3-DIMENSIONAL STRUCTURE OF HUMAN PROTEIN-KINASE-C INTERACTING PROTEIN-1, A MEMBER OF THE HIT FAMILY OF PROTEINS

The three-dimensional structure of protein kinase C interacting protei n 1 (PKCI-1) has been solved to high resolution by x-ray crystallograp hy using single isomorphous replacement with anomalous scattering. The gene encoding human PKCI-1 was cloned from a cDNA library by using a partial sequence obtained from interactions identified in the yeast tw o-hybrid system between PKCI-1 and the regulatory domain of protein ki nase C-beta. The PKCI-1 protein was expressed in Pichia pastoris as a dimer of two 13.7-kDa polypeptides. PKCI-1 is a member of the HIT fami ly of proteins, shown by sequence identity to be conserved in a broad range of organisms including mycoplasma, plants, and humans. Despite t he ubiquity of this protein sequence in nature, no distinct function h as been shown for the protein product in vitro or in vivo. The PKCI-1 protomer has an alpha+beta meander fold containing a five-stranded ant iparallel sheet and two helices. Two protomers come together to form a 10-stranded antiparallel sheet with extensive contacts between a heli x and carboxy terminal amino acids of a protomer with the correspondin g amino acids in the other protomer. PKCI-1 has been shown to interact specifically with zinc. The three-dimensional structure has been solv ed in the presence and absence of zinc and in two crystal forms. The s tructure of human PKCI-1 provides a model of this family of proteins w hich suggests a stable fold conserved throughout nature.