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Biophysical Journal
Article . 2015 . Peer-reviewed
License: Elsevier Non-Commercial
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Molecular Basis of the Membrane Interaction of the β2e Subunit of Voltage-Gated Ca2+ Channels

Authors: Kim, Dong-Il; Kang, Mooseok; Kim, Sangyeol; Lee, Juhwan; Park, Yongsoo; Chang, Iksoo; Suh, Byung-Chang;

Molecular Basis of the Membrane Interaction of the β2e Subunit of Voltage-Gated Ca2+ Channels

Abstract

The auxiliary β subunit plays an important role in the regulation of voltage-gated calcium (CaV) channels. Recently, it was revealed that β2e associates with the plasma membrane through an electrostatic interaction between N-terminal basic residues and anionic phospholipids. However, a molecular-level understanding of β-subunit membrane recruitment in structural detail has remained elusive. In this study, using a combination of site-directed mutagenesis, liposome-binding assays, and multiscale molecular-dynamics (MD) simulation, we developed a physical model of how the β2e subunit is recruited electrostatically to the plasma membrane. In a fluorescence resonance energy transfer assay with liposomes, binding of the N-terminal peptide (23 residues) to liposome was significantly increased in the presence of phosphatidylserine (PS) and phosphatidylinositol 4,5-bisphosphate (PIP2). A mutagenesis analysis suggested that two basic residues proximal to Met-1, Lys-2 (K2) and Trp-5 (W5), are more important for membrane binding of the β2e subunit than distal residues from the N-terminus. Our MD simulations revealed that a stretched binding mode of the N-terminus to PS is required for stable membrane attachment through polar and nonpolar interactions. This mode obtained from MD simulations is consistent with experimental results showing that K2A, W5A, and K2A/W5A mutants failed to be targeted to the plasma membrane. We also investigated the effects of a mutated β2e subunit on inactivation kinetics and regulation of CaV channels by PIP2. In experiments with voltage-sensing phosphatase (VSP), a double mutation in the N-terminus of β2e (K2A/W5A) increased the PIP2 sensitivity of CaV2.2 and CaV1.3 channels by ∼3-fold compared with wild-type β2e subunit. Together, our results suggest that membrane targeting of the β2e subunit is initiated from the nonspecific electrostatic insertion of N-terminal K2 and W5 residues into the membrane. The PS-β2e interaction observed here provides a molecular insight into general principles for protein binding to the plasma membrane, as well as the regulatory roles of phospholipids in transporters and ion channels.

Keywords

Phosphatidylinositol 4,5-Diphosphate, CALCIUM-CHANNELS, 570, PHOSPHATIDYLINOSITOL 4,5-BISPHOSPHATE, DYNAMIC PALMITOYLATION, Calcium Channels, L-Type, Protein Conformation, Molecular Sequence Data, BETA(2A) SUBUNIT, Intracellular Space, 610, ACIDIC LIPIDS, Molecular Dynamics Simulation, PLASMA-MemBRANE, Mice, Calcium Channels, N-Type, Animals, Humans, Amino Acid Sequence, COMPUTER-SIMULATIONS, LIPID-BILAYERS, Cell Membrane, Proteins, Binding, Electrophysiological Phenomena, Rats, Protein Transport, Liposomes, Mutation, Mutagenesis, Site-Directed, Hydrophobic and Hydrophilic Interactions, Protein Binding

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citations
This is an alternative to the "Influence" indicator, which also reflects the overall/total impact of an article in the research community at large, based on the underlying citation network (diachronically).
BIP!Citations provided by BIP!
popularity
This indicator reflects the "current" impact/attention (the "hype") of an article in the research community at large, based on the underlying citation network.
BIP!Popularity provided by BIP!
influence
This indicator reflects the overall/total impact of an article in the research community at large, based on the underlying citation network (diachronically).
BIP!Influence provided by BIP!
impulse
This indicator reflects the initial momentum of an article directly after its publication, based on the underlying citation network.
BIP!Impulse provided by BIP!
21
Top 10%
Average
Top 10%
Green
hybrid