Identification of protein N-terminal methyltransferases in yeast and humans.
Protein modification by methylation is important in cellular function. We show here that the Saccharomyces cerevisiae YBR261C/TAE1 gene encodes an N-terminal protein methyltransferase catalyzing the modification of two ribosomal protein substrates, Rpl12ab and Rps25a/Rps25b. The YBR261C/Tae1 protein is conserved across eukaryotes; all of these proteins share sequence similarity with known seven beta-strand class I methyltransferases. Wild-type yeast cytosol and mouse heart cytosol catalyze the methylation of a synthetic peptide (PPKQQLSKY) that contains the first eight amino acids of the processed N-terminus of Rps25a/Rps25b. However, no methylation of this peptide is seen in yeast cytosol from a DeltaYBR261C/tae1 deletion strain. Yeast YBR261C/TAE1 and the human orthologue METTL11A genes were expressed as fusion proteins in Escherichia coli and were shown to be capable of stoichiometrically dimethylating the N-terminus of the synthetic peptide. Furthermore, the YBR261C/Tae1 and METTL11A recombinant proteins methylate variants of the synthetic peptide containing N-terminal alanine and serine residues. However, methyltransferase activity is largely abolished when the proline residue in position 2 or the lysine residue in position 3 is substituted. Thus, the methyltransferases described here specifically recognize the N-terminal X-Pro-Lys sequence motif, and we suggest designating the yeast enzyme Ntm1 and the human enzyme NTMT1. These enzymes may account for nearly all previously described eukaryotic protein N-terminal methylation reactions. A number of other yeast and human proteins also share the recognition motif and may be similarly modified. We conclude that protein X-Pro-Lys N-terminal methylation reactions catalyzed by the enzymes described here may be widespread in nature.
Webb
Kristofor J
KJ
Department of Chemistry and Biochemistry and Molecular Biology Institute, University of California, Los Angeles, 607 Charles E. Young Drive East, Los Angeles, California 90095, USA.
Lipson
Rebecca S
RS
Al-Hadid
Qais
Q
Whitelegge
Julian P
JP
Clarke
Steven G
SG
D000595:Amino Acid Sequence; D002851:Chromatography, High Pressure Liquid; D006801:Humans; D013058:Mass Spectrometry; D008745:Methylation; D008780:Methyltransferases / Q000737:chemistry* / Q000235:genetics; D008969:Molecular Sequence Data; D012269:Ribosomal Proteins / Q000737:chemistry / Q000302:isolation & purification; D012441:Saccharomyces cerevisiae / Q000201:enzymology*; D021241:Spectrometry, Mass, Electrospray Ionization
D012269:Ribosomal Proteins; D008780:Methyltransferases