BAP, a mammalian BiP-associated protein, is a nucleotide exchange factor that regulates the ATPase activity of BiP.
We identified a mammalian BiP-associated protein, BAP, using a yeast two-hybrid screen that shared low homology with yeast Sls1p/Sil1p and mammalian HspBP1, both of which regulate the ATPase activity of their Hsp70 partner. BAP encoded an approximately 54-kDa protein with an N-terminal endoplasmic reticulum (ER) targeting sequence, two sites of N-linked glycosylation, and a C-terminal ER retention sequence. Immunofluorescence staining demonstrated that BAP co-localized with GRP94 in the endoplasmic reticulum. BAP was ubiquitously expressed but showed the highest levels of expression in secretory organ tissues, a pattern similar to that observed with BiP. BAP binding was affected by the conformation of the ATPase domain of BiP based on in vivo binding studies with BiP mutants. BAP stimulated the ATPase activity of BiP when added alone or together with the ER DnaJ protein, ERdj4, by promoting the release of ADP from BiP. Together, these data demonstrate that BAP serves as a nucleotide exchange factor for BiP and provide insights into the mechanisms that control protein folding in the mammalian ER.
D000251:Adenosine Triphosphatases / Q000378:metabolism; D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D015152:Blotting, Northern; D019556:COS Cells; D002352:Carrier Proteins / Q000737:chemistry* / Q000378:metabolism / Q000502:physiology*; D002460:Cell Line; D003001:Cloning, Molecular; D018076:DNA, Complementary / Q000378:metabolism; D000091342:Endoplasmic Reticulum Chaperone BiP; D005822:Genetic Vectors; D006023:Glycoproteins / Q000378:metabolism; D006026:Glycoside Hydrolases / Q000494:pharmacology; D020662:Guanine Nucleotide Exchange Factors; D006360:Heat-Shock Proteins; D006801:Humans; D018832:Molecular Chaperones / Q000737:chemistry* / Q000378:metabolism; D008969:Molecular Sequence Data; D011485:Protein Binding; D011487:Protein Conformation; D011994:Recombinant Proteins / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D013997:Time Factors; D014018:Tissue Distribution; D014162:Transfection; D014415:Tunicamycin / Q000494:pharmacology; D020798:Two-Hybrid System Techniques
D002352:Carrier Proteins; D018076:DNA, Complementary; D000091342:Endoplasmic Reticulum Chaperone BiP; D006023:Glycoproteins; D020662:Guanine Nucleotide Exchange Factors; D006360:Heat-Shock Proteins; D018832:Molecular Chaperones; D011994:Recombinant Proteins; C418483:SIL1 protein, human; D014415:Tunicamycin; D006026:Glycoside Hydrolases; D000251:Adenosine Triphosphatases