Secondary structure of a calcium binding protein (CaBP) from Entamoeba histolytica

Abstract

A calcium binding protein from Entamoeba histolytica, (EhCaBP, M_r~15 kDa) is the causative agent for amoebiosis and has a very low sequence homology (~30%) with other known CaBPs. Almost complete sequence specific resonance assignments for ¹H, ¹³C and ¹⁵N spins in EhCaBP were obtained using double and triple resonance NMR experiments. Qualitative interpretation of the nuclear Overhauser enhancements, chemical shift indices and of hydrogen exchange rates threw valuable light upon the secondary structure of this protein. CaBP is found to have two globular domains each of which consists of two pairs of helix-loop-helix motifs. Though this protein has a very small sequence homology with calmodulins, the topological arrangement of the α-helices and β-strands in EhCaBP resemble them.