1
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Characterizations of a novel peptide encoded by a circular RNA using in-silico analyses. Biochem Biophys Res Commun 2022; 630:36-40. [PMID: 36137323 DOI: 10.1016/j.bbrc.2022.09.033] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/02/2022] [Accepted: 09/07/2022] [Indexed: 12/23/2022]
Abstract
CircRNAs have gained importance in recent times due to their involvement in gene regulation and also in the prognosis of cancer. Generally, the circRNA directly interact with miRNA or RNA binding proteins to exert their action, but some of them can be translated. These translated peptides often participate in the regulation of cellular processes. The circPPP1R12A translated peptide has been shown to influence the functioning of the Mst pathway. The Mst signaling is noteworthy for its role in the process of development, but it also has a function as a regulator of apoptosis, which is significant for regulation of cancer. Overexpression of this novel peptide deactivates the Mst signaling to induce the expression of the proliferative oncogene, Yap. Its molecular interaction with the molecules in the Mst pathway is hitherto unknown. In this short report we present our findings from in-silico studies the plausible structure of the peptide through bioinformatics and dynamics simulation studies. This is the first such report on the structure of the novel peptide encoded by circPPP1R12A, which could be important to predict in future its molecular interactions to understand its functionality.
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2
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Nakao H, Nakano M. Flip-Flop Promotion Mechanisms by Model Transmembrane Peptides. Chem Pharm Bull (Tokyo) 2022; 70:519-523. [DOI: 10.1248/cpb.c22-00133] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Affiliation(s)
- Hiroyuki Nakao
- Department of Biointerface Chemistry, Faculty of Pharmaceutical Sciences, University of Toyama
| | - Minoru Nakano
- Department of Biointerface Chemistry, Faculty of Pharmaceutical Sciences, University of Toyama
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3
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Mapping temperature-dependent conformational change in the voltage-sensing domain of an engineered heat-activated K + channel. Proc Natl Acad Sci U S A 2021; 118:2017280118. [PMID: 33782120 DOI: 10.1073/pnas.2017280118] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023] Open
Abstract
Temperature-dependent regulation of ion channel activity is critical for a variety of physiological processes ranging from immune response to perception of noxious stimuli. Our understanding of the structural mechanisms that underlie temperature sensing remains limited, in part due to the difficulty of combining high-resolution structural analysis with temperature stimulus. Here, we use NMR to compare the temperature-dependent behavior of Shaker potassium channel voltage sensor domain (WT-VSD) to its engineered temperature sensitive (TS-VSD) variant. Further insight into the molecular basis for temperature-dependent behavior is obtained by analyzing the experimental results together with molecular dynamics simulations. Our studies reveal that the overall secondary structure of the engineered TS-VSD is identical to the wild-type channels except for local changes in backbone torsion angles near the site of substitution (V369S and F370S). Remarkably however, these structural differences result in increased hydration of the voltage-sensing arginines and the S4-S5 linker helix in the TS-VSD at higher temperatures, in contrast to the WT-VSD. These findings highlight how subtle differences in the primary structure can result in large-scale changes in solvation and thereby confer increased temperature-dependent activity beyond that predicted by linear summation of solvation energies of individual substituents.
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4
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Yazdani M, Zhang G, Jia Z, Shi J, Cui J, Chen J. Aromatic interactions with membrane modulate human BK channel activation. eLife 2020; 9:55571. [PMID: 32597752 PMCID: PMC7371421 DOI: 10.7554/elife.55571] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/05/2020] [Accepted: 06/28/2020] [Indexed: 12/22/2022] Open
Abstract
Large-conductance potassium (BK) channels are transmembrane (TM) proteins that can be synergistically and independently activated by membrane voltage and intracellular Ca2+. The only covalent connection between the cytosolic Ca2+ sensing domain and the TM pore and voltage sensing domains is a 15-residue ‘C-linker’. To determine the linker’s role in human BK activation, we designed a series of linker sequence scrambling mutants to suppress potential complex interplay of specific interactions with the rest of the protein. The results revealed a surprising sensitivity of BK activation to the linker sequence. Combining atomistic simulations and further mutagenesis experiments, we demonstrated that nonspecific interactions of the linker with membrane alone could directly modulate BK activation. The C-linker thus plays more direct roles in mediating allosteric coupling between BK domains than previously assumed. Our results suggest that covalent linkers could directly modulate TM protein function and should be considered an integral component of the sensing apparatus.
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Affiliation(s)
- Mahdieh Yazdani
- Department of Chemistry, University of Massachusetts, Amherst, United States
| | - Guohui Zhang
- Department of Biomedical Engineering, Center for the Investigation of Membrane Excitability Disorders, Cardiac Bioelectricity and Arrhythmia Center, Washington University, St Louis, United States
| | - Zhiguang Jia
- Department of Chemistry, University of Massachusetts, Amherst, United States
| | - Jingyi Shi
- Department of Biomedical Engineering, Center for the Investigation of Membrane Excitability Disorders, Cardiac Bioelectricity and Arrhythmia Center, Washington University, St Louis, United States
| | - Jianmin Cui
- Department of Biomedical Engineering, Center for the Investigation of Membrane Excitability Disorders, Cardiac Bioelectricity and Arrhythmia Center, Washington University, St Louis, United States
| | - Jianhan Chen
- Department of Chemistry, University of Massachusetts, Amherst, United States.,Department of Biochemistry and Molecular Biology, University of Massachusetts, Amherst, United States
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5
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Maity A, Sinha S, Ghosh Dastidar S. Dissecting the thermodynamic contributions of the charged residues in the membrane anchoring of Bcl-xl C-terminal domain. Chem Phys Lipids 2018; 218:112-124. [PMID: 30550879 DOI: 10.1016/j.chemphyslip.2018.12.004] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2018] [Revised: 11/20/2018] [Accepted: 12/09/2018] [Indexed: 11/28/2022]
Abstract
The C-terminal helix of the Bcl-xl is known to initiate the membrane insertion of the protein by anchoring into the mitochondrial outer membrane. The C-terminal charged residues of that helix, R232 and K233, are reported to have an important structural role in the process of that insertion. The present work provides a quantitative understanding of the thermodynamic contribution of these residues on the membrane insertion energy-profile, calculated from the Adaptive Biasing Force based MD simulations of 2.67 μs altogether. Interestingly, the effect of the single neutralizing mutations at the C-terminus, i.e. K233A or R232A, is easily tolerated by the peptide without impacting the nature of insertion energy-profile, indicating the efficiency of one positively charged residue to drive the insertion. Whereas a double mutant, i.e. R232A and K233A, makes a significant impact on the energy-profile by destabilizing the membrane-associated states, as well as the membrane-embedded states. The finding provides molecular-level mechanistic insight. The water-mediated interaction formed by the peptide polar side chains within the bilayer core is found to modulate the membrane response during peptide insertion and that subsequently regulates the insertion mechanism. Mutation of the C-terminal residues eventually alters such a cascade of interactions that results in an insertion through energetically more expensive pathway. Since any one of the positively charged residues at the terminal is critical to ensure the membrane insertion, it appears that the natural selection of 'two' instead of 'one' charged residue is redundant in the context of membrane anchoring but may be important for other biochemical events.
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Affiliation(s)
- Atanu Maity
- Division of Bioinformatics, Bose Institute, P-1/12 C.I.T. Scheme VII M, Kolkata, 700054, India
| | - Souvik Sinha
- Division of Bioinformatics, Bose Institute, P-1/12 C.I.T. Scheme VII M, Kolkata, 700054, India
| | - Shubhra Ghosh Dastidar
- Division of Bioinformatics, Bose Institute, P-1/12 C.I.T. Scheme VII M, Kolkata, 700054, India.
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6
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Nakao H, Hayashi C, Ikeda K, Saito H, Nagao H, Nakano M. Effects of Hydrophilic Residues and Hydrophobic Length on Flip-Flop Promotion by Transmembrane Peptides. J Phys Chem B 2018; 122:4318-4324. [PMID: 29589918 DOI: 10.1021/acs.jpcb.8b00298] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
Peptide-induced phospholipid flip-flop (scrambling) was evaluated using transmembrane model peptides in which the central residue was substituted with various amino acid residues (sequence: Ac-GKK(LA) nXW(LA) nLKKA-CONH2). Peptides with a strongly hydrophilic residue (X = Q, N, or H) had higher scramblase activity than that of other peptides, and the activity was also dependent on the length of the peptides. Peptides with a hydrophobic stretch of 17 residues showed high flip-promotion propensity, whereas those of 21 and 25 residues did not, suggesting that membrane thinning under negative mismatch conditions promotes the flipping. Interestingly, a hydrophobic stretch of 19 residues intensively promoted phospholipid scrambling and membrane leakage. The distinctive characteristics of the peptide were ascribed by long-term molecular dynamics simulation to the arrangement of central glutamine and terminal four lysine residues on the same side of the helix. The combination of simulated and experimental data enables understanding of the mechanisms by which transmembrane helices, and ultimately unidentified scramblases in biomembranes, cause lipid scrambling.
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Affiliation(s)
- Hiroyuki Nakao
- Graduate School of Medicine and Pharmaceutical Sciences , University of Toyama , 2630 Sugitani , Toyama 930-0194 , Japan
| | - Chihiro Hayashi
- Graduate School of Medicine and Pharmaceutical Sciences , University of Toyama , 2630 Sugitani , Toyama 930-0194 , Japan
| | - Keisuke Ikeda
- Graduate School of Medicine and Pharmaceutical Sciences , University of Toyama , 2630 Sugitani , Toyama 930-0194 , Japan
| | - Hiroaki Saito
- Institute of Science and Engineering , Kanazawa University , Kakuma , Kanazawa , Ishikawa 920-1192 , Japan.,Laboratory for Computational Molecular Design , RIKEN Quantitative Biology Center , 6-2-4 Furuedai , Suita , Osaka 565-0874 , Japan
| | - Hidemi Nagao
- Institute of Science and Engineering , Kanazawa University , Kakuma , Kanazawa , Ishikawa 920-1192 , Japan
| | - Minoru Nakano
- Graduate School of Medicine and Pharmaceutical Sciences , University of Toyama , 2630 Sugitani , Toyama 930-0194 , Japan
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7
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Shrestha R, Anderson CM, Cardenas AE, Elber R, Webb LJ. Direct Measurement of the Effect of Cholesterol and 6-Ketocholestanol on the Membrane Dipole Electric Field Using Vibrational Stark Effect Spectroscopy Coupled with Molecular Dynamics Simulations. J Phys Chem B 2017; 121:3424-3436. [PMID: 28071910 PMCID: PMC5398937 DOI: 10.1021/acs.jpcb.6b09007] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
Biological membranes are heterogeneous structures with complex electrostatic profiles arising from lipids, sterols, membrane proteins, and water molecules. We investigated the effect of cholesterol and its derivative 6-ketocholestanol (6-kc) on membrane electrostatics by directly measuring the dipole electric field (F⃗d) within lipid bilayers containing cholesterol or 6-kc at concentrations of 0-40 mol% through the vibrational Stark effect (VSE). We found that adding low concentrations of cholesterol, up to ∼10 mol %, increases F⃗d, while adding more cholesterol up to 40 mol% lowers F⃗d. In contrast, we measured a monotonic increase in F⃗d as 6-kc concentration increased. We propose that this membrane electric field is affected by multiple factors: the polarity of the sterol molecules, the reorientation of the phospholipid dipole due to sterol, and the impact of the sterol on hydrogen bonding with surface water. We used molecular dynamics simulations to examine the distribution of phospholipids, sterol, and helix in bilayers containing these sterols. At low concentrations, we observed clustering of sterols near the vibrational probe whereas at high concentrations, we observed spatial correlation between the positions of the sterol molecules. This work demonstrates how a one-atom difference in a sterol changes the physicochemical and electric field properties of the bilayer.
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Affiliation(s)
- Rebika Shrestha
- Department of Chemistry, ‡Institute for Cell and Molecular Biology, §Center for Nano- and Molecular Science and Technology, and ∥Institute for Computational Engineering and Sciences, The University of Texas at Austin , Austin, Texas 78712, United States
| | - Cari M Anderson
- Department of Chemistry, ‡Institute for Cell and Molecular Biology, §Center for Nano- and Molecular Science and Technology, and ∥Institute for Computational Engineering and Sciences, The University of Texas at Austin , Austin, Texas 78712, United States
| | - Alfredo E Cardenas
- Department of Chemistry, ‡Institute for Cell and Molecular Biology, §Center for Nano- and Molecular Science and Technology, and ∥Institute for Computational Engineering and Sciences, The University of Texas at Austin , Austin, Texas 78712, United States
| | - Ron Elber
- Department of Chemistry, ‡Institute for Cell and Molecular Biology, §Center for Nano- and Molecular Science and Technology, and ∥Institute for Computational Engineering and Sciences, The University of Texas at Austin , Austin, Texas 78712, United States
| | - Lauren J Webb
- Department of Chemistry, ‡Institute for Cell and Molecular Biology, §Center for Nano- and Molecular Science and Technology, and ∥Institute for Computational Engineering and Sciences, The University of Texas at Austin , Austin, Texas 78712, United States
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8
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Rajagopalan V, Greathouse DV, Koeppe RE. Influence of glutamic acid residues and pH on the properties of transmembrane helices. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2017; 1859:484-492. [PMID: 28069412 DOI: 10.1016/j.bbamem.2017.01.006] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/31/2016] [Revised: 12/13/2016] [Accepted: 01/04/2017] [Indexed: 11/13/2022]
Abstract
Negatively charged side chains are important for the function of particular ion channels and certain other membrane proteins. To investigate the influence of single glutamic acid side chains on helices that span lipid-bilayer membranes, we have employed GWALP23 (acetyl-GGALW5LALALALALALALW19LAGA-amide) as a favorable host peptide framework. We substituted individual Leu residues with Glu residues (L12E or L14E or L16E) and incorporated specific 2H-labeled alanine residues within the core helical region or near the ends of the sequence. Solid-state 2H NMR spectra reveal little change for the core labels in GWALP23-E12, -E14 and -E16 over a pH range of 4 to 12.5, with the spectra being broader for samples in DOPC compared to DLPC bilayers. The spectra for samples with deuterium labels near the helix ends on alanines 3 and 21 show modest pH-dependent changes in the extent of unwinding of the helix terminals in DLPC and DOPC bilayers. The combined results indicate minor overall responses of these transmembrane helices to changes in pH, with the most buried residue E12 showing no pH dependence. While the Glu residues E14 and E16 may have high pKa values in the lipid bilayer environment, it is also possible that a paucity of helix response is masking the pKa values. Interestingly, when E16 is present, spectral changes at high pH report significant local unwinding of the core helix. Our results are consistent with the expectation that buried carboxyl groups aggressively hold their protons and/or waters of hydration.
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Affiliation(s)
- Venkatesan Rajagopalan
- Department of Chemistry and Biochemistry, University of Arkansas, Fayetteville, AR 72701, United States
| | - Denise V Greathouse
- Department of Chemistry and Biochemistry, University of Arkansas, Fayetteville, AR 72701, United States
| | - Roger E Koeppe
- Department of Chemistry and Biochemistry, University of Arkansas, Fayetteville, AR 72701, United States.
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9
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Inda ME, Oliveira RG, de Mendoza D, Cybulski LE. The Single Transmembrane Segment of Minimal Sensor DesK Senses Temperature via a Membrane-Thickness Caliper. J Bacteriol 2016; 198:2945-2954. [PMID: 27528507 PMCID: PMC5055599 DOI: 10.1128/jb.00431-16] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/06/2016] [Accepted: 08/08/2016] [Indexed: 02/07/2023] Open
Abstract
Thermosensors detect temperature changes and trigger cellular responses crucial for survival at different temperatures. The thermosensor DesK is a transmembrane (TM) histidine kinase which detects a decrease in temperature through its TM segments (TMS). Here, we address a key issue: how a physical stimulus such as temperature can be converted into a cellular response. We show that the thickness of Bacillus lipid membranes varies with temperature and that such variations can be detected by DesK with great precision. On the basis of genetic studies and measurements of in vitro activity of a DesK construct with a single TMS (minimal sensor DesK [MS-DesK]), reconstituted in liposomes, we propose an interplay mechanism directed by a conserved dyad, phenylalanine 8-lysine 10. This dyad is critical to anchor the only transmembrane segment of the MS-DesK construct to the extracellular water-lipid interphase and is required for the transmembrane segment of MS-DesK to function as a caliper for precise measurement of membrane thickness. The data suggest that positively charged lysine 10, which is located in the hydrophobic core of the membrane but is close to the water-lipid interface, pulls the transmembrane region toward the water phase to localize its charge at the interface. Nevertheless, the hydrophobic residue phenylalanine 8, located at the N-terminal extreme of the TMS, has a strong tendency to remain in the lipid phase, impairing access of lysine 10 to the water phase. The outcome of this interplay is a fine-tuned sensitivity to membrane thickness that elicits conformational changes that favor different signaling states of the protein. IMPORTANCE The ability to sense and respond to extracellular signals is essential for cell survival. One example is the cellular response to temperature variation. How do cells "sense" temperature changes? It has been proposed that the bacterial thermosensor DesK acts as a molecular caliper measuring membrane thickness variations that would occur as a consequence of temperature changes and activates a pathway to restore membrane fluidity at low temperature. Here, we demonstrated that membrane thickness variations do occur at physiological temperatures by directly measuring Bacillus lipid membrane thickness. We also dissected the N-terminal sensing motif of MS-DesK at the molecular-biophysical level and found that the dyad phenylalanine-lysine at the water-lipid phase is critical for achievement of a fine-tuned sensitivity to temperature.
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Affiliation(s)
- Maria E Inda
- Departamento de Microbiología, Facultad de Ciencias Bioquímicas y Farmacéuticas, Universidad Nacional de Rosario and Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Suipacha, Rosario, Argentina
| | - Rafael G Oliveira
- Centro de Investigaciones en Química Biológica de Córdoba, CIQUIBIC, CONICET, and Departamento de Química Biológica, Facultad de Ciencias Químicas, Universidad Nacional de Córdoba, Ciudad Universitaria, Córdoba, Argentina
| | - Diego de Mendoza
- Instituto de Biología Molecular y Celular de Rosario, CONICET, Universidad Nacional de Rosario, Predio CONICET, Rosario, Argentina
| | - Larisa E Cybulski
- Departamento de Microbiología, Facultad de Ciencias Bioquímicas y Farmacéuticas, Universidad Nacional de Rosario and Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Suipacha, Rosario, Argentina
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10
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Wood I, Pickholz M. Naratriptan aggregation in lipid bilayers: perspectives from molecular dynamics simulations. J Mol Model 2016; 22:221. [PMID: 27558798 DOI: 10.1007/s00894-016-3096-8] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2016] [Accepted: 08/08/2016] [Indexed: 11/27/2022]
Abstract
In order to understand the interaction between naratriptan and a fully hydrated bilayer of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphatidyl-choline (POPC), we carried out molecular dynamics simulations. The simulations were performed considering neutral and protonated ionization states, starting from different initial conditions. At physiological pH, the protonated state of naratriptan is predominant. It is expected that neutral compounds could have larger membrane partition than charged compounds. However, for the specific case of triptans, it is difficult to study neutral species in membranes experimentally, making computer simulations an interesting tool. When the naratriptan molecules were originally placed in water, they partitioned between the bilayer/water interface and water phase, as has been described for similar compounds. From this condition, the drugs displayed low access to the hydrophobic environment, with no significant effects on bilayer organization. The molecules anchored in the interface, due mainly to the barrier function of the polar and oriented lipid heads. On the other hand, when placed inside the bilayer, both neutral and protonated naratriptan showed self-aggregation in the lipid tail environment. In particular, the protonated species exhibited a pore-like structure, dragging water through this environment. Graphical Abstract Different behaviour of Naratriptan and Sumatriptan, when the drugs were originally placed in the lipid core.
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Affiliation(s)
- Irene Wood
- Instituto de Nanobiotecnología (NANOBIOTEC), Universidad de Buenos Aires, CONICET, Junin 956 CP 1113, Buenos Aires, Argentina.,National Science Research Council (CONICET), Buenos Aires, Argentina
| | - Mónica Pickholz
- Instituto de Nanobiotecnología (NANOBIOTEC), Universidad de Buenos Aires, CONICET, Junin 956 CP 1113, Buenos Aires, Argentina. .,National Science Research Council (CONICET), Buenos Aires, Argentina.
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11
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Abstract
A series of cyclic peptides containing a number of tryptophan (W) and glutamic acid (E) residues were synthesized and evaluated as pH-sensitive agents for targeting of acidic tissue and pH-dependent cytoplasmic delivery of molecules. Biophysical studies revealed the molecular mechanism of peptides action and localization within the lipid bilayer of the membrane at high and low pHs. The symmetric, c[(WE)4WC], and asymmetric, c[E4W5C], cyclic peptides translocated amanitin, a polar cargo molecule of similar size, across the lipid bilayer and induced cell death in a pH- and concentration-dependent manner. Fluorescently-labelled peptides were evaluated for targeting of acidic 4T1 mammary tumors in mice. The highest tumor to muscle ratio (5.6) was established for asymmetric cyclic peptide, c[E4W5C], at 24 hours after intravenous administration. pH-insensitive cyclic peptide c[R4W5C], where glutamic acid residues (E) were replaced by positively charged arginine residues (R), did not exhibit tumor targeting. We have introduced a novel class of cyclic peptides, which can be utilized as a new pH-sensitive tool in investigation or targeting of acidic tissue.
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12
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Teixeira VH, Vila-Viçosa D, Reis PBPS, Machuqueiro M. pKa Values of Titrable Amino Acids at the Water/Membrane Interface. J Chem Theory Comput 2016; 12:930-4. [DOI: 10.1021/acs.jctc.5b01114] [Citation(s) in RCA: 51] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Vitor H. Teixeira
- Centro de Química
e Bioquímica, Departamento de Química e Bioquímica,
Faculdade de Ciências, Universidade de Lisboa, 1749-016 Lisboa, Portugal
| | - Diogo Vila-Viçosa
- Centro de Química
e Bioquímica, Departamento de Química e Bioquímica,
Faculdade de Ciências, Universidade de Lisboa, 1749-016 Lisboa, Portugal
| | - Pedro B. P. S. Reis
- Centro de Química
e Bioquímica, Departamento de Química e Bioquímica,
Faculdade de Ciências, Universidade de Lisboa, 1749-016 Lisboa, Portugal
| | - Miguel Machuqueiro
- Centro de Química
e Bioquímica, Departamento de Química e Bioquímica,
Faculdade de Ciências, Universidade de Lisboa, 1749-016 Lisboa, Portugal
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13
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Maity A, Sinha S, Ganguly D, Ghosh Dastidar S. C-terminal tail insertion of Bcl-xL in membrane occurs via partial unfolding and refolding cycle associating microsolvation. Phys Chem Chem Phys 2016; 18:24095-105. [DOI: 10.1039/c6cp02468h] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
Insertion of the Bcl-xL C-terminal into the mitochondrial outer membrane is found to be guided by the partial unfolding–refolding cycle, assisted by micro-solvation.
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Affiliation(s)
- Atanu Maity
- Bioinformatics Centre
- Bose Institute
- P-1/12 CIT Scheme VII M
- Kolkata 700054
- India
| | - Souvik Sinha
- Bioinformatics Centre
- Bose Institute
- P-1/12 CIT Scheme VII M
- Kolkata 700054
- India
| | - Debabani Ganguly
- Department of Chemistry
- Indian Institute of Engineering Science and Technology
- Howrah-711103
- India
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14
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Rajapaksha SP, Pal N, Zheng D, Lu HP. Protein-fluctuation-induced water-pore formation in ion channel voltage-sensor translocation across a lipid bilayer membrane. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2015; 92:052719. [PMID: 26651735 DOI: 10.1103/physreve.92.052719] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/24/2015] [Indexed: 06/05/2023]
Abstract
We have applied a combined fluorescence microscopy and single-ion-channel electric current recording approach, correlating with molecular dynamics (MD) simulations, to study the mechanism of voltage-sensor domain translocation across a lipid bilayer. We use the colicin Ia ion channel as a model system, and our experimental and simulation results show the following: (1) The open-close activity of an activated colicin Ia is not necessarily sensitive to the amplitude of the applied cross-membrane voltage when the cross-membrane voltage is around the resting potential of excitable membranes; and (2) there is a significant probability that the activation of colicin Ia occurs by forming a transient and fluctuating water pore of ∼15 Å diameter in the lipid bilayer membrane. The location of the water-pore formation is nonrandom and highly specific, right at the insertion site of colicin Ia charged residues in the lipid bilayer membrane, and the formation is intrinsically associated with the polypeptide conformational fluctuations and solvation dynamics. Our results suggest an interesting mechanistic pathway for voltage-sensitive ion channel activation, and specifically for translocation of charged polypeptide chains across the lipid membrane under a transmembrane electric field: the charged polypeptide domain facilitates the formation of hydrophilic water pore in the membrane and diffuses through the hydrophilic pathway across the membrane; i.e., the charged polypeptide chain can cross a lipid membrane without entering into the hydrophobic core of the lipid membrane but entirely through the aqueous and hydrophilic environment to achieve a cross-membrane translocation. This mechanism sheds light on the intensive and fundamental debate on how a hydrophilic and charged peptide domain diffuses across the biologically inaccessible high-energy barrier of the hydrophobic core of a lipid bilayer: The peptide domain does not need to cross the hydrophobic core to move across a lipid bilayer.
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Affiliation(s)
- Suneth P Rajapaksha
- Department of Chemistry and Center for Photochemical Sciences, Bowling Green State University, Bowling Green, Ohio 43403, USA
| | - Nibedita Pal
- Department of Chemistry and Center for Photochemical Sciences, Bowling Green State University, Bowling Green, Ohio 43403, USA
| | - Desheng Zheng
- Department of Chemistry and Center for Photochemical Sciences, Bowling Green State University, Bowling Green, Ohio 43403, USA
| | - H Peter Lu
- Department of Chemistry and Center for Photochemical Sciences, Bowling Green State University, Bowling Green, Ohio 43403, USA
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15
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De Marothy MT, Elofsson A. Marginally hydrophobic transmembrane α-helices shaping membrane protein folding. Protein Sci 2015; 24:1057-74. [PMID: 25970811 DOI: 10.1002/pro.2698] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2015] [Accepted: 04/24/2015] [Indexed: 01/12/2023]
Abstract
Cells have developed an incredible machinery to facilitate the insertion of membrane proteins into the membrane. While we have a fairly good understanding of the mechanism and determinants of membrane integration, more data is needed to understand the insertion of membrane proteins with more complex insertion and folding pathways. This review will focus on marginally hydrophobic transmembrane helices and their influence on membrane protein folding. These weakly hydrophobic transmembrane segments are by themselves not recognized by the translocon and therefore rely on local sequence context for membrane integration. How can such segments reside within the membrane? We will discuss this in the light of features found in the protein itself as well as the environment it resides in. Several characteristics in proteins have been described to influence the insertion of marginally hydrophobic helices. Additionally, the influence of biological membranes is significant. To begin with, the actual cost for having polar groups within the membrane may not be as high as expected; the presence of proteins in the membrane as well as characteristics of some amino acids may enable a transmembrane helix to harbor a charged residue. The lipid environment has also been shown to directly influence the topology as well as membrane boundaries of transmembrane helices-implying a dynamic relationship between membrane proteins and their environment.
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Affiliation(s)
- Minttu T De Marothy
- Department of Biochemistry and Biophysics Science for Life Laboratory, Stockholm University, Solna, SE-171 21, Sweden
| | - Arne Elofsson
- Department of Biochemistry and Biophysics Science for Life Laboratory, Stockholm University, Solna, SE-171 21, Sweden
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16
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Shrestha R, Cardenas AE, Elber R, Webb LJ. Measurement of the membrane dipole electric field in DMPC vesicles using vibrational shifts of p-cyanophenylalanine and molecular dynamics simulations. J Phys Chem B 2015; 119:2869-76. [PMID: 25602635 DOI: 10.1021/jp511677j] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
The magnitude of the membrane dipole field was measured using vibrational Stark effect (VSE) shifts of nitrile oscillators placed on the unnatural amino acid p-cyanophenylalanine (p-CN-Phe) added to a peptide sequence at four unique positions. These peptides, which were based on a repeating alanine-leucine motif, intercalated into small unilamellar DMPC vesicles which formed an α-helix as confirmed by circular dichroic (CD) spectroscopy. Molecular dynamics simulations of the membrane-intercalated helix containing two of the nitrile probes, one near the headgroup region of the lipid (αLAX(25)) and one buried in the interior of the bilayer (αLAX(16)), were used to examine the structure of the nitrile with respect to the membrane normal, the assumed direction of the dipole field, by quantifying both a small tilt of the helix in the bilayer and conformational rotation of the p-CN-Phe side chain at steady state. Vibrational absorption energies of the nitrile oscillator at each position showed a systematic blue shift as the nitrile was stepped toward the membrane interior; for several different concentrations of peptide, the absorption energy of the nitrile located in the middle of the bilayer was ∼3 cm(-1) greater than that of the nitrile closest to the surface of the membrane. Taken together, the measured VSE shifts and nitrile orientations within the membrane resulted in an absolute magnitude of 8-11 MV/cm for the dipole field, at the high end of the range of possible values that have been accumulated from a variety of indirect measurements. Implications for this are discussed.
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Affiliation(s)
- Rebika Shrestha
- Department of Chemistry, ‡Institute for Cell and Molecular Biology, §Center for Nano- and Molecular Science and Technology, and ∥Institute for Computational Engineering and Sciences, The University of Texas at Austin , Austin, Texas 78712, United States
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17
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Porasso RD, Ale NM, Ciocco Aloia F, Masone D, Del Pópolo MG, Ben Altabef A, Gomez-Zavaglia A, Diaz SB, Vila JA. Interaction of glycine, lysine, proline and histidine with dipalmitoylphosphatidylcholine lipid bilayers: a theoretical and experimental study. RSC Adv 2015. [DOI: 10.1039/c5ra03236a] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
The interaction of unblocked glycine, lysine, proline and histidine with a DPPC bilayer was assessed using extensive atomistic molecular dynamics simulations.
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Affiliation(s)
- Rodolfo D. Porasso
- Instituto de Matemática Aplicada San Luis (IMASL)
- CONICET
- Universidad Nacional de San Luis
- Argentina
| | - Norma M. Ale
- Instituto de Química Física
- Facultad de Bioquímica, Química y Farmacia
- U. N. T
- San Lorenzo 456
- Argentina
| | - Facundo Ciocco Aloia
- CONICET
- Facultad de Ciencias Exactas y Naturales
- Universidad Nacional de Cuyo
- Mendoza
- Argentina
| | - Diego Masone
- CONICET
- Facultad de Ciencias Exactas y Naturales
- Universidad Nacional de Cuyo
- Mendoza
- Argentina
| | - Mario G. Del Pópolo
- CONICET
- Facultad de Ciencias Exactas y Naturales
- Universidad Nacional de Cuyo
- Mendoza
- Argentina
| | - Aida Ben Altabef
- Instituto de Química Física
- Facultad de Bioquímica, Química y Farmacia
- U. N. T
- San Lorenzo 456
- Argentina
| | - Andrea Gomez-Zavaglia
- Center for Research and Development in Food Cryotechnology (CIDCA, CCT-CONICET, La Plata)
- Argentina
| | - Sonia B. Diaz
- Instituto de Química Física
- Facultad de Bioquímica, Química y Farmacia
- U. N. T
- San Lorenzo 456
- Argentina
| | - Jorge A. Vila
- Instituto de Matemática Aplicada San Luis (IMASL)
- CONICET
- Universidad Nacional de San Luis
- Argentina
- Baker Laboratory of Chemistry and Chemical Biology
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18
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Ramakrishna S, Padhi S, Priyakumar UD. Modeling the structure of SARS 3a transmembrane protein using a minimum unfavorable contact approach. J CHEM SCI 2015; 127:2159-2169. [PMID: 32218650 PMCID: PMC7090505 DOI: 10.1007/s12039-015-0982-z] [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: 05/19/2015] [Revised: 09/02/2015] [Accepted: 09/04/2015] [Indexed: 12/11/2022]
Abstract
3a is an accessory protein from SARS coronavirus that is known to play a significant role in the proliferation of the virus by forming tetrameric ion channels. Although the monomeric units are known to consist of three transmembrane (TM) domains, there are no solved structures available for the complete monomer. The present study proposes a structural model for the transmembrane region of the monomer by employing our previously tested approach, which predicts potential orientations of TM α-helices by minimizing the unfavorable contact surfaces between the different TM domains. The best model structure comprising all three α-helices has been subjected to MD simulations to examine its quality. The TM bundle was found to form a compact and stable structure with significant intermolecular interactions. The structural features of the proposed model of 3a account for observations from previous experimental investigations on the activity of the protein. Further analysis indicates that residues from the TM2 and TM3 domains are likely to line the pore of the ion channel, which is in good agreement with a recent experimental study. In the absence of an experimental structure for the protein, the proposed structure can serve as a useful model for inferring structure-function relationships about the protein. The structure of the membrane protein 3a from SARS coronavirus is modeled using an approach that minimizes unfavorable contacts between transmembrane domains. A structure for a complete monomeric form of the protein thereby proposed is able to account for the behavior of the protein reported in previous experimental studies. ![]()
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Affiliation(s)
- S Ramakrishna
- Center for Computational Natural Sciences and Bioinformatics, International Institute of Information Technology, Hyderabad, 500 032 India
| | - Siladitya Padhi
- Center for Computational Natural Sciences and Bioinformatics, International Institute of Information Technology, Hyderabad, 500 032 India
| | - U Deva Priyakumar
- Center for Computational Natural Sciences and Bioinformatics, International Institute of Information Technology, Hyderabad, 500 032 India
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19
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Scharnagl C, Pester O, Hornburg P, Hornburg D, Götz A, Langosch D. Side-chain to main-chain hydrogen bonding controls the intrinsic backbone dynamics of the amyloid precursor protein transmembrane helix. Biophys J 2014; 106:1318-26. [PMID: 24655507 DOI: 10.1016/j.bpj.2014.02.013] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/24/2013] [Revised: 01/28/2014] [Accepted: 02/07/2014] [Indexed: 01/19/2023] Open
Abstract
Many transmembrane helices contain serine and/or threonine residues whose side chains form intrahelical H-bonds with upstream carbonyl oxygens. Here, we investigated the impact of threonine side-chain/main-chain backbonding on the backbone dynamics of the amyloid precursor protein transmembrane helix. This helix consists of a N-terminal dimerization region and a C-terminal cleavage region, which is processed by γ-secretase to a series of products. Threonine mutations within this transmembrane helix are known to alter the cleavage pattern, which can lead to early-onset Alzheimer's disease. Circular dichroism spectroscopy and amide exchange experiments of synthetic transmembrane domain peptides reveal that mutating threonine enhances the flexibility of this helix. Molecular dynamics simulations show that the mutations reduce intrahelical amide H-bonding and H-bond lifetimes. In addition, the removal of side-chain/main-chain backbonding distorts the helix, which alters bending and rotation at a diglycine hinge connecting the dimerization and cleavage regions. We propose that the backbone dynamics of the substrate profoundly affects the way by which the substrate is presented to the catalytic site within the enzyme. Changing this conformational flexibility may thus change the pattern of proteolytic processing.
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Affiliation(s)
| | - Oxana Pester
- Munich Center for Integrated Protein Science (CIPS(M)) at Lehrstuhl Chemie der Biopolymere, Technische Universität München, Freising, Germany
| | - Philipp Hornburg
- Fakultät für Physik E14, Technische Universität München, Freising, Germany
| | - Daniel Hornburg
- Fakultät für Physik E14, Technische Universität München, Freising, Germany
| | - Alexander Götz
- Munich Center for Integrated Protein Science (CIPS(M)) at Lehrstuhl Chemie der Biopolymere, Technische Universität München, Freising, Germany
| | - Dieter Langosch
- Munich Center for Integrated Protein Science (CIPS(M)) at Lehrstuhl Chemie der Biopolymere, Technische Universität München, Freising, Germany
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20
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Hausrath AC. Model for coupled insertion and folding of membrane-spanning proteins. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2014; 90:022707. [PMID: 25215758 DOI: 10.1103/physreve.90.022707] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/03/2014] [Indexed: 06/03/2023]
Abstract
Current understanding of the forces directing the folding of integral membrane proteins is very limited compared to the detailed picture available for water-soluble proteins. While mechanistic studies of the folding process in vitro have been conducted for only a small number of membrane proteins, the available evidence indicates that their folding process is thermodynamically driven like that of soluble proteins. In vivo, however, the majority of integral membrane proteins are installed in membranes by dedicated machinery, suggesting that the cellular systems may act to facilitate and regulate the spontaneous physical process of folding. Both the in vitro folding process and the in vivo pathway must navigate an energy landscape dominated by the energetically favorable burial of hydrophobic segments in the membrane interior and the opposition to folding due to the need for passage of polar segments across the membrane. This manuscript describes a simple, exactly solvable model which incorporates these essential features of membrane protein folding. The model is used to compare the folding time under conditions which depict both the in vitro and in vivo pathways. It is proposed that the cellular complexes responsible for insertion of membrane proteins act by lowering the energy barrier for passage of polar regions through the membrane, thereby allowing the chain to more rapidly achieve the folded state.
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Affiliation(s)
- Andrew C Hausrath
- Department of Chemistry and Biochemistry and Program in Applied Mathematics, University of Arizona, Tucson, Arizona 85721, USA
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21
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Lazaridis T, Leveritt JM, PeBenito L. Implicit membrane treatment of buried charged groups: application to peptide translocation across lipid bilayers. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2014; 1838:2149-59. [PMID: 24525075 DOI: 10.1016/j.bbamem.2014.01.015] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/13/2013] [Accepted: 01/10/2014] [Indexed: 01/06/2023]
Abstract
The energetic cost of burying charged groups in the hydrophobic core of lipid bilayers has been controversial, with simulations giving higher estimates than certain experiments. Implicit membrane approaches are usually deemed too simplistic for this problem. Here we challenge this view. The free energy of transfer of amino acid side chains from water to the membrane center predicted by IMM1 is reasonably close to all-atom free energy calculations. The shape of the free energy profile, however, for the charged side chains needs to be modified to reflect the all-atom simulation findings (IMM1-LF). Membrane thinning is treated by combining simulations at different membrane widths with an estimate of membrane deformation free energy from elasticity theory. This approach is first tested on the voltage sensor and the isolated S4 helix of potassium channels. The voltage sensor is stably inserted in a transmembrane orientation for both the original and the modified model. The transmembrane orientation of the isolated S4 helix is unstable in the original model, but a stable local minimum in IMM1-LF, slightly higher in energy than the interfacial orientation. Peptide translocation is addressed by mapping the effective energy of the peptide as a function of vertical position and tilt angle, which allows identification of minimum energy pathways and transition states. The barriers computed for the S4 helix and other experimentally studied peptides are low enough for an observable rate. Thus, computational results and experimental studies on the membrane burial of peptide charged groups appear to be consistent. This article is part of a Special Issue entitled: Interfacially Active Peptides and Proteins. Guest Editors: William C. Wimley and Kalina Hristova.
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Affiliation(s)
- Themis Lazaridis
- Department of Chemistry, City College of New York, 160 Convent Avenue, New York, NY 10031, USA.
| | - John M Leveritt
- Department of Chemistry, City College of New York, 160 Convent Avenue, New York, NY 10031, USA
| | - Leo PeBenito
- Department of Chemistry, City College of New York, 160 Convent Avenue, New York, NY 10031, USA
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22
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Pogorelov TV, Vermaas JV, Arcario MJ, Tajkhorshid E. Partitioning of amino acids into a model membrane: capturing the interface. J Phys Chem B 2014; 118:1481-92. [PMID: 24451004 PMCID: PMC3983343 DOI: 10.1021/jp4089113] [Citation(s) in RCA: 44] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
![]()
Energetics
of protein side chain partitioning between aqueous solution
and cellular membranes is of fundamental importance for correctly
capturing the membrane binding and specific protein–lipid interactions
of peripheral membrane proteins. We recently reported a highly mobile
membrane mimetic (HMMM) model that accelerates lipid dynamics by modeling
the membrane interior partially as a fluid organic solvent while retaining
a literal description of the lipid head groups and the beginning of
the tails. While the HMMM has been successfully applied to study spontaneous
insertion of a number of peripheral proteins into membranes, a quantitative
characterization of the energetics of membrane–protein interactions
in HMMM membranes has not been performed. We report here the free
energy profiles for partitioning of 10 protein side chain analogues
into a HMMM membrane. In the interfacial and headgroup regions of
the membrane, the side chain free energy profiles show excellent agreement
with profiles previously reported for conventional membranes with
full-tail lipids. In regions where the organic solvent is prevalent,
the increased dipole and fluidity of the solvent generally result
in a less accurate description, most notably overstabilization of
aromatic and polar amino acids. As an additional measure of the ability
of the HMMM model to describe membrane–protein interactions,
the water-to-membrane interface transfer energies were analyzed and
found to be in agreement with the previously reported experimental
and computational hydrophobicity scales. We discuss strengths and
weaknesses of HMMM in describing protein–membrane interactions
as well as further development of model membranes.
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Affiliation(s)
- Taras V Pogorelov
- Center for Biophysics and Computational Biology, School of Chemical Sciences, Departments of Chemistry and Biochemistry, College of Medicine, and Beckman Institute for Advanced Science and Technology, University of Illinois at Urbana-Champaign , Urbana, Illinois 61801, United States
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23
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Characterization of the water defect at the HIV-1 gp41 membrane spanning domain in bilayers with and without cholesterol using molecular simulations. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2014; 1838:1396-405. [PMID: 24440660 DOI: 10.1016/j.bbamem.2014.01.009] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/07/2013] [Revised: 12/24/2013] [Accepted: 01/08/2014] [Indexed: 12/23/2022]
Abstract
The membrane spanning domain (MSD) of human immunodeficiency virus 1 (HIV-1) envelope glycoprotein gp41 is important for fusion and infection. We used molecular dynamics (MD) simulations (3.4 μs total) to relate membrane and peptide properties that lead to water solvation of the α-helical gp41 MSD's midspan arginine in pure dipalmitoylphosphatidylcholine (DPPC) and in 50/50 DPPC/cholesterol membranes. We find that the midspan arginine is solvated by water that penetrates the inner leaflet, leading to a so-called water defect. The water defect is surprisingly robust across initial conditions and membrane compositions, but the presence of cholesterol modulates its behavior in several key ways. In the cholesterol-containing membranes, fluctuations in membrane thickness and water penetration depth are localized near the midspan arginine, and the MSD helices display a tightly regulated tilt angle. In the cholesterol-free membranes, thickness fluctuations are not as strongly correlated to the peptide position and tilt angles vary significantly depending on protein position relative to boundaries between domains of differing thickness. Cholesterol in an HIV-1 viral membrane is required for infection. Therefore, this work suggests that the colocalized water defect and membrane thickness fluctuations in cholesterol-containing viral membranes play an important role in fusion by bringing the membrane closer to a stability limit that must be crossed for fusion to occur.
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24
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González C, Baez-Nieto D, Valencia I, Oyarzún I, Rojas P, Naranjo D, Latorre R. K(+) channels: function-structural overview. Compr Physiol 2013; 2:2087-149. [PMID: 23723034 DOI: 10.1002/cphy.c110047] [Citation(s) in RCA: 143] [Impact Index Per Article: 13.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
Abstract
Potassium channels are particularly important in determining the shape and duration of the action potential, controlling the membrane potential, modulating hormone secretion, epithelial function and, in the case of those K(+) channels activated by Ca(2+), damping excitatory signals. The multiplicity of roles played by K(+) channels is only possible to their mammoth diversity that includes at present 70 K(+) channels encoding genes in mammals. Today, thanks to the use of cloning, mutagenesis, and the more recent structural studies using x-ray crystallography, we are in a unique position to understand the origins of the enormous diversity of this superfamily of ion channels, the roles they play in different cell types, and the relations that exist between structure and function. With the exception of two-pore K(+) channels that are dimers, voltage-dependent K(+) channels are tetrameric assemblies and share an extremely well conserved pore region, in which the ion-selectivity filter resides. In the present overview, we discuss in the function, localization, and the relations between function and structure of the five different subfamilies of K(+) channels: (a) inward rectifiers, Kir; (b) four transmembrane segments-2 pores, K2P; (c) voltage-gated, Kv; (d) the Slo family; and (e) Ca(2+)-activated SK family, SKCa.
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Affiliation(s)
- Carlos González
- Centro Interdisciplinario de Neurociencia de Valparaíso, Facultad de Ciencias, Universidad de Valparaíso, Valparaíso, Chile
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25
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Bonhenry D, Tarek M, Dehez F. Effects of Phospholipid Composition on the Transfer of a Small Cationic Peptide Across a Model Biological Membrane. J Chem Theory Comput 2013; 9:5675-84. [PMID: 26592298 DOI: 10.1021/ct400576e] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The transfer of a lysine amino acid analogue across phospholipid membrane models was investigated using molecular-dynamics simulations. The evolution of the protonation state of this small peptide as a function of its position inside the membrane was studied by determining the local pKa by means of free-energy calculations. Permeability and mean-first-passage time were evaluated and showed that the transfer occurs on the submillisecond time scale. Comparative studies were conducted to evaluate changes in the pKa arising from differences in the phospholipid chemical structure. We compared, hence, the effect of an ether vs an ester linkage of the lipid headgroup as well as linear vs branched lipid tails. The study reveals that protonated lysine residues can be buried further inside an ether lipid membrane than an ester lipid membrane, while branched lipids are found to stabilize less the charged form compared to their unbranched lipid chain counterparts.
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Affiliation(s)
- Daniel Bonhenry
- Université de Lorraine, SRSMC, UMR 7565 , Vandoeuvre-lès-Nancy, F-54500, France.,CNRS, SRSMC, UMR 7565 , Vandoeuvre-lès-Nancy, F-54500, France
| | - Mounir Tarek
- Université de Lorraine, SRSMC, UMR 7565 , Vandoeuvre-lès-Nancy, F-54500, France.,CNRS, SRSMC, UMR 7565 , Vandoeuvre-lès-Nancy, F-54500, France
| | - François Dehez
- Université de Lorraine, SRSMC, UMR 7565 , Vandoeuvre-lès-Nancy, F-54500, France.,CNRS, SRSMC, UMR 7565 , Vandoeuvre-lès-Nancy, F-54500, France
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26
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Similarities and differences of serotonin and its precursors in their interactions with model membranes studied by molecular dynamics simulation. J Mol Struct 2013. [DOI: 10.1016/j.molstruc.2013.04.011] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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27
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Alvares RD, Tulumello DV, Macdonald PM, Deber CM, Prosser RS. Effects of a polar amino acid substitution on helix formation and aggregate size along the detergent-induced peptide folding pathway. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2013; 1828:373-81. [DOI: 10.1016/j.bbamem.2012.09.024] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/13/2012] [Revised: 09/06/2012] [Accepted: 09/24/2012] [Indexed: 12/15/2022]
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28
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Nugent T, Jones DT. Membrane protein structural bioinformatics. J Struct Biol 2012; 179:327-37. [DOI: 10.1016/j.jsb.2011.10.008] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/13/2011] [Accepted: 10/25/2011] [Indexed: 10/15/2022]
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29
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Del Val C, White SH, Bondar AN. Ser/Thr motifs in transmembrane proteins: conservation patterns and effects on local protein structure and dynamics. J Membr Biol 2012; 245:717-30. [PMID: 22836667 DOI: 10.1007/s00232-012-9452-4] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/05/2012] [Accepted: 06/04/2012] [Indexed: 01/16/2023]
Abstract
We combined systematic bioinformatics analyses and molecular dynamics simulations to assess the conservation patterns of Ser and Thr motifs in membrane proteins, and the effect of such motifs on the structure and dynamics of α-helical transmembrane (TM) segments. We find that Ser/Thr motifs are often present in β-barrel TM proteins. At least one Ser/Thr motif is present in almost half of the sequences of α-helical proteins analyzed here. The extensive bioinformatics analyses and inspection of protein structures led to the identification of molecular transporters with noticeable numbers of Ser/Thr motifs within the TM region. Given the energetic penalty for burying multiple Ser/Thr groups in the membrane hydrophobic core, the observation of transporters with multiple membrane-embedded Ser/Thr is intriguing and raises the question of how the presence of multiple Ser/Thr affects protein local structure and dynamics. Molecular dynamics simulations of four different Ser-containing model TM peptides indicate that backbone hydrogen bonding of membrane-buried Ser/Thr hydroxyl groups can significantly change the local structure and dynamics of the helix. Ser groups located close to the membrane interface can hydrogen bond to solvent water instead of protein backbone, leading to an enhanced local solvation of the peptide.
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Affiliation(s)
- Coral Del Val
- Department of Computer Science and Artificial Intelligence, University of Granada, Granada, Spain.
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30
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Herrera FE, Bouchet A, Lairion F, Disalvo EA, Pantano S. Molecular Dynamics Study of the Interaction of Arginine with Phosphatidylcholine and Phosphatidylethanolamine Bilayers. J Phys Chem B 2012; 116:4476-83. [DOI: 10.1021/jp2096357] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Fernando E. Herrera
- Institut Pasteur de Montevideo, Calle Mataojo 2020. CP 11400 Montevideo,
Uruguay
- Consejo Nacional
de Investigaciones
Científicas y Técnicas (CONICET), Departamento de Física,
Facultad de Bioquímica y Ciencias Biológicas, Universidad Nacional del Litoral, C.C. 242, Ciudad
Universitaria, C.P. S3000ZAA, Santa Fe, Argentina
| | - Ana Bouchet
- Laboratorio de Fisicoquímica
de Membranas Lipídicas, Facultad de Farmacia y Bioquímica, Universidad de Buenos Aires, Junín 956 2°P
(1113), Buenos Aires, Argentina
| | - Fabiana Lairion
- Laboratorio de Fisicoquímica
de Membranas Lipídicas, Facultad de Farmacia y Bioquímica, Universidad de Buenos Aires, Junín 956 2°P
(1113), Buenos Aires, Argentina
| | - E. Aníbal Disalvo
- Laboratorio de Fisicoquímica
de Membranas Lipídicas, Facultad de Farmacia y Bioquímica, Universidad de Buenos Aires, Junín 956 2°P
(1113), Buenos Aires, Argentina
| | - Sergio Pantano
- Institut Pasteur de Montevideo, Calle Mataojo 2020. CP 11400 Montevideo,
Uruguay
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31
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Wang T, Bai J, Jiang X, Nienhaus GU. Cellular uptake of nanoparticles by membrane penetration: a study combining confocal microscopy with FTIR spectroelectrochemistry. ACS NANO 2012; 6:1251-9. [PMID: 22250809 DOI: 10.1021/nn203892h] [Citation(s) in RCA: 239] [Impact Index Per Article: 19.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/18/2023]
Abstract
It is well-known that nanomaterials are capable of entering living cells, often by utilizing the cells' endocytic mechanisms. Passive penetration of the lipid bilayer may, however, occur as an alternative process. Here we have focused on the passive transport of small nanoparticles across the plasma membranes of red blood cells, which are incapable of endocytosis. By using fluorescence microscopy, we have observed that zwitterionic quantum dots penetrate through the cell membranes so that they can be found inside the cells. The penetration-induced structural changes of the lipid bilayer were explored by surface-enhanced infrared absorption spectroscopy and electrochemistry studies of model membranes prepared on solid supports with lipid compositions identical to those of red blood cell membranes. A detailed analysis of the infrared spectra revealed a markedly enhanced flexibility of the lipid bilayers in the presence of nanoparticles. The electrochemistry data showed that the overall membrane structure remained intact; however, no persistent holes were formed in the bilayers.
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Affiliation(s)
- Tiantian Wang
- State Key Laboratory of Electroanalytical Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun 130022, China
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32
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Ng DP, Poulsen BE, Deber CM. Membrane protein misassembly in disease. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2011; 1818:1115-22. [PMID: 21840297 DOI: 10.1016/j.bbamem.2011.07.046] [Citation(s) in RCA: 67] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/10/2011] [Revised: 07/28/2011] [Accepted: 07/29/2011] [Indexed: 11/19/2022]
Abstract
Helix-helix interactions play a central role in the folding and assembly of integral α-helical membrane proteins and are fundamentally dictated by the amino acid sequence of the TM domain. It is not surprising then that missense mutations that target these residues are often linked to disease. In this review, we focus on the molecular mechanisms through which missense mutations lead to aberrant folding and/or assembly of these proteins, and then discuss pharmacological approaches that may potentially mitigate or reverse the negative effects of these mutations. Improving our understanding of how missense mutations affect the interactions between TM α-helices will increase our capability to develop effective therapeutic approaches to counter the misassembly of these proteins and, ultimately, disease. This article is part of a Special Issue entitled: Protein Folding in Membranes.
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Affiliation(s)
- Derek P Ng
- Division of Molecular Structure & Function, Research Institute, Hospital for Sick Children, Toronto, Ontario, Canada
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33
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Fleming PJ, Freites JA, Moon CP, Tobias DJ, Fleming KG. Outer membrane phospholipase A in phospholipid bilayers: a model system for concerted computational and experimental investigations of amino acid side chain partitioning into lipid bilayers. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2011; 1818:126-34. [PMID: 21816133 DOI: 10.1016/j.bbamem.2011.07.016] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/01/2011] [Revised: 07/07/2011] [Accepted: 07/09/2011] [Indexed: 12/21/2022]
Abstract
Understanding the forces that stabilize membrane proteins in their native states is one of the contemporary challenges of biophysics. To date, estimates of side chain partitioning free energies from water to the lipid environment show disparate values between experimental and computational measures. Resolving the disparities is particularly important for understanding the energetic contributions of polar and charged side chains to membrane protein function because of the roles these residue types play in many cellular functions. In general, computational free energy estimates of charged side chain partitioning into bilayers are much larger than experimental measurements. However, the lack of a protein-based experimental system that uses bilayers against which to vet these computational predictions has traditionally been a significant drawback. Moon & Fleming recently published a novel hydrophobicity scale that was derived experimentally by using a host-guest strategy to measure the side chain energetic perturbation due to mutation in the context of a native membrane protein inserted into a phospholipid bilayer. These values are still approximately an order of magnitude smaller than computational estimates derived from molecular dynamics calculations from several independent groups. Here we address this discrepancy by showing that the free energy differences between experiment and computation become much smaller if the appropriate comparisons are drawn, which suggests that the two fields may in fact be converging. In addition, we present an initial computational characterization of the Moon & Fleming experimental system used for the hydrophobicity scale: OmpLA in DLPC bilayers. The hydrophobicity scale used OmpLA position 210 as the guest site, and our preliminary results demonstrate that this position is buried in the center of the DLPC membrane, validating its usage in the experimental studies. We further showed that the introduction of charged Arg at position 210 is well tolerated in OmpLA and that the DLPC bilayers accommodate this perturbation by creating a water dimple that allows the Arg side chain to remain hydrated. Lipid head groups visit the dimple and can hydrogen bond with Arg, but these interactions are transient. Overall, our study demonstrates the unique advantages of this molecular system because it can be interrogated by both computational and experimental practitioners, and it sets the stage for free energy calculations in a system for which there is unambiguous experimental data. This article is part of a Special Issue entitled: Membrane protein structure and function.
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Affiliation(s)
- Patrick J Fleming
- T. C. Jenkins Department of Biophysics, Johns Hopkins University, 3400 North Charles Street, Baltimore, MD 21218, USA
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34
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Tulumello DV, Deber CM. Positions of polar amino acids alter interactions between transmembrane segments and detergents. Biochemistry 2011; 50:3928-35. [PMID: 21473646 DOI: 10.1021/bi200238g] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
α-Helical transmembrane (TM) segments in membrane proteins are comprised primarily of hydrophobic amino acids that accommodate insertion from water into the nonpolar membrane bilayer. In many such segments, however, polar residues are also present for structural or functional reasons. These latter residues impair the local favorable acyl interactions required for solvation by hydrophobic media such as phospholipids in native bilayers or detergents used for in vitro characterization. Using a series of Lys-tagged designed TM-like peptides (typified by KK-YAAAIAAIAWAIAAIAAAIAA-KKK) in which single-Asn residue substitutions (from Ile or Ala) were made successively from the center of the hydrophobic region toward the C-terminus, we demonstrate that polar residues strongly alter the nature of the interaction between TM segments and the solvating detergent. Through the application of sodium dodecyl sulfate-polyacrylamide gel electrophoresis, circular dichroism spectroscopy, and tryptophan fluorescence, we observed drastic differences in the structures of the detergent-peptide complexes that contain relatively minor sequence differences. For example, the blue shift of the Trp fluorescence (indicating local detergent solvation at this location) differs by as much as ~10 nm depending upon the position of a single Asn substitution in an otherwise identical segment. The overall results suggest that polar point mutations occurring in a biological membrane will elicit comparable effects, placing a significant refolding burden on the local protein structure and potentially leading to disease states through altered protein--lipid interactions in membrane proteins.
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Affiliation(s)
- David V Tulumello
- Division of Molecular Structure and Function, Research Institute, Hospital for Sick Children, Toronto, Ontario, Canada M5G 1X8
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35
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Residue-specific side-chain packing determines the backbone dynamics of transmembrane model helices. Biophys J 2011; 99:2541-9. [PMID: 20959095 DOI: 10.1016/j.bpj.2010.08.031] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2010] [Revised: 07/06/2010] [Accepted: 08/12/2010] [Indexed: 12/28/2022] Open
Abstract
The transmembrane domains (TMDs) of membrane-fusogenic proteins contain an overabundance of β-branched residues. In a previous effort to systematically study the relation among valine content, fusogenicity, and helix dynamics, we developed model TMDs that we termed LV-peptides. The content and position of valine in LV-peptides determine their fusogenicity and backbone dynamics, as shown experimentally. Here, we analyze their conformational dynamics and the underlying molecular forces using molecular-dynamics simulations. Our study reveals that backbone dynamics is correlated with the efficiency of side-chain to side-chain van der Waals packing between consecutive turns of the helix. Leu side chains rapidly interconvert between two rotameric states, thus favoring contacts to its i±3 and i±4 neighbors. Stereochemical restraints acting on valine side chains in the α-helix force both β-substituents into an orientation where i,i±3 interactions are less favorable than i,i±4 interactions, thus inducing a local packing deficiency at VV3 motifs. We provide a quantitative molecular model to explain the relationship among chain connectivity, side-chain mobility, and backbone flexibility. We expect that this mechanism also defines the backbone flexibility of natural TMDs.
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36
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Jusoh SA, Helms V. Helical integrity and microsolvation of transmembrane domains from Flaviviridae envelope glycoproteins. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2011; 1808:1040-9. [PMID: 21223949 DOI: 10.1016/j.bbamem.2011.01.004] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/10/2010] [Revised: 11/23/2010] [Accepted: 01/04/2011] [Indexed: 01/24/2023]
Abstract
Charged and polar amino acids in the transmembrane domains of integral membrane proteins can be crucial for protein function and also promote helix-helix association or protein oligomerization. Yet, our current understanding is still limited on how these hydrophilic amino acids are efficiently translocated from the Sec61/SecY translocon into the cell membrane during the biogenesis of membrane proteins. In hepatitis C virus, the putative transmembrane segments of envelope glycoproteins E1 and E2 were suggested to heterodimerize via a Lys-Asp ion-pair in the host endoplasmic reticulum. Therefore in this work, we carried out molecular dynamic simulations in explicit lipid bilayer and solvent environment to explore the stability of all possible bridging ion-pairs using the model of H-segment helix dimers. We observed that, frequently, several water molecules penetrated from the interface into the membrane core to stabilize the charged and polar pairs. The hydration time and amount of water molecules in the membrane core depended on the position of the charged residues as well as on the type of ion-pairs. Similar microsolvation events were observed in simulations of the putative E1-E2 transmembrane helix dimers. Simulations of helix monomers from other members of the Flaviviridae family suggest that these systems show similar behaviors. Thus this study illustrates the important contribution of water microsolvation to overcome the unfavorable energetic cost of burying charged and polar amino acids in membrane lipid bilayers. Also, it emphasizes the novel role of bridging charged or polar interactions stabilized by water molecules in the hydrophobic lipid bilayer core that has an important biological function for helix dimerization in several envelope glycoproteins from the family of Flaviviridae viruses.
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Ulmschneider JP, Andersson M, Ulmschneider MB. Determining peptide partitioning properties via computer simulation. J Membr Biol 2010; 239:15-26. [PMID: 21107546 PMCID: PMC3030940 DOI: 10.1007/s00232-010-9324-8] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/2010] [Accepted: 11/05/2010] [Indexed: 11/24/2022]
Abstract
The transfer of polypeptide segments into lipid bilayers to form transmembrane helices represents the crucial first step in cellular membrane protein folding and assembly. This process is driven by complex and poorly understood atomic interactions of peptides with the lipid bilayer environment. The lack of suitable experimental techniques that can resolve these processes both at atomic resolution and nanosecond timescales has spurred the development of computational techniques. In this review, we summarize the significant progress achieved in the last few years in elucidating the partitioning of peptides into lipid bilayer membranes using atomic detail molecular dynamics simulations. Indeed, partitioning simulations can now provide a wealth of structural and dynamic information. Furthermore, we show that peptide-induced bilayer distortions, insertion pathways, transfer free energies, and kinetic insertion barriers are now accurate enough to complement experiments. Further advances in simulation methods and force field parameter accuracy promise to turn molecular dynamics simulations into a powerful tool for investigating a wide range of membrane active peptide phenomena.
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Illergård K, Kauko A, Elofsson A. Why are polar residues within the membrane core evolutionary conserved? Proteins 2010; 79:79-91. [PMID: 20938980 DOI: 10.1002/prot.22859] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/07/2010] [Revised: 07/23/2010] [Accepted: 08/13/2010] [Indexed: 11/08/2022]
Abstract
Here, we present a study of polar residues within the membrane core of alpha-helical membrane proteins. As expected, polar residues are less frequent in the membrane than expected. Further, most of these residues are buried within the interior of the protein and are only rarely exposed to lipids. However, the polar groups often border internal water filled cavities, even if the rest of the sidechain is buried. A survey of their functional roles in known structures showed that the polar residues are often directly involved in binding of small compounds, especially in channels and transporters, but other functions including proton transfer, catalysis, and selectivity have also been attributed to these proteins. Among the polar residues histidines often interact with prosthetic groups in photosynthetic- and oxidoreductase-related proteins, whereas prolines often are required for conformational changes of the proteins. Indeed, the polar residues in the membrane core are more conserved than other residues in the core, as well as more conserved than polar residues outside the membrane. The reason is twofold; they are often (i) buried in the interior of the protein and (ii) directly involved in the function of the proteins. Finally, a method to identify which polar residues are present within the membrane core directly from protein sequences was developed. Applying the method to the set of all human membrane proteins the prediction indicates that polar residues were most frequent among active transporter proteins and GPCRs, whereas infrequent in families with few transmembrane regions, such as non-GPCR receptors.
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Affiliation(s)
- Kristoffer Illergård
- Department of Biochemistry and Biophysics, Center for Biomembrane Research, Stockholm bioinformatics Center, Stockholm University, SE-106 91 Stockholm, Sweden
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39
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Electrostatics of deformable lipid membranes. Biophys J 2010; 98:2904-13. [PMID: 20550903 DOI: 10.1016/j.bpj.2010.03.046] [Citation(s) in RCA: 43] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/2010] [Revised: 03/17/2010] [Accepted: 03/19/2010] [Indexed: 11/20/2022] Open
Abstract
It was recently demonstrated that significant local deformations of biological membranes take place due to the fields of charged peptides and ions, challenging the standard model of membrane electrostatics. The ability of ions to retain their immediate hydration environment, combined with the lack of sensitivity of permeability to ion type or even ion pairs, led us to question the extent to which hydration energetics and electrostatics control membrane ion permeation. Using the arginine analog methyl-guanidinium as a test case, we find that although hydrocarbon electronic polarizability causes dramatic changes in ion solvation free energy, as well as a significant change (approximately 0.4 V) in the membrane dipole potential, little change in membrane permeation energetics occurs. We attribute this to compensation of solvation terms from polar and polarizable nonpolar components within the membrane, and explain why the dipole potential is not fully sensed in terms of the locally deformed bilayer interface. Our descriptions provide a deeper understanding of the translocation process and allow predictions for poly-ions, ion pairs, charged lipids, and lipid flip-flop. We also report simulations of large hydrophobic-ion-like membrane defects and the ionophore valinomycin, which exhibit little membrane deformation, as well as hydrophilic defects and the ion channel gramicidin A, to provide parallels to membranes deformed by unassisted ion permeation.
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40
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Gurtovenko AA, Anwar J, Vattulainen I. Defect-Mediated Trafficking across Cell Membranes: Insights from in Silico Modeling. Chem Rev 2010; 110:6077-103. [DOI: 10.1021/cr1000783] [Citation(s) in RCA: 158] [Impact Index Per Article: 11.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Affiliation(s)
- Andrey A. Gurtovenko
- Institute of Macromolecular Compounds, Russian Academy of Sciences, Bolshoi Prospect 31, V.O., St. Petersburg, 199004 Russia, Computational Laboratory, Institute of Pharmaceutical Innovation, University of Bradford, Bradford, West Yorkshire BD7 1DP, U.K., Department of Physics, Tampere University of Technology, P.O. Box 692, FI-33101 Tampere, Finland, Aalto University, School of Science and Technology, Finland, and MEMPHYS—Center for Biomembrane Physics, University of Southern Denmark, Odense, Denmark
| | - Jamshed Anwar
- Institute of Macromolecular Compounds, Russian Academy of Sciences, Bolshoi Prospect 31, V.O., St. Petersburg, 199004 Russia, Computational Laboratory, Institute of Pharmaceutical Innovation, University of Bradford, Bradford, West Yorkshire BD7 1DP, U.K., Department of Physics, Tampere University of Technology, P.O. Box 692, FI-33101 Tampere, Finland, Aalto University, School of Science and Technology, Finland, and MEMPHYS—Center for Biomembrane Physics, University of Southern Denmark, Odense, Denmark
| | - Ilpo Vattulainen
- Institute of Macromolecular Compounds, Russian Academy of Sciences, Bolshoi Prospect 31, V.O., St. Petersburg, 199004 Russia, Computational Laboratory, Institute of Pharmaceutical Innovation, University of Bradford, Bradford, West Yorkshire BD7 1DP, U.K., Department of Physics, Tampere University of Technology, P.O. Box 692, FI-33101 Tampere, Finland, Aalto University, School of Science and Technology, Finland, and MEMPHYS—Center for Biomembrane Physics, University of Southern Denmark, Odense, Denmark
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Jusoh SA, Welsch C, Siu SWI, Böckmann RA, Helms V. Contribution of charged and polar residues for the formation of the E1-E2 heterodimer from Hepatitis C Virus. J Mol Model 2010; 16:1625-37. [PMID: 20195665 DOI: 10.1007/s00894-010-0672-1] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/24/2009] [Accepted: 01/25/2010] [Indexed: 02/05/2023]
Abstract
The transmembrane domains of the envelope glycoprotein E1 and E2 have crucial multifunctional roles in the biogenesis of hepatitis C virus. We have performed molecular dynamics simulations to investigate a structural model of the transmembrane segments of the E1-E2 heterodimer. The simulations support the key role of the Lys370-Asp728 ion pair for mediating the E1-E2 heterodimerization. In comparison to these two residues, the simulation results also reveal the differential effect of the conserved Arg730 residue that has been observed in experimental studies. Furthermore, we discovered the formation of inter-helical hydrogen bonds via Asn367 that stabilize dimer formation. Simulations of single and double mutants further demonstrate the importance of the ion-pair and polar interactions between the interacting helix monomers. The conformation of the E1 fragment in the simulation of the E1-E2 heterodimer is in close agreement with an NMR structure of the E1 transmembrane segment. The proposed model of the E1-E2 heterodimer supports the postulated cooperative insertion of both helices by the translocon complex into the bilayer.
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Affiliation(s)
- Siti Azma Jusoh
- Center for Bioinformatics, Saarland University, 66041, Saarbruecken, Germany
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42
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Reduced voltage sensitivity in a K+-channel voltage sensor by electric field remodeling. Proc Natl Acad Sci U S A 2010; 107:5178-83. [PMID: 20194763 DOI: 10.1073/pnas.1000963107] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022] Open
Abstract
Propagation of the nerve impulse relies on the extreme voltage sensitivity of Na(+) and K(+) channels. The transmembrane movement of four arginine residues, located at the fourth transmembrane segment (S4), in each of their four voltage-sensing domains is mostly responsible for the translocation of 12 to 13 e(o) across the transmembrane electric field. Inserting additional positively charged residues between the voltage-sensing arginines in S4 would, in principle, increase voltage sensitivity. Here we show that either positively or negatively charged residues added between the two most external sensing arginines of S4 decreased voltage sensitivity of a Shaker voltage-gated K(+)-channel by up to approximately 50%. The replacement of Val363 with a charged residue displaced inwardly the external boundaries of the electric field by at least 6 A, leaving the most external arginine of S4 constitutively exposed to the extracellular space and permanently excluded from the electric field. Both the physical trajectory of S4 and its electromechanical coupling to open the pore gate seemed unchanged. We propose that the separation between the first two sensing charges at resting is comparable to the thickness of the low dielectric transmembrane barrier they must cross. Thus, at most a single sensing arginine side chain could be found within the field. The conserved hydrophobic nature of the residues located between the voltage-sensing arginines in S4 may shape the electric field geometry for optimal voltage sensitivity in voltage-gated ion channels.
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43
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Pantano DA, Klein ML. Characterization of membrane-protein interactions for the leucine transporter from Aquifex aeolicus by molecular dynamics calculations. J Phys Chem B 2010; 113:13715-22. [PMID: 19445452 DOI: 10.1021/jp901840u] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Multinanosecond molecular dynamics (MD) simulations have been employed to characterize the interaction of an integral membrane protein (IMP), the leucine transmitter from Aquifex aeolicus (Yamashita et al., Nature 2005, 437, 215-223), with hydrated lipid bilayer membranes in their physiologically relevant liquid crystalline phases. Analysis of the MD trajectories for dimyristoyl phosphatidylcholine (DMPC), 1-palmitoyl-2-oleoyl phosphatidylcholine (POPC), and 1-palmitoyl-2-oleoyl phosphatidylethanolamine (POPE) focused on the contacts between aromatic and basic side chains of the IMP with the lipid head groups and water. Structural fluctuations of the IMP were investigated as well as the contact dynamics of neighboring lipids. In characterizing the IMP-membrane systems, the behaviors of the protein's cytoplasmic and periplasmic parts are considered separately. All three lipid membranes show a rather similar overall level of association with the IMP. However, for DMPC there is a better matching of the membrane core to the hydrophobic transmembrane portion of the IMP. The closed cytoplasmic end of the IMP exhibits a higher degree of association with lipids than the more open periplasmic end, an observation which correlates with the more compact structure and a slower dynamics of surrounding lipids.
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Affiliation(s)
- Diego A Pantano
- Center for Molecular Modeling, Department of Chemistry, University of Pennsylvania, 231 S. 34th Street, Philadelphia, Pennsylvania 19104-6323, USA.
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44
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Hedin LE, Ojemalm K, Bernsel A, Hennerdal A, Illergård K, Enquist K, Kauko A, Cristobal S, von Heijne G, Lerch-Bader M, Nilsson I, Elofsson A. Membrane insertion of marginally hydrophobic transmembrane helices depends on sequence context. J Mol Biol 2009; 396:221-9. [PMID: 19931281 DOI: 10.1016/j.jmb.2009.11.036] [Citation(s) in RCA: 76] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/23/2009] [Revised: 11/11/2009] [Accepted: 11/13/2009] [Indexed: 11/25/2022]
Abstract
In mammalian cells, most integral membrane proteins are initially inserted into the endoplasmic reticulum membrane by the so-called Sec61 translocon. However, recent predictions suggest that many transmembrane helices (TMHs) in multispanning membrane proteins are not sufficiently hydrophobic to be recognized as such by the translocon. In this study, we have screened 16 marginally hydrophobic TMHs from membrane proteins of known three-dimensional structure. Indeed, most of these TMHs do not insert efficiently into the endoplasmic reticulum membrane by themselves. To test if loops or TMHs immediately upstream or downstream of a marginally hydrophobic helix might influence the insertion efficiency, insertion of marginally hydrophobic helices was also studied in the presence of their neighboring loops and helices. The results show that flanking loops and nearest-neighbor TMHs are sufficient to ensure the insertion of many marginally hydrophobic helices. However, for at least two of the marginally hydrophobic helices, the local interactions are not enough, indicating that post-insertional rearrangements are involved in the folding of these proteins.
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Affiliation(s)
- Linnea E Hedin
- Center for Biomembrane Research, Department of Biochemistry and Biophysics, Stockholm University, SE-106 91 Stockholm, Sweden
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45
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Protein contents in biological membranes can explain abnormal solvation of charged and polar residues. Proc Natl Acad Sci U S A 2009; 106:15684-9. [PMID: 19805218 DOI: 10.1073/pnas.0905394106] [Citation(s) in RCA: 59] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Transmembrane helices are generally believed to insert into membranes based on their hydrophobicity. Nevertheless, there are important exceptions where polar residues have great functional importance, for instance the S4 helix of voltage-gated ion channels. It has been shown experimentally that insertion can be accomplished by hydrophobic counterbalance, predicting an arginine insertion cost of only 2.5 kcal/mol, compared with 14.9 kcal/mol in cyclohexane. Previous simulations of pure bilayers have produced values close to the pure hydrocarbon, which has lead to spirited discussion about the experimental conditions. Here, we have performed computer simulations of models better mimicking biological membranes by explicitly including protein helices at mass fractions from 15% to 55%, as well as an actual translocon. This has a striking effect on the solvation free energy of arginine. With some polar residues present, the solvation cost comes close to experimental observation at approximately 30% mass fraction, and negligible at 40%. In the presence of a translocon in the membrane, the cost of inserting arginine next to the lateral gate can be as low as 3-5 kcal/mol. The effect is mainly due to the extra helices making it easier to retain hydration water. These results offer a possible explanation for the discrepancy between the in vivo hydrophobicity scale and computer simulations and highlight the importance of the high protein contents in membranes. Although many membrane proteins are stable in pure bilayers, such simplified models might not be sufficiently accurate for insertion of polar or charged residues in biological membranes.
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46
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Štrancar J, Kavalenka A, Urbančič I, Ljubetič A, Hemminga MA. SDSL-ESR-based protein structure characterization. EUROPEAN BIOPHYSICS JOURNAL: EBJ 2009; 39:499-511. [DOI: 10.1007/s00249-009-0510-5] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/15/2009] [Accepted: 06/23/2009] [Indexed: 10/20/2022]
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47
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Shi L, Cembran A, Gao J, Veglia G. Tilt and azimuthal angles of a transmembrane peptide: a comparison between molecular dynamics calculations and solid-state NMR data of sarcolipin in lipid membranes. Biophys J 2009; 96:3648-62. [PMID: 19413970 DOI: 10.1016/j.bpj.2009.02.025] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/21/2008] [Revised: 02/03/2009] [Accepted: 02/12/2009] [Indexed: 02/04/2023] Open
Abstract
We report molecular dynamics simulations in the explicit membrane environment of a small membrane-embedded protein, sarcolipin, which regulates the sarcoplasmic reticulum Ca-ATPase activity in both cardiac and skeletal muscle. In its monomeric form, we found that sarcolipin adopts a helical conformation, with a computed average tilt angle of 28 +/- 6 degrees and azymuthal angles of 66 +/- 22 degrees, in reasonable accord with angles determined experimentally (23 +/- 2 degrees and 50 +/- 4 degrees, respectively) using solid-state NMR with separated-local-field experiments. The effects of time and spatial averaging on both (15)N chemical shift anisotropy and (1)H/(15)N dipolar couplings have been analyzed using short-time averages of fast amide out-of-plane motions and following principal component dynamic trajectories. We found that it is possible to reproduce the regular oscillatory patterns observed for the anisotropic NMR parameters (i.e., PISA wheels) employing average amide vectors. This work highlights the role of molecular dynamics simulations as a tool for the analysis and interpretation of solid-state NMR data.
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Affiliation(s)
- Lei Shi
- Department of Chemistry, University of Minnesota, Minneapolis, Minnesota, USA
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48
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Kandasamy SK, Lee DK, Nanga RP, Xu J, Santos JS, Larson RG, Ramamoorthy A. Solid-state NMR and molecular dynamics simulations reveal the oligomeric ion-channels of TM2-GABAA stabilized by intermolecular hydrogen bonding. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2009; 1788:686-95. [DOI: 10.1016/j.bbamem.2008.11.009] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/05/2008] [Revised: 10/31/2008] [Accepted: 11/03/2008] [Indexed: 11/16/2022]
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49
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Johansson ACV, Lindahl E. The role of lipid composition for insertion and stabilization of amino acids in membranes. J Chem Phys 2009; 130:185101. [DOI: 10.1063/1.3129863] [Citation(s) in RCA: 58] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
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50
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Johansson ACV, Lindahl E. Titratable Amino Acid Solvation in Lipid Membranes as a Function of Protonation State. J Phys Chem B 2008; 113:245-53. [DOI: 10.1021/jp8048873] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Anna C. V. Johansson
- Center for Biomembrane Research, Department of Biochemistry and Biophysics, Stockholm University, SE-10691 Stockholm, Sweden
| | - Erik Lindahl
- Center for Biomembrane Research, Department of Biochemistry and Biophysics, Stockholm University, SE-10691 Stockholm, Sweden
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