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Structure of Calmodulin in complex with KAR-2, a bis-indol alkaloid
Structural highlights
FunctionCALM_BOVIN Calmodulin mediates the control of a large number of enzymes, ion channels and other proteins by Ca(2+). Among the enzymes to be stimulated by the calmodulin-Ca(2+) complex are a number of protein kinases and phosphatases. Together with CEP110 and centrin, is involved in a genetic pathway that regulates the centrosome cycle and progression through cytokinesis (By similarity). Evolutionary Conservation Check, as determined by ConSurfDB. You may read the explanation of the method and the full data available from ConSurf. Publication Abstract from PubMed3'-(beta-Chloroethyl)-2',4'-dioxo-3,5'-spiro-oxazolidino-4-deacetoxyvinbla stine (KAR-2) is a potent anti-microtubular agent that arrests mitosis in cancer cells without significant toxic side effects. In this study we demonstrate that in addition to targeting microtubules, KAR-2 also binds calmodulin, thereby countering the antagonistic effects of trifluoperazine. To determine the basis of both properties of KAR-2, the three-dimensional structure of its complex with Ca(2+)-calmodulin has been characterized both in solution using NMR and when crystallized using x-ray diffraction. Heterocorrelation ((1)H-(15)N heteronuclear single quantum coherence) spectra of (15)N-labeled calmodulin indicate a global conformation change (closure) of the protein upon its binding to KAR-2. The crystal structure at 2.12-A resolution reveals a more complete picture; KAR-2 binds to a novel structure created by amino acid residues of both the N- and C-terminal domains of calmodulin. Although first detected by x-ray diffraction of the crystallized ternary complex, this conformational change is consistent with its solution structure as characterized by NMR spectroscopy. It is noteworthy that a similar tertiary complex forms when calmodulin binds KAR-2 as when it binds trifluoperazine, even though the two ligands contact (for the most part) different amino acid residues. These observations explain the specificity of KAR-2 as an anti-microtubular agent; the drug interacts with a novel drug binding domain on calmodulin. Consequently, KAR-2 does not prevent calmodulin from binding most of its physiological targets. The structure of the complex of calmodulin with KAR-2: a novel mode of binding explains the unique pharmacology of the drug.,Horvath I, Harmat V, Perczel A, Palfi V, Nyitray L, Nagy A, Hlavanda E, Naray-Szabo G, Ovadi J J Biol Chem. 2005 Mar 4;280(9):8266-74. Epub 2004 Dec 13. PMID:15596444[1] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. See AlsoReferences
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