Vesicular calcium regulates coat retention, fusogenicity, and size of pre-Golgi intermediates.

The significance and extent of Ca(2+) regulation of the biosynthetic secretory pathway have been difficult to establish, and our knowledge of regulatory relationships integrating Ca(2+) with vesicle coats and function is rudimentary. Here, we investigated potential roles and mechanisms of luminal Ca(2+) in the early secretory pathway. Specific depletion of luminal Ca(2+) in living normal rat kidney cells using cyclopiazonic acid (CPA) resulted in the extreme expansion of vesicular tubular cluster (VTC) elements.

Evidence for regulation of ER/Golgi SNARE complex formation by hsc70 chaperones.

SNARE proteins control intracellular membrane fusion through formation of membrane-bridging helix bundles of amphipathic SNARE motifs. Repetitive cycles of membrane fusion likely involve repetitive folding/unfolding of the SNARE motif helical structure. Despite these conformational demands, little is known about conformational regulation of SNAREs by other proteins.

The SNARE motif contributes to rbet1 intracellular targeting and dynamics independently of SNARE interactions.

The endoplasmic reticulum/Golgi SNARE rbet1 cycles between the endoplasmic reticulum and Golgi and is essential for cargo transport in the secretory pathway. Although the quaternary SNARE complex containing rbet1 is known to function in membrane fusion, the structural role of rbet1 is unclear. Furthermore, the structural determinants for rbet1 targeting and its cyclical itinerary have not been investigated.