SONA, S.; ELLINGTON, W.R.*; Florida State Univ., Tallahssee; Florida State Univ., Tallahssee: Early Events in the Evolution of Intracellular Targeting in Creatine Kinases

Creatine kinase (CK) plays a central role in energy homeostasis in cells displaying high and variable rates of ATP turnover. A key attribute of this enzyme system is the existence of distinct isoforms that are targeted to the cytoplasm (cytCK) and mitochondrial intermembrane space (mitochondrial CK, MtCK); both isoforms are present in selected protostome and all deuterostome groups. In addition, primitive-type spermatozoa of tunicates, echinoderms and polychaetes express a unique, contiguous trimeric CK targeted to the flagellum- flagellar CK (fCK). Thus, the genes coding for cyt-, f- and MtCKs were present prior to the divergence of the two major metazoan lineages. Recently deposited cDNA sequences from the colonial hydroid Hydractinia echinata, a member of the diplobast phylum Cnidaria, reveal that this organism expresses several CKs including an MtCK and what appears to be an fCK. The MtCK has a mitochondrial targeting sequence with a well-defined proteolytic cleavage site. The other CK sequences align with the domain overlap regions of fCKs. RTPCR of total RNA from parazoan sponge Tethya aurantia produced three unique CK cDNAs. One of these CKs is clearly an MtCK as evidenced by the presence of mitochondrial targeting sequence as well as its positioning at the base of the MtCK supercluster in a phylogenetic analysis. The other two T. aurantia CKs cluster with the fCK sequences but are not contiguous trimers. Thus, we term these CKs as protoflagellar CKs. It seems likely that Mt, f- and protofCK isoforms are expressed in spermatozoa of cnidarians and sponges and possibly as well as in the choanocytes of sponges. We conclude that the CK isoform system evolved at the dawn of the radiation of multi-cellular organisms as a means of ameliorating reaction-diffusion constraints in energy transport. Supported by NSF grant IBN-0130024 to WRE.