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Voltage-gated sodium channel beta-subunits (Nav1.1-1.9) initiate and propagate action potentials in neurons and myocytes. The Nav beta-subunits (beta1-4) have been shown to modulate beta-subunit properties. Homo-oligomerization of beta-subunits on neighboring or opposing plasma membranes has been suggested to facilitate cis or trans interactions, respectively. The interactions between several Nav channel isoforms and beta-subunits have been determined using cryogenic electron microscopy (cryo-EM). Interestingly, the Nav cryo-EM structures reveal the presence of N-linked glycosylation sites. However, only the first glycan moieties are typically resolved at each site due to the flexibility of mature glycan trees. Thus, existing cryo-EM structures may risk de-emphasizing the structural implications of glycans on the Nav channels. Herein, molecular modelling and all-atom molecular dynamics simulations were applied to investigate the conformational landscape of N-linked glycans on Nav channel surfaces. The simulations revealed that negatively-charged sialic acid residues of two glycan sites may interact with voltage-sensing domains. Notably, two Nav1.5 isoform-specific glycans extensively cover the alpha-subunit region that, in other Nav channel alpha-subunit isoforms, corresponds to the binding site for the beta1- (and likely beta3-) subunit immunoglobulin (Ig) domain. Nav1.8 contains a unique N-linked glycosylation site that likely prevents its interaction with the beta2 and beta4-subunit Ig domain. These isoform-specific glycans may have evolved to facilitate specific functional interactions, for example by redirecting beta-subunit Ig-domains outwards to permit cis or trans supra-clustering within specialized cellular compartments such as the cardiomyocyte perinexal space. Further experimental work is necessary to validate these predictions.
Beaudoin et al. (Mon,) studied this question.