A N-ALPHA-ACETYLTRANSFERASE SELECTIVELY TRANSFERS AN ACETYL GROUP TO NH2-TERMINAL METHIONINE RESIDUES - PURIFICATION AND PARTIAL CHARACTERIZATION

Methionine N-alpha-acetyltransferase (M-N(alpha)AT), which selectively catalyzes the transfer of an acetyl group from acetyl coenzyme A to t he alpha-NH2 group of methionine residues in proteins and peptides, wa s isolated from Saccharomyces cerevisiae. The enzyme was purified 22 0 00-fold to apparent homogeneity by successive purification steps using DEAE-Sepharose, DE-52 cellulose, CM-52 cellulose, Affi-Gel Blue gel a nd hydroxyapatite. The M(r) of the native enzyme was estimated to be 7 0 000 +/- 5000 by gel filtration chromatography. The enzyme has a pI n ear 8.3 as determined by chromatofocusing on Mono P. The enzyme cataly zed the transfer of an acetyl group to a synthetic peptide mimicking t he first 24 residues of yeast proteinase A inhibitor 3 (Met-Asn-Thr... ) and 3 of its 19 penultimately substituted analogues ([Asp(2)], [Glu( 2)], and [Gln(2)]). Based on the estimated molecular weight and amino- acid sequence, The enzyme is different from two other recently identif ied methionine N-alpha-acetyltransferases, NAT2 (Kulkarni, M.S. and Sh erman, F. (1994) J. Biol. Chem. 269, 13141-13147) and MAK3 (Tercero, J .C. and Wickner, R.B. (1992) J. Biol. Chem. 267, 20277-20281). Among t hese three enzymes, M-N(alpha)AT and NAT2 have similar substrate speci ficity, however, only purified M-N(alpha)AT, but not recombinant NAT2 gene product, can catalyze the transfer of acetyl group to NH2-termina l methionine residues. The availability of this methionine N-alpha-ace tyltransferase will advance the understanding of protein co-translatio nal processing.