Early evolution of metazoan serine/threonine and tyrosine kinases: identification of selected kinases in marine sponges

The phylum Porifera (sponges) was the first to diverge from the commonancestor of the Metazoa. In this study, six cDNAs coding for protein-serine/threonine kinases (PS/TKs) are presented; they have been isolatedfrom libraries obtained from the demosponges Geodia cydonium and Suberitesdomuncula and from the calcareous sponge Sycon raphanus. Sequencealignments of the catalytic domains revealed that two major families ofPS/TK, the "conventional" (Ca(2+)-dependent) protein kinase C (PKC), thecPKC subfamily, as well as the "novel" (Ca(2+)- independent) PKC (nPKC),form two separate clusters. In each cluster, the sequence from S. raphanusdiverges first. To approach the question about the origin ofprotein-tyrosine kinases (PTK), which are found only in Metazoa, weanalyzed two additional PS/TKs which have been cloned from S. domuncula:the stress-responsive protein kinase (KRSvSD) and theprotein-kinase-C-related kinase (PRKvSD). The construction of thephylogenetic tree, comprising the eight PS/TKs and the PTK clonedpreviously from G. cydonium, revealed that the PTK derived from the branchincluding the KRSvSD kinase. These data facilitate the first molecularapproach to elucidate the origin of metazoan PTK within the PS/TKsuperfamily.