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Structure. 2003 Jan;11(1):75-85.

Metal-free and Ca2+-bound structures of a multidomain EF-hand protein, CBP40, from the lower eukaryote Physarum polycephalum.

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Department of Applied Biological Chemistry, Graduate School of Agricultural and Life Sciences, University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-8657, Japan.


Acellular slime mold, Physarum polycephalum, has a unique wound-healing system. When cytoplasm of plasmodia is exposed to extracellular fluid, calcium binding protein 40 (CBP40) seals damaged areas, forming large aggregates Ca(2+) dependently. Part of the CBP40 is truncated at the N terminus by a proteinase in plasmodia (CBP40delta), which does not aggregate in the Ca(2+)-bound form. Here we report the crystal structures of CBP40delta in both the metal-free and the Ca(2+)-bound states. Both structures consist of three domains: coiled-coil, intervening, and EF-hand. The topology of the EF-hand domain is similar to that of calpain. The N-terminal half of CBP40Delta interacts with the C-terminal EF-hands through a large hydrophobic interface, necessary for high Ca(2+) affinity. Conformational change upon Ca(2+) binding is small; however, the structure of CBP40delta provides novel insights into the mechanism of Ca(2+)-dependent oligomerization.

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