1.A.74 The Mitsugumin 23 (MG23) Family
Mitsugumin 23 (MG23) is a 23 kDa transmembrane protein (homologous to the Bri3 protein) localized to the sarcoplasmic/endoplasmic reticulum and nuclear membranes in a wide variety of organisms and all types (Venturi et al., 2011). Venturi et al. (2011) reported the biochemical and biophysical characterization of MG23. Hydropathicity profile and limited proteolytic analysis proposed three - five transmembrane segments and a homo-oligomeric assembly. Ultrastructural observations detected a large symmetrical particle as the predominant component and a small asymmetric assembly as the second major component in purified MG23 preparations. Single-particle three-dimensional reconstruction revealed that MG23 forms a large bowl-shaped complex equipped with a putative central pore, which may be an assembly of the small asymmetric subunit. After reconstitution into planar phospholipid bilayers, purified MG23 behaved as a voltage-dependent, cation-conducting channel, permeable to both K+ and Ca2+. Multiple channels appeared to gate together. The bowl-shaped MG23 can transiently assemble and disassemble, allowing rapid cationic flux across intracellular membrane systems.