scholarly journals Construction and validation of a homology model of the human voltage-gated proton channel hHV1

2013 ◽  
Vol 141 (4) ◽  
pp. 445-465 ◽  
Author(s):  
Kethika Kulleperuma ◽  
Susan M.E. Smith ◽  
Deri Morgan ◽  
Boris Musset ◽  
John Holyoake ◽  
...  
Keyword(s):  
Structural Model ◽  
Proton Translocation ◽  
External Solution ◽  
Homology Model ◽  
Structural Features ◽  
Proton Channel ◽  
Dimensional Structure ◽  
Internal Solution ◽  
Voltage Gated ◽  
Homology Models

The topological similarity of voltage-gated proton channels (HV1s) to the voltage-sensing domain (VSD) of other voltage-gated ion channels raises the central question of whether HV1s have a similar structure. We present the construction and validation of a homology model of the human HV1 (hHV1). Multiple structural alignment was used to construct structural models of the open (proton-conducting) state of hHV1 by exploiting the homology of hHV1 with VSDs of K+ and Na+ channels of known three-dimensional structure. The comparative assessment of structural stability of the homology models and their VSD templates was performed using massively repeated molecular dynamics simulations in which the proteins were allowed to relax from their initial conformation in an explicit membrane mimetic. The analysis of structural deviations from the initial conformation based on up to 125 repeats of 100-ns simulations for each system reveals structural features consistently retained in the homology models and leads to a consensus structural model for hHV1 in which well-defined external and internal salt-bridge networks stabilize the open state. The structural and electrostatic properties of this open-state model are compatible with proton translocation and offer an explanation for the reversal of charge selectivity in neutral mutants of Asp112. Furthermore, these structural properties are consistent with experimental accessibility data, providing a valuable basis for further structural and functional studies of hHV1. Each Arg residue in the S4 helix of hHV1 was replaced by His to test accessibility using Zn2+ as a probe. The two outermost Arg residues in S4 were accessible to external solution, whereas the innermost one was accessible only to the internal solution. Both modeling and experimental data indicate that in the open state, Arg211, the third Arg residue in the S4 helix in hHV1, remains accessible to the internal solution and is located near the charge transfer center, Phe150.

scholarly journals Structural model of a putrescine-cadaverine permease from Trypanosoma cruzi predicts residues vital for transport and ligand binding

2013 ◽  
Vol 452 (3) ◽  
pp. 423-432 ◽  
Author(s):  
Radika Soysa ◽  
Hanka Venselaar ◽  
Jacqueline Poston ◽  
Buddy Ullman ◽  
Marie-Pierre Hasne
Keyword(s):  
Trypanosoma Cruzi ◽  
Structural Model ◽  
Three Dimensional ◽  
Salt Bridge ◽  
Homology Model ◽  
Binding Pocket ◽  
Dimensional Structure ◽  
Helical Structures ◽  
Structural Determinants ◽  
Key Residues

The TcPOT1.1 gene from Trypanosoma cruzi encodes a high affinity putrescine-cadaverine transporter belonging to the APC (amino acid/polyamine/organocation) transporter superfamily. No experimental three-dimensional structure exists for any eukaryotic member of the APC family, and thus the structural determinants critical for function of these permeases are unknown. To elucidate the key residues involved in putrescine translocation and recognition by this APC family member, a homology model of TcPOT1.1 was constructed on the basis of the atomic co-ordinates of the Escherichia coli AdiC arginine/agmatine antiporter crystal structure. The TcPOT1.1 homology model consisted of 12 transmembrane helices with the first ten helices organized in two V-shaped antiparallel domains with discontinuities in the helical structures of transmembrane spans 1 and 6. The model suggests that Trp241 and a Glu247–Arg403 salt bridge participate in a gating system and that Asn245, Tyr148 and Tyr400 contribute to the putrescine-binding pocket. To test the validity of the model, 26 site-directed mutants were created and tested for their ability to transport putrescine and to localize to the parasite cell surface. These results support the robustness of the TcPOT1.1 homology model and reveal the importance of specific aromatic residues in the TcPOT1.1 putrescine-binding pocket.

scholarly journals The first putative transmembrane helix of the 16 kDa proteolipid lines a pore in the Vo sector of the vacuolar H+-ATPase

1995 ◽  
Vol 312 (3) ◽  
pp. 739-747 ◽  
Author(s):  
P C Jones ◽  
M A Harrison ◽  
Y I Kim ◽  
M E Finbow ◽  
J B C Findlay
Keyword(s):  
Structural Model ◽  
Proton Translocation ◽  
Transmembrane Helix ◽  
Structural Features ◽  
Lipid Phase ◽  
Protein Chemistry ◽  
Alpha Helices ◽  
Multimeric Complex ◽  
Disulphide Bond Formation ◽  
Single Face

The 16 kDa proteolipid is the major component of the vacuolar H(+)-ATPase membrane sector, responsible for proton translocation. Expression of a related proteolipid from the arythropod Nephrops norvegicus in a Saccharomyces strain in which the VMA3 gene for the endogenous proteolipid has been disrupted results in restored vacuolar H(+)-ATPase function. We have used this complementation system, coupled to cysteine substitution mutagenesis and protein chemistry, to investigate structural features of the proteolipid. Consecutive cysteines were introduced individually into putative transmembrane segment 1 of the proteolipid, and at selected sites in extramembranous regions and in segment 3 and 4. Analysis of restored vacuolar H(+)-ATPase function showed that segment 1 residues sensitive to mutation to cysteine were clustered on a single face, but only if the segment was helical. Only residues insensitive to mutation could be covalently modified by the cysteine-specific reagent fluorescein 5-maleimide. A cysteine introduced into segment 3 was the only residue accessible to a relatively hydrophobic reagent, suggesting accessibility to the lipid phase. Analysis of disulphide bond formation between introduced cysteines indicates that the first transmembrane alpha-helices of each monomer are adjacent to each other at the centre of the proteolipid multimeric complex. The data are consistent with a model in which the fluorescein maleimide-accessible face of helix I lines a pore at the centre of a hexameric complex formed by the proteolipid, with the mutationally sensitive face oriented into the protein core. The implications for ion-transport function in this family of proteins are discussed in the context of this structural model.

scholarly journals Peregrination of the selectivity filter delineates the pore of the human voltage-gated proton channel hHV1

2013 ◽  
Vol 142 (6) ◽  
pp. 625-640 ◽  
Author(s):  
Deri Morgan ◽  
Boris Musset ◽  
Kethika Kulleperuma ◽  
Susan M.E. Smith ◽  
Sindhu Rajan ◽  
...  
Keyword(s):  
Transmembrane Helix ◽  
Homology Model ◽  
Selectivity Filter ◽  
Proton Channel ◽  
Suppressor Activity ◽  
Voltage Gated ◽  
Anion Permeation ◽  
Hydrogen Bond Networks ◽  
Conduction Pathway ◽  
Dynamics Simulations

Extraordinary selectivity is crucial to all proton-conducting molecules, including the human voltage-gated proton channel (hHV1), because the proton concentration is >106 times lower than that of other cations. Here we use “selectivity filter scanning” to elucidate the molecular requirements for proton-specific conduction in hHV1. Asp112, in the middle of the S1 transmembrane helix, is an essential part of the selectivity filter in wild-type (WT) channels. After neutralizing Asp112 by mutating it to Ala (D112A), we introduced Asp at each position along S1 from 108 to 118, searching for “second site suppressor” activity. Surprisingly, most mutants lacked even the anion conduction exhibited by D112A. Proton-specific conduction was restored only with Asp or Glu at position 116. The D112V/V116D channel strikingly resembled WT in selectivity, kinetics, and ΔpH-dependent gating. The S4 segment of this mutant has similar accessibility to WT in open channels, because R211H/D112V/V116D was inhibited by internally applied Zn2+. Asp at position 109 allowed anion permeation in combination with D112A but did not rescue function in the nonconducting D112V mutant, indicating that selectivity is established externally to the constriction at F150. The three positions that permitted conduction all line the pore in our homology model, clearly delineating the conduction pathway. Evidently, a carboxyl group must face the pore directly to enable conduction. Molecular dynamics simulations indicate reorganization of hydrogen bond networks in the external vestibule in D112V/V116D. At both positions where it produces proton selectivity, Asp frequently engages in salt linkage with one or more Arg residues from S4. Surprisingly, mean hydration profiles were similar in proton-selective, anion-permeable, and nonconducting constructs. That the selectivity filter functions in a new location helps to define local environmental features required to produce proton-selective conduction.

Voltage-gated proton channel is expressed on phagosome

2009 ◽  
Vol 65 ◽  
pp. S73
Author(s):  
Yoshifumi Okochi ◽  
Mari Sasaki ◽  
Yasushi Okamura
Keyword(s):  
Proton Channel ◽  
Voltage Gated

Comparison of moonlighting guanylate cyclases: roles in signal direction?

2014 ◽  
Vol 42 (6) ◽  
pp. 1773-1779 ◽  
Author(s):  
Lubna Freihat ◽  
Victor Muleya ◽  
David T. Manallack ◽  
Janet I. Wheeler ◽  
Helen R. Irving
Keyword(s):  
Interleukin 1 ◽  
Structural Features ◽  
Kinase Domain ◽  
The Novel ◽  
Natural Ligands ◽  
Signalling Cascades ◽  
A Minor ◽  
Mammalian Protein ◽  
Homology Models

Over 30 receptor-like kinases contain a guanylate cyclase (GC) catalytic centre embedded within the C-terminal region of their kinase domain in the model plant Arabidopsis. A number of the kinase GCs contain both functional kinase and GC activity in vitro and the natural ligands of these receptors stimulate increases in cGMP within isolated protoplasts. The GC activity could be described as a minor or moonlighting activity. We have also identified mammalian proteins that contain the novel GC centre embedded within kinase domains. One example is the interleukin 1 receptor-associated kinase 3 (IRAK3). We compare the GC functionality of the mammalian protein IRAK3 with the cytoplasmic domain of the plant prototype molecule, the phytosulfokine receptor 1 (PSKR1). We have developed homology models of these molecules and have undertaken in vitro experiments to compare their functionality and structural features. Recombinant IRAK3 produces cGMP at levels comparable to those produced by PSKR1, suggesting that IRAK3 contains GC activity. Our findings raise the possibility that kinase-GCs may switch between downstream kinase-mediated or cGMP-mediated signalling cascades to elicit desired outputs to particular stimuli. The challenge now lies in understanding the interaction between the GC and kinase domains and how these molecules utilize their dual functionality within cells.

Coping With Dating Violence as a Function of Violence Frequency and Solution Attribution: A Structural Modeling Approach

2012 ◽  
Vol 27 (3) ◽  
pp. 329-343 ◽  
Author(s):  
Mona Bapat ◽  
Terence J. G. Tracey
Keyword(s):  
Social Support ◽  
Physical Abuse ◽  
Dating Violence ◽  
Structural Model ◽  
External Solution ◽  
Coping Behaviors ◽  
Undergraduate Women ◽  
Level Of Use ◽  
And Coping ◽  
Positive Effect

This study presents a structural model of coping with dating violence. The model integrates abuse frequency and solution attribution to relate to college women’s choices of coping strategies. Three hundred and twenty-four undergraduate women reported being targets of some physical abuse from a boyfriend and responded to questions regarding the abuse, their solution attribution, and their coping behaviors. Solution attribution mediated the relation between frequency of the abuse and coping. Abuse frequency had a positive effect on external solution attribution, and external solution attribution had a positive effect on the level of use of active coping, utilization of social support, denial, and acceptance.

Crystal structure of the hinge domain of Smchd1 reveals its dimerization mode and nucleic acid–binding residues

2020 ◽  
Vol 13 (636) ◽  
pp. eaaz5599 ◽  
Author(s):  
Kelan Chen ◽  
Richard W. Birkinshaw ◽  
Alexandra D. Gurzau ◽  
Iromi Wanigasuriya ◽  
Ruoyun Wang ◽  
...  
Keyword(s):  
Nucleic Acid ◽  
Muscular Dystrophy ◽  
Three Dimensional ◽  
Underlying Mechanism ◽  
Structural Features ◽  
Facioscapulohumeral Muscular Dystrophy ◽  
Dimensional Structure ◽  
Nucleic Acid Binding ◽  
X Ray Crystallography ◽  
Hinge Domain

Structural maintenance of chromosomes flexible hinge domain containing 1 (SMCHD1) is an epigenetic regulator in which polymorphisms cause the human developmental disorder, Bosma arhinia micropthalmia syndrome, and the degenerative disease, facioscapulohumeral muscular dystrophy. SMCHD1 is considered a noncanonical SMC family member because its hinge domain is C-terminal, because it homodimerizes rather than heterodimerizes, and because SMCHD1 contains a GHKL-type, rather than an ABC-type ATPase domain at its N terminus. The hinge domain has been previously implicated in chromatin association; however, the underlying mechanism involved and the basis for SMCHD1 homodimerization are unclear. Here, we used x-ray crystallography to solve the three-dimensional structure of the Smchd1 hinge domain. Together with structure-guided mutagenesis, we defined structural features of the hinge domain that participated in homodimerization and nucleic acid binding, and we identified a functional hotspot required for chromatin localization in cells. This structure provides a template for interpreting the mechanism by which patient polymorphisms within the SMCHD1 hinge domain could compromise function and lead to facioscapulohumeral muscular dystrophy.

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