期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：2022
卷号：119
期号：10
DOI：10.1073/pnas.2120416119
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：Significance
Ion channels have evolved the ability to communicate with one another, either through protein–protein interactions, or indirectly via intermediate diffusible messenger molecules. In special cases, the channels are part of different membranes. In muscle tissue, the T-tubule membrane is in proximity to the sarcoplasmic reticulum, allowing communication between L-type calcium channels and ryanodine receptors. This process is critical for excitation–contraction coupling and requires auxiliary proteins like junctophilin (JPH). JPHs are targets for disease-associated mutations, most notably hypertrophic cardiomyopathy mutations in the JPH2 isoform. Here we provide high-resolution snapshots of JPH, both alone and in complex with a calcium channel peptide, and show how this interaction is targeted by cardiomyopathy mutations.
Junctophilins (JPH) are a class of proteins found at junctions between the plasma membrane and the endoplasmic or sarcoplasmic reticulum, allowing for communications between proteins embedded in different membranes. JPHs have been proposed to interact with lipids as well as several ion channels, allowing for specialized communication between them. The JPH3 isoform is the target for repeats that cause Huntington’s disease-like 2, whereas JPH2 is a hot spot for mutations linked to cardiomyopathy. Here we present crystal structures of two JPH isoforms, which resemble a twisted skeleton with ribs formed by membrane occupation recognition nexus repeats, and a backbone built by a long α-helix. We captured the structure of a complex between JPH2 and a C-terminal binding site in the L-type calcium channel (Ca
V1.1) and show that this interaction is required for clustering of these channels and for robust muscle excitation–contraction coupling. Over 80 sequence variants linked to cardiomyopathy are found in different structurally important regions of JPH2, most of which affect stabilizing interactions. A subset directly affects the interaction with the L-type calcium channel. In parallel, sequence variants in the L-type calcium channel, linked to cardiac arrhythmia, also affect critical interactions.
