Onchocerca volvulus Calcium Binding Protein (EF12)

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A 542 residue protein of unknown function has been isolated from the nematode, Onchocerca volvulus, as well as its close homolog of 482 residues from Caenorhabditis elegans [50]. It has twelve EF-hands, eleven of which conform well to the consensus of figure 1 and appear to bind calcium. The fourth EF-hand is highly diverged; however, of all EF-hand domains it most closely resembles EF12 #2. The eleven interdomain spacings are all six residues; this pattern strengthens the interpretation that the 41 (6 + 29 + 6) residues between EF-hands 3 and 5 harbors an aberrant domain. In a dendrogram the six ODD domains cluster together and are congruent with the six EVEN domains. Further domains 1(2) & 7(8), 3(4) & 9(10), and 5(6) & 11(12) most closely resemble one another, reflecting four cycles of gene duplication and fusion. It is surely significant that the O. volvulus and the C. elegans proteins align well, with no deletions, over the 414 residues (12 * 29 + 11 * 6) residues encompassing the twelve EF- hands but show many deletions in the N-terminal and C-terminal domains. The six pairs of EF-hands might be arranged helically and undergo a cooperative change in conformation upon binding calcium.