Target Recognition of Apocalmodulin by Nitric Oxide Synthase I Peptides

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• 作者：Petra Censarek ; Michael Beyermann ; and Karl-Wilhelm Koch
• 刊名：Biochemistry
• 出版年：2002
• 出版时间：July 9, 2002
• 年：2002
• 卷：41
• 期：27
• 页码：8598 - 8604
• 全文大小：228K
• 年卷期：v.41,no.27(July 9, 2002)
• ISSN：1520-4995

文摘

An increasing number of proteins are found that are regulated by the Ca²⁺-free state ofcalmodulin, apocalmodulin. Many of these targets harbor a so-called IQ motif within their primary sequence,but several target proteins of apocalmodulin lack this motif. We investigated whether the Ca²⁺-dependentcalmodulin-binding site of nitric oxide synthase I could be transformed into a target site of apocalmodulin.Synthetic peptides representing the wild-type amino acid sequence and several peptides carrying mutationswere studied by isothermal titration calorimetry and fluorescence spectroscopy. A single amino acidsubstitution of a negative charge to a positive charge can convert a classical Ca²⁺-dependent binding siteof calmodulin into a target site for apocalmodulin. In addition, the introduction of hydrophobic aminoacids increases the apparent binding affinity from the micromolar to the nanomolar range. Binding ofwild-type and mutant peptides to Ca²⁺-calmodulin was enthalpically driven, and binding to apocalmodulinwas entropically driven. Our data indicate that only a few selected amino acid positions in a calmodulin-binding site determine its Ca²⁺ dependency.