Yeast Calmodulin: Structural and Functional Differences Compared with Vertebrate Calmodulin1

Abstract

Calmodulin of the baker's yeast (Saccharomyces cerevisiae) showed a similar affinity for Ca²⁺ to that of vertebrate calmodulin. The maximum binding number of Ca²⁺ to yeast calmodulin was, however, 3 mol/mol, which is lower than that of vertebrate calmodulin (4 mol/mol). The same maximum activity of porcine brain phospho-diesterase was attained when 100 times higher concentration of yeast calmodulin than that of vertebrate calmodulin was added. On the other hand, the maximum activation of chicken gizzard myosin light chain kinase was attained with 1,000 times higher concentration of yeast calmodulin than that of vertebrate calmodulin, and the maximum activity with yeast calmodulin was less than 1/5 of that with vertebrate calmodulin. Several amino acid substitutions observed in the yeast calmodulin, particularly at the a-helical rod connecting the two globular domains, may affect the interaction mode of various target enzymes with this calmodulin.