LMA1 Binds to Vacuoles at Sec18p (NSF), Transfers upon ATP Hydrolysis to a t-SNARE (Vam3p) Complex, and Is Released during Fusion

AbstractVacuole fusion requires Sec18p (NSF), Sec17p (α-SNAP), Ypt7p (GTP binding protein), Vam3p (t-SNARE), Nyv1p (v-SNARE), and LMA1 (l ow Mr a ctivity 1, a heterodimer of thioredoxin and IB2). LMA1 requires Sec18p for saturable, high-affinity binding to vacuoles, and Sec18p “priming” ATPase requires both Sec17p and LMA1. Either the sec18-1 mutation and deletion of IB2, or deletion of both IB2 and p13 (an IB2 homolog) causes a striking synthetic vacuole fragmentation phenotype. Upon Sec18p ATP hydrolysis, LMA1 transfers to (and stabilizes) a Vam3p complex. LMA1 is released from vacuoles in a phosphatase-regulated reaction. This LMA1 cycle explains how priming by Sec18p is coupled to t-SNARE stabilization and to fusion