Hv1: How A Voltage-sensor May Form A

ChannelYounes Mokrab

Biophysical Society 53rd Annual Meeting

2 Mar 2009

Hv1: a VS with proton channel activity

Ramsey et al. 2006Schilling et al. 2002

H+

S1 S2 S3 S4

+++

• Exact function not known but enriched in immune tissue.

• Topology similar to VS domains of voltage-gated ion channels.

• In response to depolarising potential, it conducts an outward H+ current, with similar characteristics to GvH+.

• Conduction pore and molecular mechanism is still unknown

Istep

-Itail

Homology open-state models for Hv1 and simulation of insertion

into bilayer

Bond et al. 2006, Jiang et al. 2002, Jiang et al. 2003, Long et al. 2007

4:1

Full-atom Coarse-grain

Protein

Lipid

Water

Ion

Hv1 homology models based on x-ray structures of KvAP, Kv1.2 and Kv1.2-2.1 chimera.

Self assembly in POPC for 320 ns

Protein inserted to membrane

Coarse-grain (CG) models

Full-atom simulations based on CG configuration of protein in bilayer

Per-residue fluctuationBackbone RMSD versus time

Conversion of system to full-atom using LSF

Full-atom simulation for 20 ns

Hydrophilic residues cluster along the centre of the Hv1 bundle

Chimera-based Kv1.2-based kvAP-based

• Models might capture different open-state conformations, all showing charged/polar residues which line a potential conduction pathway for H+ during Hv1 activation.

A water-permeable pore forms along central axis of Hv1

• Analysis of water density during simulation shows water penetration of Hv1 along its central axis in the models, forming a potential water permeable pore.

Chimera-based Kv1.2-based kvAP-based

Water molecules are coordinated by polar and charged residues

• A number of charged side chains are identified which may be involved in direct H+ translocation, and/or polar side chains in general might coordinate a ‘proton wire’.

• In silico and In vivo mutagenesis experiment in progress to test the roles of specific residues.

Water pore absent from VS homologues

Chimera Kv1.2 kvAP

• Simulations of other voltage-gated channels show considerably-reduced water penetration along the central axis of the VS domains.

Pore-lining residues unique to Hv1

Conclusions and future directions

• Combined CG-AT simulations of Hv1 open-state models in solvated lipid bilayer reveals a central water-permeable pore which seems to be absent from other VS proteins.

• High water density sites in a potential ‘gating pore’ in Hv1 appear to be coordinated by uniquely conserved polar and charged residues.

• Role of specific residues in water coordination is being tested by in silico and in vivo site-directed mutagenesis.

Acknowledgments

• Professor Mark Sansom, SBCB, University of Oxford.

• Dr Scott Ramsey and Professor David Clapham, Harvard Medical School (Poster 3415-Pos B462, Wed 4 Mar 1-3 pm).

• Dr Zara Sands, AstraZeneca, Sweden.

• Dr Kathryn Scott, Dr Phil Stansfeld, Dr Kaihsu Tai and members of SBCB.