1.A.25.2.3
Pannexin-3, PANX3, of 392 aas and 5 TMSs, is reported to form functional, single membrane, cell surface channels (Penuela et al., 2007)). It functions as an ER Ca²⁺ channel, hemichannel, and gap junction to promote osteoblast differentiation (Ishikawa et al., 2011). However, Panx3 expression in osteoblasts is not required for postnatal bone remodeling (Yorgan et al. 2019).  PANX3 contributes to various developmental and pathophysiological processes by permeating ATP and Ca²⁺ ions.  The cryo-EM structure of human PANX3 has been solved at 2.9-3.2 Å (Tsuyama et al. 2025). The PANX3 channel is heptameric and forms a transmembrane pore along the central symmetric axis. The narrowest constriction of the pore is composed of an isoleucine ring located in the extracellular region, and its size is comparable to that of other pannexins.