Molecular Modeling and Dynamics of a Complete Connexin-43 Gap Junction Channel in Various Phosphorylation States.

Gap junction channels, formed by the docking of two hemichannels from adjacent cells, are essential for intercellular communication. Connexin-43 (Cx43), the most widely expressed connexin, is critically involved in numerous physiological processes. Phosphorylation of Cx43 is a key regulatory mechanism that influences all aspects of its function, including trafficking, channel gating, and permeability. Here, we report a full-length computational model of the dodecameric Cx43 gap junction channel in double bilayers, including its intracellular loops and cytoplasmic regulatory C-terminal domains (CTDs). Furthermore, we performed all-atom molecular dynamics simulations of four systems representing different phosphorylation states. Our results demonstrate that increased phosphorylation of serine residues in the CTD induces more extended and flexible CTD conformations with greater solvent exposure, meanwhile narrowing the channel pore. Distinct gating states are closely associated with hydrophobic interactions between the N-terminal helices (NTHs) and transmembrane domain 2 (TM2). Unfolding of the NTHs disrupts the interactions, leading to pore distortion and a transition from the initial closed state to a more open conformation. These findings provide novel insights into the structural dynamics and regulatory mechanisms of the Cx43 gap junction channels.