title: The receptor-associated protein (RAP) binds calmodulin and is phosphorylated by calmodulin-dependent kinase II.
abstract: The receptor-associated protein, RAP, is an intracellular protein that may function as a chaperone for the LDL-receptor family receptors. Here we report calmodulin as the first identified RAP binding protein outside of the LDL-receptor family members. We demonstrate that RAP binds calmodulin in a Ca2+- and pH-dependent manner characteristic of calmodulin-dependent enzymes, and present evidence that RAP is a substrate for calmodulin-dependent enzymes. Thus, CaM-kinase II and calcineurin readily phosphorylate and dephosphorylate, respectively, serine residues in RAP, and in the individual RAP domains D2 (amino acids 113-218) and D3 (amino acids 219-323) which both contain sites for CaM-kinase II-mediated phosphorylation and for calmodulin binding. In addition, we provide evidence that RAP is phosphorylated by other kinases such as casein kinase II. Studies of 32[ortho]P-labelled cell cultures demonstrate that RAP is phosphorylated in vivo. Our results suggest that RAP may have hitherto unknown functions implicating phosphorylation and calmodulin-mediated modulation.
authors.affiliation: Department of Medical Biochemistry, University of Aarhus, Denmark.
authors.forename: C M
authors.initials: CM
authors.lastname: Petersen
authors.forename: L
authors.initials: L
authors.lastname: Ellgaard
authors.forename: A
authors.initials: A
authors.lastname: Nykjaer
authors.forename: F
authors.initials: F
authors.lastname: Vilhardt
authors.forename: H
authors.initials: H
authors.lastname: Vorum
authors.forename: H C
authors.initials: HC
authors.lastname: Thøgersen
authors.forename: M S
authors.initials: MS
authors.lastname: Nielsen
authors.forename: C
authors.initials: C
authors.lastname: Jacobsen
authors.forename: S K
authors.initials: SK
authors.lastname: Moestrup
authors.forename: J
authors.initials: J
authors.lastname: Gliemann
mesh_terms: D000595:Amino Acid Sequence; D019703:Calcineurin; D002118:Calcium / Q000378:metabolism; D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism*; D002147:Calmodulin / Q000378:metabolism*; D002148:Calmodulin-Binding Proteins / Q000378:metabolism; D002352:Carrier Proteins / Q000378:metabolism*; D047390:Casein Kinase II; D006023:Glycoproteins / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D026563:LDL-Receptor Related Protein-Associated Protein; D008969:Molecular Sequence Data; D010749:Phosphoprotein Phosphatases / Q000378:metabolism; D010766:Phosphorylation; D010768:Phosphoserine / Q000378:metabolism; D011499:Protein Processing, Post-Translational; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D011973:Receptors, LDL / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000378:metabolism
chemical_list: D002147:Calmodulin; D002148:Calmodulin-Binding Proteins; D002352:Carrier Proteins; D006023:Glycoproteins; D026563:LDL-Receptor Related Protein-Associated Protein; D011973:Receptors, LDL; D011993:Recombinant Fusion Proteins; D010768:Phosphoserine; D047390:Casein Kinase II; D017346:Protein Serine-Threonine Kinases; D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D019703:Calcineurin; D010749:Phosphoprotein Phosphatases; D002118:Calcium