Activation of four enzymes by two series of calmodulin mutants with point mutations in individual Ca2+ binding sites

Zhong H. Gao, Joachim Krebs, Mark F A VanBerkum, Wei Jen Tang, John F. Maune, Anthony R. Means, James T. Stull, Kathy Beckingham

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78 Scopus citations


Activation of four target enzymes by two series of calmodulin Ca2+ binding site mutants has been examined. In each mutant, the conserved bidentate glutamate of one of the Ca2+ binding sites is mutated to glutamine or lysine. The enzymes studied were smooth and skeletal muscle myosin light chain kinases, adenylylcyclase, and plasma membrane Ca2+- ATPase. For the first three enzymes, the activation patterns with the two mutant series were very similar: mutation of site 4 was most deleterious, then site 2, site 3, and site 1. This ranking was observed previously in Ca2+ binding and Ca2+-induced conformational studies of these mutants. Thus the response of these enzymes is probably determined by the extent to which each mutant's competence to interact with target binding regions has been compromised. In contrast, for Ca2+-ATPase, mutants of sites 3 and 4 were much poorer activators than those of sites 1 and 2. Events beyond calmodulin binding and related to enzyme activation probably dictate this unusual activation pattern and also the anomalously poor activation of skeletal muscle myosin light chain kinase by site 1 mutant B1Q. Site 1 mutant B1K showed wild type activation of all four enzymes suggesting that in site 1, the lysine substitution can evoke the conformational changes associated with Ca2+ binding.

Original languageEnglish (US)
Pages (from-to)20096-20104
Number of pages9
JournalJournal of Biological Chemistry
Issue number27
StatePublished - 1993

ASJC Scopus subject areas

  • Biochemistry
  • Molecular Biology
  • Cell Biology


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