in cell morphology and motility. Less extensive reduction of CCT activity via microinjection of an inhibitory anti-CCT epsilon subunit monoclonal antibody, which alters the rates of substrate processing by CCT in vitro, causes a delay in cell cycle progression through G1/S phase in synchronized Swiss 3T3 cells. The degree of growth arrest strongly correlates with the extent of CCT depletion, indicating that full CCT activity is required for normal cell growth and division. Depletion of CCT does not affect actin polypeptide synthesis but causes a reduction in levels of native actin and perturbation of actin-based cell motility in BE cells. There are no large-scale effects on cytoplasmic protein synthesis or a general heat shock response during periods of low CCT activity.
Collapse
Affiliation(s)
- Julie Grantham
- Cancer Research UK Centre for Cell and Molecular Biology, Chester Beatty Laboratories, The Institute of Cancer Research, 237 Fulham Road, London SW3 6JB, UK.
| | | | | |
Collapse
|
21
|
Pappenberger G, McCormack EA, Willison KR. Quantitative actin folding reactions using yeast CCT purified via an internal tag in the CCT3/gamma subunit. J Mol Biol 2006; 360:484-96. [PMID: 16762366 DOI: 10.1016/j.jmb.2006.05.003] [Citation(s) in RCA: 59] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/09/2006] [Revised: 04/28/2006] [Accepted: 05/01/2006] [Indexed: 11/16/2022]
Abstract
The eukaryotic cytosolic chaperonin CCT is an essential ATP-dependent protein folding machine whose action is required for folding the cytoskeletal proteins actin and tubulin, and a small number of other substrates, including members of the WD40-propellor repeat-containing protein family. An efficient purification protocol for CCT from Saccharomyces cerevisiae has been developed. It uses the calmodulin binding peptide as an affinity tag in an internal loop in the apical domain of the CCT3 subunit, which is predicted to be located on the outside of the double-ring assembly. This purified yeast CCT was used for a novel quantitative actin-folding assay with human beta-actin or yeast ACT1p protein folding intermediates, Ac(I), pre-synthesised in an Escherichia coli translation system. The formation of native actin follows approximately a first-order reaction with a rate constant of about 0.03 min(-1). Yeast CCT catalyses the folding of yeast ACT1p and human beta-actin with nearly identical rate constants and yields. The results from this controlled CCT-actin folding assay are consistent with a model where CCT and Ac(I) are in a binding pre-equilibrium with a rate-limiting binding step, followed by a faster ATP-driven processing to native actin. In this pure in vitro system, the human beta-actin mutants, D244S and G150P, show impaired folding behaviour in the manner predicted by our sequence-specific recognition model for CCT-actin interaction.
Collapse
Affiliation(s)
- Günter Pappenberger
- Cancer Research U.K., Centre for Cell and Molecular Biology, Chester Beatty Laboratories, Institute of Cancer Research, 237 Fulham Road, London SW3 6JB, UK
| | | | | |
Collapse
|
22
|
Neirynck K, Waterschoot D, Vandekerckhove J, Ampe C, Rommelaere H. Actin Interacts with CCT via Discrete Binding Sites: A Binding transition-release Model for CCT-Mediated Actin Folding. J Mol Biol 2006; 355:124-38. [PMID: 16300788 DOI: 10.1016/j.jmb.2005.10.051] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2005] [Revised: 09/29/2005] [Accepted: 10/18/2005] [Indexed: 11/28/2022]
Abstract
The chaperones prefoldin and the cytosolic chaperonin CCT-containing TCP-1 (CCT) guide the cytoskeletal protein actin to its native conformation. Performing an alanine scan of actin, we identified discrete recognition determinants for CCT interaction. Interestingly, one of these is similar and functional in the non-homologous protein Cdc20, suggesting that some of the binding information in the CCT target proteins is shared. The information in actin for recognition by CCT and for folding is different, as all but one of the mutants in the recognition determinants are folding-competent. In addition, some other actin mutants remain CCT-arrested and are not released in a native conformation, whereas others do fold but remain bound to CAP. Kinetic experiments provide evidence that CCT-mediated folding of non-native actin occurs in at least two steps, in which initially the recognition determinant 245-249 contacts CCT and the other determinants interact at later stages. Actin mutants that are CCT-arrested demonstrate that some regions neighbouring the recognition determinants are involved in modulating the correct folding transitions of actin on CCT, or its release from this chaperonin. Further, we found that the ATP binding of actin is not a prerequisite for its release, and we suggest that CAP may be involved in charging the nucleotide. Based on the kinetics of CCT binding and folding of actin and actin mutants, we propose a multi-step recognition-transition-release model. This also implies that the currently accepted notion of CCT-mediated actin folding is probably more complex.
Collapse
Affiliation(s)
- Katrien Neirynck
- Flanders Interuniversity Institute for Biotechnology (VIB 09) and Department of Biochemistry, Faculty of Medicine and Health Sciences, Ghent University. A. Baertsoenkaai 3, 9000 Gent, Belgium
| | | | | | | | | |
Collapse
|
23
|
Cheng B, Feng J, Gadgil S, Tse-Dinh YC. Flexibility at Gly-194 is required for DNA cleavage and relaxation activity of Escherichia coli DNA topoisomerase I. J Biol Chem 2004; 279:8648-54. [PMID: 14711811 DOI: 10.1074/jbc.m312095200] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The proposed mechanism of type IA DNA topoisomerase I includes conformational changes by the single enzyme polypeptide to allow binding of the G strand of the DNA substrate at the active site, and the opening or closing of the "gate" created on the G strand of DNA to the passing single or double DNA strand(s) through the cleaved G strand DNA. The shifting of an alpha helix upon G strand DNA binding has been observed from the comparison of the type IA DNA topoisomerase crystal structures. Site-directed mutagenesis of the strictly conserved Gly-194 at the N terminus of this alpha helix in Escherichia coli DNA topoisomerase I showed that flexibility around this glycine residue is required for DNA cleavage and relaxation activity and supports a functional role for this hinge region in the enzyme conformational change.
Collapse
Affiliation(s)
- Bokun Cheng
- Department of Biochemistry and Molecular Biology, New York Medical College, Valhalla, New York 10595, USA
| | | | | | | |
Collapse
|
24
|
Posern G, Sotiropoulos A, Treisman R. Mutant actins demonstrate a role for unpolymerized actin in control of transcription by serum response factor. Mol Biol Cell 2002; 13:4167-78. [PMID: 12475943 PMCID: PMC138624 DOI: 10.1091/mbc.02-05-0068] [Citation(s) in RCA: 213] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
Signal-induced activation of the transcription factor serum response factor (SRF) requires alterations in actin dynamics. SRF activity can be inhibited by ectopic expression of beta-actin, either because actin itself participates in SRF regulation or as a consequence of cytoskeletal perturbations. To distinguish between these possibilities, we studied actin mutants. Three mutant actins, G13R, R62D, and a C-terminal VP16 fusion protein, were shown not to polymerize in vivo, as judged by two-hybrid, immunofluorescence, and cell fractionation studies. These actins effectively inhibited SRF activation, as did wild-type actin, which increased the G-actin level without altering the F:G-actin ratio. Physical interaction between SRF and actin was not detectable by mammalian or yeast two-hybrid assays, suggesting that SRF regulation involves an unidentified cofactor. SRF activity was not blocked upon inhibition of CRM1-mediated nuclear export by leptomycin B. Two actin mutants were identified, V159N and S14C, whose expression favored F-actin formation and which strongly activated SRF in the absence of external signals. These mutants seemed unable to inhibit SRF activity, because their expression did not reduce the absolute level of G-actin as assessed by DNase I binding. Taken together, these results provide strong evidence that G-actin, or a subpopulation of it, plays a direct role in signal transduction to SRF.
Collapse
Affiliation(s)
- Guido Posern
- Cancer Research UK London Research Institute, Lincoln's Inn Fields Laboratories, Transcription Laboratory, London WC2A 3PX, United Kingdom
| | | | | |
Collapse
|
25
|
Llorca O, Martín-Benito J, Gómez-Puertas P, Ritco-Vonsovici M, Willison KR, Carrascosa JL, Valpuesta JM. Analysis of the interaction between the eukaryotic chaperonin CCT and its substrates actin and tubulin. J Struct Biol 2001; 135:205-18. [PMID: 11580270 DOI: 10.1006/jsbi.2001.4359] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Two mechanisms have thus far been characterized for the assistance by chaperonins of the folding of other proteins. The first and best described is that of the prokaryotic chaperonin GroEL, which interacts with a large spectrum of proteins. GroEL uses a nonspecific mechanism by which any conformation of practically any unfolded polypeptide interacts with it through exposed, hydrophobic residues. ATP binding liberates the substrate in the GroEL cavity where it is given a chance to fold. A second mechanism has been described for the eukaryotic chaperonin CCT, which interacts mainly with the cytoskeletal proteins actin and tubulin. Cryoelectron microscopy and biochemical studies have revealed that both of these proteins interact with CCT in quasi-native, defined conformations. Here we have performed a detailed study of the docking of the actin and tubulin molecules extracted from their corresponding CCT:substrate complexes obtained from cryoelectron microscopy and image processing to localize certain regions in actin and tubulin that are involved in the interaction with CCT. These regions of actin and tubulin, which are not present in their prokaryotic counterparts FtsA and FtsZ, are involved in the polymerization of the two cytoskeletal proteins. These findings suggest coevolution of CCT with actin and tubulin in order to counteract the folding problems associated with the generation in these two cytoskeletal protein families of new domains involved in their polymerization.
Collapse
Affiliation(s)
- O Llorca
- Centro Nacional de Biotecnología, C.S.I.C., Campus Universidad Autónoma de Madrid, 28049, Spain
| | | | | | | | | | | | | |
Collapse
|