Regulates protein folding in the endoplasmic reticulum (ER) lumen. Functions probably as a co-molecular chaperone that is required for normal growth of pollen tubes under high-temperature stress. Interacts with BIP1 and BIP3 (PubMed:26186593). The interaction with BIP1 and BIP3 activates the ATPase enzyme activities of BIP1 and BIP3 (PubMed:26186593). Expressed in roots, leaves, stems, flowers, mature pollen grains and growing pollen tubes. Induced by tunicamycin and heat shock (PubMed:18718935, PubMed:18980646). Induced by DTT and azetidine-2-carboxylate (PubMed:26186593). Not N-glycosylated. No visible phenotype under normal growth conditions (permissive temperature of 22 degrees Celsius), but mutant plants show gametophytic male sterility due to defect in pollen tube growth at temperature of 30 degrees Celsius.