Structural insights into the organization and channel behavior of Pannexin isoforms

Abstract

Pannexins are large-pore ion channels structurally related to Connexins and Innexins but remain as hemichannels to release cellular ATP upon activation. Pannexins comprise three isoforms, Pannexin1, 2, and 3, with diverse cellular roles ranging from inflammation, differentiation, and neuropathic pain to ATP release. In this study, we report the Cryo-EM structure of Pannexin3 to draw insights into the effects on channel organization and function compared to the Pannexin1 isoform. The Pannexin3 isoform displays weak ATP binding but shows similar voltage dependence compared to Pannexin1.

We also report the structures of Pannexin1 congenital mutant R217H along with a Pannexin1 double mutant W74R/R75D that mimics Pannexin2 pore residues to a resolution range of 3.8-4.2Å. The mutant structures undergo minor structural changes to form a partially closed pore. The ATP binding analysis reveals weak binding affinity of the mutants compared to wild-type Pannexin1. Moreover, the congenital mutant displays altered voltage dependence compared to the wild type. The results signify the vital role of pore-lining residues and their role in affecting pore radius in dictating pannexins' architecture and channel behavior.