Frog p26olf is a novel S100-like Ca21-binding protein found in olfactory cilia. It consists of two S100-like domains aligned sequentially, and has a total of four Ca21-binding sites (known as EF-hands). In this study, to elucidate the mechanism of Ca21-binding to each EF-hand (named EF-A, -B, -C and -D from the N-terminus of p26olf), we examined Ca21-binding in wild-type p26olf and also in its mutants in which a glutamate at the –z coordinate position within each Ca21-binding loop was substituted for a glutamine. Flow dialysis experiments showed that the wild-type binds nearly four Ca21 per molecule maximally, while all the.
