TRAP proteins are part of a complex whose function is to bind calcium to the ER membrane and thereby regulate the retention of ER resident proteins. May be involved in the recycling of the translocation apparatus after completion of the translocation process or may function as a membrane-bound chaperone facilitating folding of translocated proteins. Heterotetramer of TRAP-alpha, TRAP-beta, TRAP-delta and TRAP-gamma. Interacts with palmitoylated calnexin (CALX), the interaction is required for efficient folding of glycosylated proteins. Shows a remarkable charge distribution with the N-terminus being highly negatively charged, and the cytoplasmic C-terminus positively charged. Seems to bind calcium. Belongs to the TRAP-alpha family.