1xa5
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Structure of Calmodulin in complex with KAR-2, a bis-indol alkaloid
OverviewOverview
3'-(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.
About this StructureAbout this Structure
1XA5 is a Single protein structure of sequence from Bos taurus with CA and KAR as ligands. Full crystallographic information is available from OCA.
ReferenceReference
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
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