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Chang YC, Cao Z, Chen WT, Huang WC. Effects of stand-alone polar residue on membrane protein stability and structure. BIOCHIMICA ET BIOPHYSICA ACTA. BIOMEMBRANES 2024; 1866:184325. [PMID: 38653423 DOI: 10.1016/j.bbamem.2024.184325] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/29/2024] [Revised: 04/11/2024] [Accepted: 04/17/2024] [Indexed: 04/25/2024]
Abstract
Helical membrane proteins generally have a hydrophobic nature, with apolar side chains comprising the majority of the transmembrane (TM) helices. However, whenever polar side chains are present in the TM domain, they often exert a crucial role in structural interactions with other polar residues, such as TM helix associations and oligomerization. Moreover, polar residues in the TM region also often participate in protein functions, such as the Schiff base bonding between Lys residues and retinal in rhodopsin-like membrane proteins. Although many studies have focused on these functional polar residues, our understanding of stand-alone polar residues that are energetically unfavored in TM helixes is limited. Here, we adopted bacteriorhodopsin (bR) as a model system and systematically mutated 17 of its apolar Leu or Phe residues to polar Asn. Stability measurements of the resulting mutants revealed that all of these polar substitutions reduced bR stability to various extents, and the extent of destabilization of each mutant bR is also correlated to different structural factors, such as the relative accessible surface area and membrane depth of the mutation site. Structural analyses of these Asn residues revealed that they form sidechain-to-backbone hydrogen bonds that alleviate the unfavorable energetics in hydrophobic and apolar surroundings. Our results indicate that membrane proteins are able to accommodate certain stand-alone polar residues in the TM region without disrupting overall structures.
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Affiliation(s)
- Yu-Chu Chang
- Department of Biochemistry and Molecular Cell Biology, School of Medicine, College of Medicine, Taipei Medical University, Taipei, Taiwan; Graduate Institute of Medical Sciences, College of Medicine, Taipei Medical University, Taipei, Taiwan; International Ph.D. Program for Cell Therapy and Regeneration Medicine, College of Medicine, Taipei Medical University, Taipei, Taiwan.
| | - Zheng Cao
- Department of Chemistry and Biochemistry, Molecular Biology Institute, UCLA, Los Angeles, CA 90095, United States of America
| | - Wai-Ting Chen
- Department of Biochemistry and Molecular Cell Biology, School of Medicine, College of Medicine, Taipei Medical University, Taipei, Taiwan
| | - Wei-Chun Huang
- Department of Biochemistry and Molecular Cell Biology, School of Medicine, College of Medicine, Taipei Medical University, Taipei, Taiwan
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2
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Gupta S, Merriman C, Petzold CJ, Ralston CY, Fu D. Water molecules mediate zinc mobility in the bacterial zinc diffusion channel ZIPB. J Biol Chem 2019; 294:13327-13335. [PMID: 31320477 DOI: 10.1074/jbc.ra119.009239] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/07/2019] [Revised: 07/17/2019] [Indexed: 11/06/2022] Open
Abstract
Regulated ion diffusion across biological membranes is vital for cell function. In a nanoscale ion channel, the active role of discrete water molecules in modulating hydrodynamic behaviors of individual ions is poorly understood because of the technical challenge of tracking water molecules through the channel. Here we report the results of a hydroxyl radical footprinting analysis of the zinc-selective channel ZIPB from the Gram-negative bacterium, Bordetella bronchiseptica Irradiating ZIPB by microsecond X-ray pulses activated water molecules to form covalent hydroxyl radical adducts at nearby residues, which were identified by bottom-up proteomics to detect residues that interact either with zinc or water in response to zinc binding. We found a series of residues exhibiting reciprocal changes in water accessibility attributed to alternating zinc and water binding. Mapping these residues to the previously reported crystal structure of ZIPB, we identified a water-reactive pathway that superimposed on a zinc translocation pathway consisting of two binuclear metal centers and an interim zinc-binding site. The cotranslocation of zinc and water suggested that pore-lining residues undergo a mode switch between zinc coordination and water binding to confer zinc mobility. The unprecedented details of water-mediated zinc transport identified here highlight an essential role of solvated waters in driving zinc coordination dynamics and transmembrane crossing.
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Affiliation(s)
- Sayan Gupta
- Berkeley Center for Structural Biology, Molecular Biophysics and Integrated Bioimaging Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720
| | - Chengfeng Merriman
- Department of Physiology, Johns Hopkins School of Medicine, Baltimore, Maryland 21205
| | - Christopher J Petzold
- Biological Systems Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720; Engineering Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720
| | - Corie Y Ralston
- Berkeley Center for Structural Biology, Molecular Biophysics and Integrated Bioimaging Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720
| | - Dax Fu
- Department of Physiology, Johns Hopkins School of Medicine, Baltimore, Maryland 21205.
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Gupta S. Using X-ray Footprinting and Mass Spectrometry to Study the Structure and Function of Membrane Proteins. Protein Pept Lett 2019; 26:44-54. [PMID: 30484402 DOI: 10.2174/0929866526666181128142401] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2018] [Revised: 10/22/2018] [Accepted: 11/06/2018] [Indexed: 11/22/2022]
Abstract
BACKGROUND Membrane proteins are crucial for cellular sensory cascades and metabolite transport, and hence are key pharmacological targets. Structural studies by traditional highresolution techniques are limited by the requirements for high purity and stability when handled in high concentration and nonnative buffers. Hence, there is a growing requirement for the use of alternate methods in a complementary but orthogonal approach to study the dynamic and functional aspects of membrane proteins in physiologically relevant conditions. In recent years, significant progress has been made in the field of X-ray radiolytic labeling in combination with mass spectroscopy, commonly known as X-ray Footprinting and Mass Spectrometry (XFMS), which provide residue-specific information on the solvent accessibility of proteins. In combination with both lowresolution biophysical methods and high-resolution structural data, XFMS is capable of providing valuable insights into structure and dynamics of membrane proteins, which have been difficult to obtain by standalone high-resolution structural techniques. The XFMS method has also demonstrated a unique capability for identification of structural waters and their dynamics in protein cavities at both a high degree of spatial and temporal resolution, and thus capable of identifying conformational hot-spots in transmembrane proteins. CONCLUSION We provide a perspective on the place of XFMS amongst other structural biology methods and showcase some of the latest developments in its usage for studying conformational changes in membrane proteins.
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Affiliation(s)
- Sayan Gupta
- Molecular Biophysics and Integrated Bioimaging Division, Lawrence Berkeley National Laboratory, Berkeley, CA, United States
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Gupta S, Feng J, Chan LJG, Petzold CJ, Ralston CY. Synchrotron X-ray footprinting as a method to visualize water in proteins. JOURNAL OF SYNCHROTRON RADIATION 2016; 23:1056-69. [PMID: 27577756 PMCID: PMC5006651 DOI: 10.1107/s1600577516009024] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/30/2015] [Accepted: 06/03/2016] [Indexed: 05/23/2023]
Abstract
The vast majority of biomolecular processes are controlled or facilitated by water interactions. In enzymes, regulatory proteins, membrane-bound receptors and ion-channels, water bound to functionally important residues creates hydrogen-bonding networks that underlie the mechanism of action of the macromolecule. High-resolution X-ray structures are often difficult to obtain with many of these classes of proteins because sample conditions, such as the necessity of detergents, often impede crystallization. Other biophysical techniques such as neutron scattering, nuclear magnetic resonance and Fourier transform infrared spectroscopy are useful for studying internal water, though each has its own advantages and drawbacks, and often a hybrid approach is required to address important biological problems associated with protein-water interactions. One major area requiring more investigation is the study of bound water molecules which reside in cavities and channels and which are often involved in both the structural and functional aspects of receptor, transporter and ion channel proteins. In recent years, significant progress has been made in synchrotron-based radiolytic labeling and mass spectroscopy techniques for both the identification of bound waters and for characterizing the role of water in protein conformational changes at a high degree of spatial and temporal resolution. Here the latest developments and future capabilities of this method for investigating water-protein interactions and its synergy with other synchrotron-based methods are discussed.
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Affiliation(s)
- Sayan Gupta
- Molecular Biophysics and Integrated Bioimaging, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA
| | - Jun Feng
- Experimental Systems, Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA
| | - Leanne Jade G. Chan
- Biological Systems and Engineering, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA
| | - Christopher J. Petzold
- Biological Systems and Engineering, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA
| | - Corie Y. Ralston
- Molecular Biophysics and Integrated Bioimaging, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA
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Statistical survey of the buried waters in the Protein Data Bank. Amino Acids 2015; 48:193-202. [PMID: 26315961 DOI: 10.1007/s00726-015-2064-4] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/26/2015] [Accepted: 07/29/2015] [Indexed: 12/18/2022]
Abstract
The structures of buried water molecules were studied in an ensemble of high-quality and non-redundant protein crystal structures. Buried water molecules were clustered and classified in lake-like clusters, which are completely isolated from the bulk solvent, and bay-like clusters, which are in contact with the bulk solvent through a surface water molecule. Buried water molecules are extremely common: lake-like clusters are found in 89 % of the protein crystal structures and bay-like clusters in 93 %. Clusters with only one water molecule are much more common than larger clusters. Both cluster types incline to be surrounded by loop residues, and to a minor extent by residues in extended secondary structure. Helical residues on the contrary do not tend to surround clusters of buried water molecules. One buried water molecule is found every 30-50 amino acid residues, depending on the secondary structures that are more abundant in the protein. Both main- and side-chain atoms are in contact with buried waters; they form four hydrogen bonds with the first water and 1-1.5 additional hydrogen bond for each additional water in the cluster. Consequently, buried water molecules appear to be firmly packed and rigid like the protein atoms. In this regard, it is remarkable to observe that prolines often surround water molecules buried in the protein interior. Interestingly, clusters of buried water molecules tend to be just beneath the protein surface. Moreover, water molecules tend to form a one-dimensional wire rather than more compact arrangements. This agrees with recent evidence of the mechanisms of solvent exchange between internal cavities and bulk solvent.
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Abstract
Rhodopsin is a key light-sensitive protein expressed exclusively in rod photoreceptor cells of the retina. Failure to express this transmembrane protein causes a lack of rod outer segment formation and progressive retinal degeneration, including the loss of cone photoreceptor cells. Molecular studies of rhodopsin have paved the way to understanding a large family of cell-surface membrane proteins called G protein-coupled receptors (GPCRs). Work started on rhodopsin over 100 years ago still continues today with substantial progress made every year. These activities underscore the importance of rhodopsin as a prototypical GPCR and receptor required for visual perception-the fundamental process of translating light energy into a biochemical cascade of events culminating in vision.
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Affiliation(s)
- Lukas Hofmann
- Department of Pharmacology, School of Medicine, Case Western Reserve University, 10900 Euclid Ave., Cleveland, OH, 44106, USA
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Copper-transporting P-type ATPases use a unique ion-release pathway. Nat Struct Mol Biol 2013; 21:43-8. [PMID: 24317491 DOI: 10.1038/nsmb.2721] [Citation(s) in RCA: 82] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/23/2013] [Accepted: 10/11/2013] [Indexed: 11/09/2022]
Abstract
Heavy metals in cells are typically regulated by PIB-type ATPases. The first structure of the class, a Cu(+)-ATPase from Legionella pneumophila (LpCopA), outlined a copper transport pathway across the membrane, which was inferred to be occluded. Here we show by molecular dynamics simulations that extracellular water solvated the transmembrane (TM) domain, results indicative of a Cu(+)-release pathway. Furthermore, a new LpCopA crystal structure determined at 2.8-Å resolution, trapped in the preceding E2P state, delineated the same passage, and site-directed-mutagenesis activity assays support a functional role for the conduit. The structural similarities between the TM domains of the two conformations suggest that Cu(+)-ATPases couple dephosphorylation and ion extrusion differently than do the well-characterized PII-type ATPases. The ion pathway explains why certain Menkes' and Wilson's disease mutations impair protein function and points to a site for inhibitors targeting pathogens.
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Petruk AA, Varriale S, Coscia MR, Mazzarella L, Merlino A, Oreste U. The structure of the CD3 ζζ transmembrane dimer in POPC and raft-like lipid bilayer: a molecular dynamics study. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2013; 1828:2637-45. [PMID: 23896554 DOI: 10.1016/j.bbamem.2013.07.019] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/29/2013] [Revised: 07/05/2013] [Accepted: 07/16/2013] [Indexed: 12/15/2022]
Abstract
Plasma membrane lipids significantly affect assembly and activity of many signaling networks. The present work is aimed at analyzing, by molecular dynamics simulations, the structure and dynamics of the CD3 ζζ dimer in palmitoyl-oleoyl-phosphatidylcholine bilayer (POPC) and in POPC/cholesterol/sphingomyelin bilayer, which resembles the raft membrane microdomain supposed to be the site of the signal transducing machinery. Both POPC and raft-like environment produce significant alterations in structure and flexibility of the CD3 ζζ with respect to nuclear magnetic resonance (NMR) model: the dimer is more compact, its secondary structure is slightly less ordered, the arrangement of the Asp6 pair, which is important for binding to the Arg residue in the alpha chain of the T cell receptor (TCR), is stabilized by water molecules. Different interactions of charged residues with lipids at the lipid-cytoplasm boundary occur when the two environments are compared. Furthermore, in contrast to what is observed in POPC, in the raft-like environment correlated motions between transmembrane and cytoplasmic regions are observed. Altogether the data suggest that when the TCR complex resides in the raft domains, the CD3 ζζ dimer assumes a specific conformation probably necessary to the correct signal transduction.
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Affiliation(s)
- Ariel Alcides Petruk
- Instituto Superior de Investigaciones Biológicas (INSIBIO-CONICET), Chacabuco 461, S. M. de Tucumán, Tucumán T4000ILI, Argentina
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Padayatti PS, Wang L, Gupta S, Orban T, Sun W, Salom D, Jordan SR, Palczewski K, Chance MR. A hybrid structural approach to analyze ligand binding by the serotonin type 4 receptor (5-HT4). Mol Cell Proteomics 2013; 12:1259-71. [PMID: 23378516 DOI: 10.1074/mcp.m112.025536] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Hybrid structural methods have been used in recent years to understand protein-protein or protein-ligand interactions where high resolution crystallography or NMR data on the protein of interest has been limited. For G protein-coupled receptors (GPCRs), high resolution structures of native structural forms other than rhodopsin have not yet been achieved; gaps in our knowledge have been filled by creative crystallography studies that have developed stable forms of receptors by multiple means. The neurotransmitter serotonin (5-hydroxytryptamine) is a key GPCR-based signaling molecule affecting many physiological manifestations in humans ranging from mood and anxiety to bowel function. However, a high resolution structure of any of the serotonin receptors has not yet been solved. Here, we used structural mass spectrometry along with theoretical computations, modeling, and other biochemical methods to develop a structured model for human serotonin receptor subtype 4(b) in the presence and absence of its antagonist GR125487. Our data confirmed the overall structure predicted by the model and revealed a highly conserved motif in the ligand-binding pocket of serotonin receptors as an important participant in ligand binding. In addition, identification of waters in the transmembrane region provided clues as to likely paths mediating intramolecular signaling. Overall, this study reveals the potential of hybrid structural methods, including mass spectrometry, to probe physiological and functional GPCR-ligand interactions with purified native protein.
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Abstract
This Perspective is focused on amide groups of peptides interacting with water. The 2D IR spectroscopy has already enabled structural aspects of the peptide backbone to be determined through its ability to measure the coupling between different amide-I modes. Here we describe why nonlinear IR is emerging as the method of choice to examine the fast components of the water dynamics near peptides and how isotopically edited peptide links can be used to probe the local water at a residue level in proteins. This type of research necessarily involves an intimate mix of theory and experiment. The description of the results is underpinned by relatively well established quantum-statistical theories that describe the important manifestations of peptide vibrational frequency fluctuations.
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Affiliation(s)
- Ayanjeet Ghosh
- Department of Chemistry, University of Pennsylvania, Philadelphia, PA 19104-6323, USA
| | - Robin M. Hochstrasser
- Department of Chemistry, University of Pennsylvania, Philadelphia, PA 19104-6323, USA
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Yu H, Rick SW. Free Energy, Entropy, and Enthalpy of a Water Molecule in Various Protein Environments. J Phys Chem B 2010; 114:11552-60. [DOI: 10.1021/jp104209w] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Hongtao Yu
- Department of Chemistry, University of New Orleans, New Orleans, Louisiana 70148
| | - Steven W. Rick
- Department of Chemistry, University of New Orleans, New Orleans, Louisiana 70148
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Transmembrane helical domain of the cannabinoid CB1 receptor. Biophys J 2009; 96:3251-62. [PMID: 19383469 DOI: 10.1016/j.bpj.2008.12.3934] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2008] [Revised: 12/09/2008] [Accepted: 12/30/2008] [Indexed: 01/05/2023] Open
Abstract
Brain cannabinoid (CB(1)) receptors are G-protein coupled receptors and belong to the rhodopsin-like subfamily. A homology model of the inactive state of the CB(1) receptor was constructed using the x-ray structure of beta(2)-adrenergic receptor (beta(2)AR) as the template. We used 105 ns duration molecular-dynamics simulations of the CB(1) receptor embedded in a 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) bilayer to gain some insight into the structure and function of the CB(1) receptor. As judged from the root mean-square deviations combined with the detailed structural analyses, the helical bundle of the CB(1) receptor appears to be fully converged in 50 ns of the simulation. The results reveal that the helical bundle structure of the CB(1) receptor maintains a topology quite similar to the x-ray structures of G-protein coupled receptors overall. It is also revealed that the CB(1) receptor is stabilized by the formation of extensive, water-mediated H-bond networks, aromatic stacking interactions, and receptor-lipid interactions within the helical core region. It is likely that these interactions, which are often specific to functional motifs, including the S(N)LAxAD, D(E)RY, CWxP, and NPxxY motifs, are the molecular constraints imposed on the inactive state of the CB(1) receptor. It appears that disruption of these specific interactions is necessary to release the molecular constraints to achieve a conformational change of the receptor suitable for G-protein activation.
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