C terminal block of the Pannexin 1 channel pore and its relief by proteolytic cleavage

Abstract

Pannexin‐1 (PANX1) channels release ATP, a “find‐me” signal that recruits macrophages to apoptosing cells. Cleavage of the PANX1 C terminus by caspases represents a new mechanism of ion channel opening, but how the C terminus regulates channel activity is unclear. We provide evidence suggesting that the C terminal residues of PANX1 block the pore and removing this block activates the channel. Silent channels could be activated directly by C terminal cleavage, in the absence of additional apoptotic factors. We identified a region immediately downstream of the caspase site required for inhibition of PANX1. Consistent with the C terminus acting as a pore blocker, we found that constitutively active channels could be inhibited, in trans, by the isolated C terminus. Furthermore, using a cysteine crosslinking approach, we show that relief of inhibition following cleavage requires dissociation of the C terminus from the channel pore. Together, these data suggest a ball & chain mechanism of PANX1 activation, wherein the C terminus blocks the full length channel and a remarkably well placed caspase cleavage site allows effective removal of inhibitory C terminal residues to facilitate channel opening.