1XA5

Structure of Calmodulin in complex with KAR-2, a bis-indol alkaloid

Summary for 1XA5

• Entry DOI: 10.2210/pdb1xa5/pdb
• Descriptor: Calmodulin, CALCIUM ION, 3"-(BETA-CHLOROETHYL)-2",4"-DIOXO-3, 5"-SPIRO-OXAZOLIDINO-4-DEACETOXY-VINBLASTINE, ... (4 entities in total)
• Functional Keywords: calmodulin, vinca alkaloid, kar-2, drug binding, metal binding protein
• Biological source: Bos taurus (cattle)
• Total number of polymer chains: 1
• Total formula weight: 17708.08

Authors

Horvath, I.,Harmat, V.,Hlavanda, E.,Naray-Szabo, G.,Ovadi, J. (deposition date: 2004-08-25, release date: 2004-12-21, Last modification date: 2023-10-25)

Primary citation

Horvath, I.,Harmat, V.,Perczel, A.,Palfi, V.,Nyitrai, L.,Nagy, A.,Hlavanda, E.,Naray-Szabo, G.,Ovadi, J.
The structure of the complex of calmodulin with KAR-2: a novel mode of binding explains the unique pharmacology of the drug
J.Biol.Chem., 280:8266-8274, 2005

PubMed Abstract: 3'-(beta-Chloroethyl)-2',4'-dioxo-3,5'-spiro-oxazolidino-4-deacetoxyvinblastine (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.

PubMed: 15596444
DOI: 10.1074/jbc.M410353200

Experimental method

X-RAY DIFFRACTION (2.12 Å)