P-21 Function and Origin of Pseudoenzymes within the Metallocarboxypeptidase Family

The M14 family of metallocarboxypeptidases (MCPs) is a large family of proteins. Most of these proteins function as proteolytic enzymes by trimming specific amino acids from the carboxy termini of substrate proteins. However, several members of this protein family lack enzymatic activity due to the substitution of critical active site amino acids. These pseudoenzymes are poorly characterized due to the lack of enzymatic activity. Recently we have attempted to learn more about the function of two such pseudoenzymes, S. cerevisiae Ecm14 and D. rerio Cpxm1a. In order to investigate the function of Ecm14, we employed a synthetic lethal assay, in which random mutagenesis of yeast was used to identify genes whose function was required in the absence of Ecm14. Screening of 27,000 yeast identified 22 putative synthetic lethal mutants which are currently being analyzed. In order to investigate the function of the vertebrate pseudoenzyme, Cpxm1a, we obtained a zebrafish containing a point mutation that resulted in the premature truncation of the protein. Following development of a genotyping method, we have begun the preliminary characterization of a craniofacial phenotype in this organism. It is apparent that pseudoenzymes have important function in biology. The origin of these functional pseudoenzymes is thought to be the duplication of an active enzyme gene followed by mutation. Through an analysis of the almost 200 vertebrate genomes found in the Ensembl database, we have identified many unique MCP gene duplications, with the expectation that some will encode new enzymes or pseudoenzymes.