Crystal structure and molecular imaging of the Nav channel ?3 subunit indicates a trimeric assembly.

ABSTRACT: The vertebrate sodium (Nav) channel is composed of an ion-conducting ? subunit and associated ? subunits. Here, we report the crystal structure of the human ?3 subunit immunoglobulin (Ig) domain, a functionally important component of Nav channels in neurons and cardiomyocytes. Surprisingly, we found that the ?3 subunit Ig domain assembles as a trimer in the crystal asymmetric unit. Analytical ultracentrifugation confirmed the presence of Ig domain monomers, dimers, and trimers in free solution, and atomic force microscopy imaging also detected full-length ?3 subunit monomers, dimers, and trimers. Mutation of a cysteine residue critical for maintaining the trimer interface destabilized both dimers and trimers. Using fluorescence photoactivated localization microscopy, we detected full-length ?3 subunit trimers on the plasma membrane of transfected HEK293 cells. We further show that ?3 subunits can bind to more than one site on the Nav 1.5 ? subunit and induce the formation of ? subunit oligomers, including trimers. Our results suggest a new and unexpected role for the ?3 subunits in Nav channel cross-linking and provide new structural insights into some pathological Nav channel mutations.

SUBMITTER: Namadurai S 

PROVIDER: S-EPMC4036194 | biostudies-literature | 2014 Apr

REPOSITORIES: biostudies-literature