CHARACTERIZATION OF GREEN-ALGA, YEAST, AND HUMAN CENTRINS - SPECIFIC SUBDOMAIN FEATURES DETERMINE FUNCTIONAL DIVERSITY

Centrins are a subfamily within the superfamily of Ca2+-modulated prot eins that play a fundamental role in centrosome duplication and contra ction of centrin-based fiber systems. We examined the individual molec ular properties of yeast, green alga, and human centrins. Circular dic hroism spectroscopy revealed a divergent influence of Ca2+ binding on the cu-helical content of these proteins. Ca2+-free centrins were elon gated in shape as determined by size exclusion chromatography. The pre sence of Ca2+ and binding peptide resulted in more spherical shaped ce ntrins. In contrast to yeast calmodulin, centrins formed multimers in the Ca2+-bound state. This oligomerization was significantly reduced i n 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-bind ing site of SdCen. Finally, we analyzed whether SdCen and Cdc31p-SdCen hybrid proteins functionally substitute for the Saccharomyces cerevis iae 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.