Characterization of green alga, yeast, and human centrins : Specific subdomain features determine functional diversity

Centrins are a subfamily within the superfamily of Ca2+-modulated proteins that play a fundamental role in centrosome duplication and contraction of centrin-based fiber systems. We examined the individual molecular properties of yeast, green alga, and human centrins. Circular dichroism spectroscopy revealed a divergent influence of Ca2+ binding on the alpha-helical content of these proteins. Ca2+-free centrins were elongated in shape as determined by size exclusion chromatography. The presence of Ca2+ and binding peptide resulted in more spherical shaped centrins. In contrast to yeast calmodulin, centrins formed multimers in the Ca2+-bound state. This oligomerization was significantly reduced in the absence of Ca2+ and in the presence of binding peptide. The Ca2+-dependent polymerization of the green alga Scherffelia dubia centrin (SdCen) resulted in a filamentous network. This molecular property was mainly dependent on the amino-terminal subdomain and the peptide-binding site of SdCen. Finally, we analyzed whether SdCen and Cdc31p-SdCen hybrid proteins functionally substitute for the Saccharomyces cerevisiae centrin Cdc31p. Only hybrid proteins containing the amino-terminal subdomain or the third EF-hand of SdCen and the other subdomains from Cdc31p were functional in vivo.