Structural features underlying the unusual mode of calmodulin phosphorylation by protein kinase CK2: A study with synthetic calmodulin fragments |
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Authors: | Marin O Meggio F Pinna L A |
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Institution: | Dipartimento di Chimica Biologica and Centro di Studio delle Biomembrane del C.N.R., Università di Padova, viale G. Colombo 3, Padova, 35121, Italy. |
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Abstract: | To shed light on the paradoxical behaviour of calmodulin, whose phosphorylation is inhibited by the regulatory beta-subunit of protein kinase CK2, a series of peptides encompassing the phosphoacceptor sites of calmodulin have been synthesized and assayed as substrates of CK2 alpha-subunit either alone or combined with the beta-subunit. The shortest peptide whose phosphorylation is reduced instead of being enhanced by the beta-subunit encompasses the sequence 68-106, including the central helix and the Ca2+-binding loop-III. In contrast, the phosphorylation of a peptide encompassing loop II and the central helix (54-92) is stimulated, like that of several shorter peptides, by the beta-subunit. Our data localize to the C-terminal domain of calmodulin the structural elements that are responsible for inverted susceptibility to beta-subunit regulation. |
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