Johnson Daniel, Montpetit Marty L, Stocker Patrick J, Bennett Eric S
Department of Physiology & Biophysics and Program in Neuroscience, University of South Florida College of Medicine, Tampa, Florida 33612, USA.
J Biol Chem. 2004 Oct 22;279(43):44303-10. doi: 10.1074/jbc.M408900200. Epub 2004 Aug 16.
Voltage-gated sodium channels (Nav) are responsible for initiation and propagation of nerve, skeletal muscle, and cardiac action potentials. Nav are composed of a pore-forming alpha subunit and often one to several modulating beta subunits. Previous work showed that terminal sialic acid residues attached to alpha subunits affect channel gating. Here we show that the fully sialylated beta1 subunit induces a uniform, hyperpolarizing shift in steady state and kinetic gating of the cardiac and two neuronal alpha subunit isoforms. Under conditions of reduced sialylation, the beta1-induced gating effect was eliminated. Consistent with this, mutation of beta1 N-glycosylation sites abolished all effects of beta1 on channel gating. Data also suggest an interaction between the cis effect of alpha sialic acids and the trans effect of beta1 sialic acids on channel gating. Thus, beta1 sialic acids had no effect gating on the of the heavily glycosylated skeletal muscle alpha subunit. However, when glycosylation of the skeletal muscle alpha subunit was reduced through chimeragenesis such that alpha sialic acids did not impact gating, beta1 sialic acids caused a significant hyperpolarizing shift in channel gating. Together, the data indicate that beta1 N-linked sialic acids can modulate Nav gating through an apparent saturating electrostatic mechanism. A model is proposed in which a spectrum of differentially sialylated Nav can directly modulate channel gating, thereby impacting cardiac, skeletal muscle, and neuronal excitability.
电压门控钠通道（Nav）负责神经、骨骼肌和心脏动作电位的起始和传播。Nav由一个形成孔道的α亚基和通常一到几个调节性β亚基组成。先前的研究表明，附着在α亚基上的末端唾液酸残基会影响通道门控。在此我们表明，完全唾液酸化的β1亚基会在心脏和两种神经元α亚基同工型的稳态和动力学门控中诱导一致的超极化偏移。在唾液酸化减少的情况下，β1诱导的门控效应被消除。与此一致的是，β1 N-糖基化位点的突变消除了β1对通道门控的所有影响。数据还表明α唾液酸的顺式效应与β1唾液酸对通道门控的反式效应之间存在相互作用。因此，β1唾液酸对高度糖基化的骨骼肌α亚基的门控没有影响。然而，当通过嵌合发生使骨骼肌α亚基的糖基化减少，使得α唾液酸不影响门控时，β1唾液酸会导致通道门控出现显著的超极化偏移。总之，数据表明β1 N-连接唾液酸可通过一种明显的饱和静电机制调节Nav门控。我们提出了一个模型，其中一系列不同唾液酸化的Nav可直接调节通道门控，从而影响心脏肌肉、骨骼肌和神经元的兴奋性。
