HSPA5/GRP-78 Protein, Mouse (P.pastoris, His)

HSPA5/GRP-78 Protein serves as a crucial endoplasmic reticulum chaperone, playing a pivotal role in protein folding and quality control within the endoplasmic reticulum lumen. It engages in correct protein folding and participates in the degradation of misfolded proteins, collaborating with DNAJC10/ERdj5 to facilitate the release of DNAJC10/ERdj5 from its substrate. Furthermore, HSPA5/GRP-78 acts as a key repressor of the ERN1/IRE1-mediated unfolded protein response (UPR). In the unstressed endoplasmic reticulum, it is recruited by DNAJB9/ERdj4 to the luminal region of ERN1/IRE1, disrupting the dimerization of ERN1/IRE1 and consequently inactivating it. The accumulation of misfolded proteins triggers the release of HSPA5/BiP from ERN1/IRE1, allowing for homodimerization and the subsequent activation of ERN1/IRE1. Additionally, HSPA5/GRP-78 plays an auxiliary role in the post-translational transport of small presecretory proteins across the endoplasmic reticulum and may function as an allosteric modulator for the SEC61 channel-forming translocon complex. It is suggested to cooperate with SEC62 to enable the productive insertion of these precursors into the SEC61 channel. The protein appears to specifically regulate the translocation of precursors with inhibitory residues in their mature region, which weaken channel gating. Beyond its role in protein folding, HSPA5/GRP-78 may also contribute to apoptosis and cell proliferation.