Phosphorylation of the IQ domain regulates the interaction between Ca2+-vector protein and its target in Amphioxus.
Calcium vector protein target (CaVPT), a 26-kDa endogenous target of calcium vector protein from Amphioxus (CaVP), contains three distinct regions: a N-terminal Pro-Ala-Lys-rich motif, segment 36-50 displaying sequence similarity to the calmodulin-binding site in neuromodulin and neurogranin where they are designated as the IQ domain; and two immunoglobulin-like folds. The phosphorylation by protein kinase C of Ser-43 in the IQ domain drastically decreases the affinity of CaVPT for CaVP and CaVP protects CaVPT from phosphorylation. Phosphorylation by the catalytic subunit of cyclic AMP-dependent protein kinase has a similar effect, but in addition to Ser-43 four other phosphorylated sites were identified. Removal of the Pro-Ala-Lys-rich region and the IQ domain in CaVPT by trypsin leads to the loss of binding to CaVP, whereas the chymotryptic fragment, containing these regions and first immunoglobulin-like domain, retained the ability to interact with CaVP. A synthetic IQ domain alone interacts strongly with calmodulin, but not with CaVP. Two main conclusions can be drawn from this study: 1) the regulation of interaction between CaVP and CaVPT is very similar to the mechanism observed in the complex between neuromodulin or neurogranin and calmodulin; 2) in spite of this similarity the entire CaVP-binding site is not restricted to the IQ domain; in addition the Pro-Ala-Lys-rich motif may be necessary for high affinity binding to CaVP.
Department of Biochemistry, University of Geneva, CH-1211 Geneva 4, Switzerland.
T V
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Petrova
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Takagi
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Cox
D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D002135:Calcium-Binding Proteins / Q000378:metabolism*; D002147:Calmodulin / Q000378:metabolism; D002384:Catalysis; D002417:Cattle; D002816:Chordata, Nonvertebrate / Q000378:metabolism*; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism; D006868:Hydrolysis; D008969:Molecular Sequence Data; D009124:Muscle Proteins / Q000378:metabolism*; D010446:Peptide Fragments / Q000378:metabolism*; D010766:Phosphorylation; D051381:Rats; D016415:Sequence Alignment; D013552:Swine
C050084:CAVP protein, Amphioxus; D002135:Calcium-Binding Proteins; D002147:Calmodulin; D009124:Muscle Proteins; D010446:Peptide Fragments; D017868:Cyclic AMP-Dependent Protein Kinases