Steroidogenesis activator polypeptide may be a product of glucose regulated protein 78 (GRP78).
Cholesterol side-chain cleavage is sensitive to antibiotic inhibitors of protein synthesis, suggesting that a labile protein may play a regulatory role in this process. We have previously characterized such a factor--steroidogenesis activator polypeptide (SAP). Given the low molecular weight of SAP (Mr 3215), a SAP precursor has been sought. Using immunoblotting techniques with two polyclonal antisera directed against portions of the SAP sequence, a single protein of apparent Mr 82,000 (p82) can be detected in rat adrenocortical tissue. Our data suggest that adrenal p82 is most likely the widely-distributed minor heat shock protein, glucose regulated protein 78 (GRP78). The two proteins share biochemical attributes, including pI (5.2) and ATP affinity, and the reported amino acid sequences for SAP and for the carboxyl-terminal end of GRP78 are nearly identical. We propose that SAP is cleaved from GRP78--or a cognate protein--and that this proteolysis is regulated in a manner characteristic of steroidogenic tissues.
Department of Biochemistry, School of Medicine, State University of New York, Buffalo 14214.
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D000262:Adenylyl Cyclases / Q000378:metabolism; D000302:Adrenal Cortex / Q000378:metabolism*; D000818:Animals; D002352:Carrier Proteins / Q000302:isolation & purification* / Q000378:metabolism; D002460:Cell Line; D015180:Electrophoresis, Gel, Two-Dimensional; D004591:Electrophoresis, Polyacrylamide Gel; D000091342:Endoplasmic Reticulum Chaperone BiP; D006360:Heat-Shock Proteins; D015151:Immunoblotting; D007984:Leydig Cell Tumor / Q000378:metabolism*; D008297:Male; D008928:Mitochondria / Q000378:metabolism*; D018832:Molecular Chaperones; D008970:Molecular Weight; D009363:Neoplasm Proteins / Q000302:isolation & purification*; D014176:Protein Biosynthesis; D011506:Proteins / Q000302:isolation & purification*; D051381:Rats; D011916:Rats, Inbred F344
D002352:Carrier Proteins; D000091342:Endoplasmic Reticulum Chaperone BiP; C051684:GRP78 protein, rat; D006360:Heat-Shock Proteins; D018832:Molecular Chaperones; D009363:Neoplasm Proteins; D011506:Proteins; D000262:Adenylyl Cyclases