Pannexin1 Channels Contain a Glycosylation Site That Targets the Hexamer to the Plasma Membrane

TLDR

Pannexins are newly discovered channel proteins expressed in many tissues, especially the vertebrate CNS, and are predicted to form gap junction‑like structures based on their membrane topology and secondary structure. The study aims to determine whether N‑glycosylation of Pannexin1 regulates its trafficking to the plasma membrane. The authors used site‑directed mutagenesis of three predicted N‑linked glycosylation sites to assess their impact on Pannexin1 expression and surface targeting. Pannexin1 forms a hexameric, N‑glycosylated channel that localizes to the plasma membrane, with Asn‑254 glycosylation essential for surface targeting; glycosylation prevents intercellular docking, and electron microscopy confirms that Pannexin1 channels are dispersed rather than forming canonical gap junctions.

Abstract

Pannexins are newly discovered channel proteins expressed in many different tissues and abundantly in the vertebrate central nervous system. Based on membrane topology, folding and secondary structure prediction, pannexins are proposed to form gap junction-like structures. We show here that Pannexin1 forms a hexameric channel and reaches the cell surface but, unlike connexins, is N-glycosylated. Using site-directed mutagenesis we analyzed three putative N-linked glycosylation sites and examined the effects of each mutation on channel expression. We show for the first time that Pannexin1 is glycosylated at Asn-254 and that this residue is important for plasma membrane targeting. The glycosylation of Pannexin1 at its extracellular surface makes it unlikely that two oligomers could dock to form an intercellular channel. Ultrastructural analysis by electron microscopy confirmed that Pannexin1 junctional areas do not appear as canonical gap junctions. Rather, Pannexin1 channels are distributed throughout the plasma membrane. We propose that N-glycosylation of Pannexin1 could be a significant mechanism for regulating the trafficking of these membrane proteins to the cell surface in different tissues.