Identification of high-affinity calmodulin-binding proteins in rat liver.
The Ca2+-dependent binding of [125I]calmodulin (CaM) to hepatic proteins separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) was utilized to identify CaM binding or "acceptor" proteins or CAPs. Two proteins of apparent molecular weight of 60,000 (CAP-60) and 45,000 (CAP-45) comprised greater than 80% of the Ca2+-dependent CaM binding in rat liver cytosol. CAP-60 and CAP-45 were partially purified by a variety of chromatographic steps, including affinity chromatography on CaM Sepharose. CAP-60 possessed a native molecular size of 400,000, indicating it to be the CaM-binding "subunit" of a larger oligomeric complex. In contrast, CAP-45 was monomeric as judged by gel filtration. Neither CAP-60 nor CAP-45 possessed chromatographic properties consistent with known CaM-dependent enzymes reported in the literature. Two-dimensional peptide mapping provided convincing evidence that CAP-60 and CAP-45 were unrelated to other well-characterized CAPs, namely Ca2+ (CaM)-dependent protein kinase II, calcineurin, or the CaM-dependent cyclic nucleotide phosphodiesterase. The relative abundance and high affinity for CaM could suggest that these novel target proteins, CAP-60 and CAP-45, represent a dominant pathway for CaM action in the mammalian liver.
Hanley
R M
RM
Dedman
J R
JR
Shenolikar
S
S
D000818:Animals; D002118:Calcium / Q000378:metabolism; D002147:Calmodulin / Q000378:metabolism*; D002148:Calmodulin-Binding Proteins / Q000378:metabolism*; D047388:Casein Kinases; D003600:Cytosol / Q000032:analysis; D008099:Liver / Q000378:metabolism*; D008970:Molecular Weight; D010446:Peptide Fragments / Q000032:analysis; D011493:Protein Kinase C / Q000378:metabolism; D011494:Protein Kinases / Q000378:metabolism; D051381:Rats
D002147:Calmodulin; D002148:Calmodulin-Binding Proteins; D010446:Peptide Fragments; D011494:Protein Kinases; D047388:Casein Kinases; D011493:Protein Kinase C; D002118:Calcium