Glycine receptor α3K governs mobility and conductance of L/K splice variant heteropentamers
Glycine receptors (GlyRs) are ligand-gated pentameric chloride channels in the central nervous system. GlyR-3 is a possible target for chronic pain treatment and temporal lobe epilepsy. Alternative splicing into K or L variants determines the subcellular fate and function of GlyR-3, yet it remains to be shown whether its different splice variants can functionally co-assemble, and what the properties of such heteropentamers would be. Here, we subjected GlyR-3 to a combined fluorescence microscopy and electrophysiology analysis. We employ masked Pearsons and dual-color spatiotemporal correlation analysis to prove that GlyR-3 splice variants heteropentamerize, adopting the mobility of the K variant. Fluorescence-based single-subunit counting experiments revealed a variable and concentration ratio dependent hetero-stoichiometry. Via single-channel on-cell patch clamp we show heteropentameric conductances resemble those of the 3K splice variant. Our data are compatible with a model where 3 heteropentamerization fine-tunes mobility and activity of GlyR 3 channels, which is important to understand and tackle 3 related diseases. SummaryThe glycine receptor 3 is key to the central nervous systems physiology and involved in chronic pain and epilepsy. In this paper, Lemmens et al. reveal and functionally characterize 3 splice variant heteropentamerization via advanced single-molecule fluorescence image analysis. DeclarationsO_ST_ABSFundingC_ST_ABSWe acknowledge the UHasselt Advanced Optical Microscopy Centre (AOMC). Prof. Em. Marcel Ameloot, the Research Foundation Flanders (FWO, project G0H3716N) and the province of Limburg (Belgium) (tUL Impuls II) are acknowledged for funding the microscopy hardware. V. Lemmens is grateful for a doctoral scholarship from the UHasselt (17DOC11BOF) and KU Leuven (C14/16/053) Special Research Funds (BOF). Conflicts of interest / competing interestsNo conflicts of interest apply. Ethics approvalNot applicable Availability of data and materialAll data and material are available upon request. Code availabilityFluctuation imaging and co-localization analyses were performed in the software package PAM [71]. The software is available as source code, requiring MATLAB to run, or as pre-compiled standalone distributions for Windows or MacOS at http://www.cup.uni-muenchen.de/pc/lamb/software/pam.html or hosted in Git repositories under http://www.gitlab.com/PAM-PIE/PAM and http://www.gitlab.com/PAM-PIE/PAMcompiled. A detailed user manual is available at http://pam.readthedocs.io. Author contributionsConceptualization Meier J.C., Brone B. and Hendrix J.; Investigation and formal analysis Lemmens V. and Thevelein B.; Software development Hendrix J.; Writing the original draft Lemmens V., Thevelein B and Hendrix, J.; Review and editing by all authors.