scholarly journals Changes in Local S4 Environment Provide a Voltage-sensing Mechanism for Mammalian Hyperpolarization–activated HCN Channels

2003 ◽  
Vol 123 (1) ◽  
pp. 5-20 ◽  
Author(s):  
Damian C. Bell ◽  
Huan Yao ◽  
Renee C. Saenger ◽  
John H. Riley ◽  
Steven A. Siegelbaum
Keyword(s):  
Hcn Channels ◽  
Transmembrane Segment ◽  
Voltage Sensing ◽  
Voltage Gated ◽  
Transmembrane Segments ◽  
Pacemaker Channels ◽  
Gated Channel ◽  
Voltage Gated Channels ◽  
S4 Segment ◽  
Positively Charged

The positively charged S4 transmembrane segment of voltage-gated channels is thought to function as the voltage sensor by moving charge through the membrane electric field in response to depolarization. Here we studied S4 movements in the mammalian HCN pacemaker channels. Unlike most voltage-gated channel family members that are activated by depolarization, HCN channels are activated by hyperpolarization. We determined the reactivity of the charged sulfhydryl-modifying reagent, MTSET, with substituted cysteine (Cys) residues along the HCN1 S4 segment. Using an HCN1 channel engineered to be MTS resistant except for the chosen S4 Cys substitution, we determined the reactivity of 12 S4 residues to external or internal MTSET application in either the closed or open state of the channel. Cys substitutions in the NH2-terminal half of S4 only reacted with external MTSET; the rates of reactivity were rapid, regardless of whether the channel was open or closed. In contrast, Cys substitutions in the COOH-terminal half of S4 selectively reacted with internal MTSET when the channel was open. In the open state, the boundary between externally and internally accessible residues was remarkably narrow (∼3 residues). This suggests that S4 lies in a water-filled gating canal with a very narrow barrier between the external and internal solutions, similar to depolarization-gated channels. However, the pattern of reactivity is incompatible with either classical gating models, which postulate a large translational or rotational movement of S4 within a gating canal, or with a recent model in which S4 forms a peripheral voltage-sensing paddle (with S3b) that moves within the lipid bilayer (the KvAP model). Rather, we suggest that voltage sensing is due to a rearrangement in transmembrane segments surrounding S4, leading to a collapse of an internal gating canal upon channel closure that alters the shape of the membrane field around a relatively static S4 segment.

scholarly journals Functionality of the voltage-gated proton channel truncated in S4

2009 ◽  
Vol 107 (5) ◽  
pp. 2313-2318 ◽  
Author(s):  
Souhei Sakata ◽  
Tatsuki Kurokawa ◽  
Morten H. H. Nørholm ◽  
Masahiro Takagi ◽  
Yoshifumi Okochi ◽  
...  
Keyword(s):  
Voltage Sensor ◽  
Proton Channel ◽  
Voltage Sensing ◽  
Proton Channels ◽  
Voltage Gated ◽  
Transmembrane Segments ◽  
Cysteine Scanning ◽  
Dog Pancreas ◽  
Voltage Gated Ion Channels ◽  
Channel Properties

The voltage sensor domain (VSD) is the key module for voltage sensing in voltage-gated ion channels and voltage-sensing phosphatases. Structurally, both the VSD and the recently discovered voltage-gated proton channels (Hv channels) voltage sensor only protein (VSOP) and Hv1 contain four transmembrane segments. The fourth transmembrane segment (S4) of Hv channels contains three periodically aligned arginines (R1, R2, R3). It remains unknown where protons permeate or how voltage sensing is coupled to ion permeation in Hv channels. Here we report that Hv channels truncated just downstream of R2 in the S4 segment retain most channel properties. Two assays, site-directed cysteine-scanning using accessibility of maleimide-reagent as detected by Western blotting and insertion into dog pancreas microsomes, both showed that S4 inserts into the membrane, even if it is truncated between the R2 and R3 positions. These findings provide important clues to the molecular mechanism underlying voltage sensing and proton permeation in Hv channels.

Functional characterization of the transmembrane segment VII of the NHE1 isoform of the Na+/H+ exchangerThis paper is one of a selection of papers published in this Special Issue, entitled The Cellular and Molecular Basis of Cardiovascular Dysfunction, Dhalla 70th Birthday Tribute.

2007 ◽  
Vol 85 (3-4) ◽  
pp. 319-325 ◽  
Author(s):  
Jie Ding ◽  
Raymond W.P. Ng ◽  
Larry Fliegel
Keyword(s):  
Amino Acids ◽  
70Th Birthday ◽  
Functional Characterization ◽  
Integral Membrane Protein ◽  
Transmembrane Segment ◽  
Transmembrane Segments ◽  
Pore Lining ◽  
Positively Charged ◽  
Selection Of

The Na+/H+ exchanger isoform 1 is an integral membrane protein that regulates intracellular pH. It extrudes 1 intracellular H+ in exchange for 1 extracellular Na+. It has 2 large domains, an N-terminal membrane domain of 12 transmembrane segments and an intracellular C-terminal regulatory domain. We characterized the cysteine accessibility of amino acids of the critical transmembrane segment TM VII. Residues Leu 255, Leu 258, Glu 262, Leu 265, Asn 266, Asp 267, Val 269, Val 272, and Leu 273 were all mutated to cysteine residues in the cysteineless NHE1 isoform. Mutation of amino acids E262, N266, and D267 caused severe defects in activity and targeting of the intact full length protein. The balance of the active mutants were examined for sensitivity to the sulfhydryl reactive reagents, positively charged MTSET ((2- (trimethylammonium)ethyl)methanethiosulfonate) and negatively charged MTSES ((2-sulfonatoethyl)methanethiosulfonate). Leu 255 and Leu 258 were sensitive to MTSET but not to MTSES. The results suggest that these amino acids are pore-lining residues. We present a model of TM VII that shows that residues Leu 255, Leu 258, Glu 262, Asn 266, and Asp 267 lie near the same face of TM VII, lining the ion transduction pore.

Prediction of Ion Channels and their Types from Protein Sequences: Comprehensive Review and Comparative Assessment

2019 ◽  
Vol 20 (5) ◽  
pp. 579-592 ◽  
Author(s):  
Jianzhao Gao ◽  
Zhen Miao ◽  
Zhaopeng Zhang ◽  
Hong Wei ◽  
Lukasz Kurgan
Keyword(s):  
Ion Channels ◽  
Empirical Analysis ◽  
Protein Sequences ◽  
Voltage Gated ◽  
New Methods ◽  
Predictive Quality ◽  
Label Prediction ◽  
Gated Channel ◽  
Comprehensive Survey ◽  
Voltage Gated Channels

Background: Ion channels are a large and growing protein family. Many of them are associated with diseases, and consequently, they are targets for over 700 drugs. Discovery of new ion channels is facilitated with computational methods that predict ion channels and their types from protein sequences. However, these methods were never comprehensively compared and evaluated. </P><P> Objective: We offer first-of-its-kind comprehensive survey of the sequence-based predictors of ion channels. We describe eight predictors that include five methods that predict ion channels, their types, and four classes of the voltage-gated channels. We also develop and use a new benchmark dataset to perform comparative empirical analysis of the three currently available predictors. </P><P> Results: While several methods that rely on different designs were published, only a few of them are currently available and offer a broad scope of predictions. Support and availability after publication should be required when new methods are considered for publication. Empirical analysis shows strong performance for the prediction of ion channels and modest performance for the prediction of ion channel types and voltage-gated channel classes. We identify a substantial weakness of current methods that cannot accurately predict ion channels that are categorized into multiple classes/types. </P><P> Conclusion: Several predictors of ion channels are available to the end users. They offer practical levels of predictive quality. Methods that rely on a larger and more diverse set of predictive inputs (such as PSIONplus) are more accurate. New tools that address multi-label prediction of ion channels should be developed.

scholarly journals Coupling between Voltage Sensors and Activation Gate in Voltage-gated K+ Channels

2002 ◽  
Vol 120 (5) ◽  
pp. 663-676 ◽  
Author(s):  
Zhe Lu ◽  
Angela M. Klem ◽  
Yajamana Ramu
Keyword(s):  
Electrical Signal ◽  
K Channel ◽  
Coupling Mechanism ◽  
Excitable Cells ◽  
Voltage Sensing ◽  
K Channels ◽  
Voltage Sensors ◽  
Voltage Gated ◽  
Transmembrane Segments ◽  
Activation Gate

Current through voltage-gated K+ channels underlies the action potential encoding the electrical signal in excitable cells. The four subunits of a voltage-gated K+ channel each have six transmembrane segments (S1–S6), whereas some other K+ channels, such as eukaryotic inward rectifier K+ channels and the prokaryotic KcsA channel, have only two transmembrane segments (M1 and M2). A voltage-gated K+ channel is formed by an ion-pore module (S5–S6, equivalent to M1–M2) and the surrounding voltage-sensing modules. The S4 segments are the primary voltage sensors while the intracellular activation gate is located near the COOH-terminal end of S6, although the coupling mechanism between them remains unknown. In the present study, we found that two short, complementary sequences in voltage-gated K+ channels are essential for coupling the voltage sensors to the intracellular activation gate. One sequence is the so called S4–S5 linker distal to the voltage-sensing S4, while the other is around the COOH-terminal end of S6, a region containing the actual gate-forming residues.

scholarly journals α-Helical Structural Elements within the Voltage-Sensing Domains of a K+ Channel

1999 ◽  
Vol 115 (1) ◽  
pp. 33-50 ◽  
Author(s):  
Yingying Li-Smerin ◽  
David H. Hackos ◽  
Kenton J. Swartz
Keyword(s):  
Secondary Structure ◽  
K Channel ◽  
Structural Elements ◽  
Alanine Scanning Mutagenesis ◽  
Voltage Sensing ◽  
Tertiary Structures ◽  
Voltage Gated ◽  
Transmembrane Segments ◽  
Membrane Spanning ◽  
Pore Domain

Voltage-gated K+ channels are tetramers with each subunit containing six (S1–S6) putative membrane spanning segments. The fifth through sixth transmembrane segments (S5–S6) from each of four subunits assemble to form a central pore domain. A growing body of evidence suggests that the first four segments (S1–S4) comprise a domain-like voltage-sensing structure. While the topology of this region is reasonably well defined, the secondary and tertiary structures of these transmembrane segments are not. To explore the secondary structure of the voltage-sensing domains, we used alanine-scanning mutagenesis through the region encompassing the first four transmembrane segments in the drk1 voltage-gated K+ channel. We examined the mutation-induced perturbation in gating free energy for periodicity characteristic of α-helices. Our results are consistent with at least portions of S1, S2, S3, and S4 adopting α-helical secondary structure. In addition, both the S1–S2 and S3–S4 linkers exhibited substantial helical character. The distribution of gating perturbations for S1 and S2 suggest that these two helices interact primarily with two environments. In contrast, the distribution of perturbations for S3 and S4 were more complex, suggesting that the latter two helices make more extensive protein contacts, possibly interfacing directly with the shell of the pore domain.

scholarly journals Mechanosensitivity of ion channels based on protein–lipid interactions

2010 ◽  
Vol 7 (suppl_3) ◽  
Author(s):  
Kenjiro Yoshimura ◽  
Masahiro Sokabe
Keyword(s):  
Ion Channels ◽  
Membrane Proteins ◽  
Lipid Bilayer ◽  
Physical Environment ◽  
Energy Barrier ◽  
Mechanosensitive Channels ◽  
Transmembrane Segment ◽  
Voltage Gated ◽  
Voltage Gated Channels ◽  
Lipid Environment

Ion channels form a group of membrane proteins that pass ions through a pore beyond the energy barrier of the lipid bilayer. The structure of the transmembrane segment of membrane proteins is influenced by the charges and the hydrophobicity of the surrounding lipids and the pressure on its surface. A mechanosensitive channel is specifically designed to change its conformation in response to changes in the membrane pressure (tension). However, mechanosensitive channels are not the only group that is sensitive to the physical environment of the membrane: voltage-gated channels are also amenable to the lipid environment. In this article, we review the structure and gating mechanisms of the mechanosensitive channels and voltage-gated channels and discuss how their functions are affected by the physical properties of the lipid bilayer.

scholarly journals A novel single-domain Na+-selective voltage-gated channel in photosynthetic eukaryotes

2020 ◽  
Author(s):  
Katherine E. Helliwell ◽  
Abdul Chrachri ◽  
Julie Koester ◽  
Susan Wharam ◽  
Alison R. Taylor ◽  
...  
Keyword(s):  
Single Domain ◽  
Inactivation Kinetics ◽  
Control Mechanisms ◽  
Electrical Excitability ◽  
Voltage Gated ◽  
Photosynthetic Eukaryotes ◽  
Voltage Dependent ◽  
Gated Channel ◽  
Voltage Gated Channels ◽  
Short Time

AbstractThe evolution of Na+-selective four-domain voltage-gated channels (4D-Navs) in animals allowed rapid Na+-dependent electrical excitability, and enabled the development of sophisticated systems for rapid and long-range signalling. Whilst bacteria encode single-domain Na+-selective voltage-gated channels (BacNav), they typically exhibit much slower kinetics than 4D-Navs, and are not thought to have crossed the prokaryote-eukaryote boundary. As such, the capacity for rapid Na+-selective signalling is considered to be confined to certain animal taxa, and absent from photosynthetic eukaryotes. Certainly, in land plants, such as the Venus Flytrap where fast electrical excitability has been described, this is most likely based on fast anion channels. Here, we report a unique class of eukaryotic Na+-selective single-domain channels (EukCatBs) that are present primarily in haptophyte algae, including the ecologically important calcifying coccolithophores. The EukCatB channels exhibit very rapid voltage-dependent activation and inactivation kinetics, and sensitivity to the highly selective 4D-Nav blocker tetrodotoxin. The results demonstrate that the capacity for rapid Na+-based signalling in eukaryotes is not restricted to animals or to the presence of 4D-Navs. The EukCatB channels therefore represent an independent evolution of fast Na+-based electrical signalling in eukaryotes that likely contribute to sophisticated cellular control mechanisms operating on very short time scales in unicellular algae.One Sentence SummaryThe capacity for rapid Na+-based signalling has evolved in ecologically important coccolithophore species via a novel class of voltage-gated Na+ channels, EukCatBs.

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