Characterization of Novel Acetyltransferases Found in Budding and Fission Yeasts That Detoxify a Proline Analogue, Azetidine-2-Carboxylic Acid

We recently found that budding yeast Saccharomyces cerevisiae Σ1278b, but not genome project strain S288C, has a gene conferring resistance to l-azetidine-2-carboxylic acid (AZC), a toxic four-membered ring analogue of l-proline. Also, the gene, designated as MPR1, encodes a novel acetyltransferase that detoxifies AZC via acetylation. We now report the results of subsequent work. On a homology search with MPR1, we detected a gene in fission yeast Schizosaccharomyces pombe. This gene, designated as ppr1+ (pombe MPR1), is responsible for the AZC-resistance of S. pombe as judged from the results of gene disruption and overexpression experiments. Escherichia coli cells expressing ppr1+, like ones expressing MPR1, were resistant to AZC and produced an AZC acetyltransferase. We further found that the enzymes encoded by MPR1 and ppr1+ were homodimers, and catalyzed the acetylation of AZC but not any other l-proline–related compounds. Ppr1p was more thermostable than Mpr1p, although Ppr1p had a lower optimum temperature than Mpr1p. The higher AZC acetylation activity of Mpr1p, in comparison to that of Ppr1p, was attributed to the larger kcat/Km value for acetyl-CoA of Mpr1p than that of Ppr1p.