Allosteric modulation of LRRC8 channels by targeting their cytoplasmic domains

Volume-regulated anion channels (VRACs) are heteromers of LRRC8 proteins, all containing the obligatory subunit LRRC8A. Here, the authors develop and characterize nanobodies that bind LRRC8A and allosterically modulate the function of homomeric LRRC8A and endogenous heteromeric channels, hinting at functional mechanisms present in VRACs. Members of the LRRC8 family form heteromeric assemblies, which function as volume-regulated anion channels. These modular proteins consist of a transmembrane pore and cytoplasmic leucine-rich repeat (LRR) domains. Despite their known molecular architecture, the mechanism of activation and the role of the LRR domains in this process has remained elusive. Here we address this question by generating synthetic nanobodies, termed sybodies, which target the LRR domain of the obligatory subunit LRRC8A. We use these binders to investigate their interaction with homomeric LRRC8A channels by cryo-electron microscopy and the consequent effect on channel activation by electrophysiology. The five identified sybodies either inhibit or enhance activity by binding to distinct epitopes of the LRR domain, thereby altering channel conformations. In combination, our work provides a set of specific modulators of LRRC8 proteins and reveals the role of their cytoplasmic domains as regulators of channel activity by allosteric mechanisms.

Automated summary

In this study, nanobodies targeting the LRR domain of LRRC8A have been developed and characterized, providing specific modulators for LRRC8 proteins and revealing the role of their cytoplasmic domains in regulating channel activity through allosteric mechanisms. Cryo-electron microscopy and electrophysiology experiments showed that these nanobodies can alter LRRC8A channel activity by binding to distinct epitopes of the LRR domain and changing channel conformations.