May regulate calcium-dependent activities in the endoplasmic reticulum lumen or post-ER compartment. Isoform 5 may be involved in the exocytosis of zymogens by pancreatic acini. Isoform 5 interacts with STXBP1; the interaction is enhanced in presence of calcium. Isoform 5 interacts with STX3. Isoform 5 colocalizes with STX3 and STXBP1 isoform 2 at the plasma membrane and cell surface blebs. Ubiquitous. Isoform 5 is expressed in pancreas. Binds calcium via its EF-hands (By similarity). Isoform 5 binds calcium. Belongs to the CREC family.