The receptor-associated protein (RAP) binds calmodulin and is phosphorylated by calmodulin-dependent kinase II.
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.
Petersen
C M
CM
Department of Medical Biochemistry, University of Aarhus, Denmark.
Ellgaard
L
L
Nykjaer
A
A
Vilhardt
F
F
Vorum
H
H
Thøgersen
H C
HC
Nielsen
M S
MS
Jacobsen
C
C
Moestrup
S K
SK
Gliemann
J
J
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
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