NRMT2 is an N-terminal monomethylase that primes for its homologue NRMT1

Abstract

N-terminal RCC1 methyltransferase (NRMT) was the first eukaryotic methyltransferase identified to specifically methylate the free α-amino group of proteins. Since the discovery of this N-terminal methyltransferase, many new substrates have been identified and the modification itself has been shown to regulate DNA-protein interactions. Sequence analysis predicts one close human homolog of NRMT, Methyltransferase-like protein 11B (METTL11B, now renamed NRMT2). We show here for the first time that NRMT2 also has N-terminal methylation activity and recognizes the same N-terminal consensus sequences as NRMT (now NRMT1). Both enzymes have similar tissue expression and cellular localization patterns. However, enzyme assays and mass spectrometry experiments indicate they differ in their specific catalytic functions. While NRMT1 is a distributive methyltransferase that can mono-, di-, and trimethylate its substrates, NRMT2 is primarily a monomethylase. Concurrent expression of NRMT1 and NRMT2 accelerates the production of trimethylation, and we propose that NRMT2 activates NRMT1 by priming its substrates for trimethylation.

Kinetic Mechanism of Protein N-terminal Methyltransferase 1

“…NTMT2, a close homologue of NTMT1, has been reported to be primarily a monomethyltransferase (6). It was proposed that NTMT2 primes for NTMT1 by providing monomethylated substrates based on concurrent expression of NTMT1 and NTMT2 (6). Because the kinetic constants for unmethylated and monomethylated peptide substrates from our study are comparable, it is unlikely that NTMT1 is solely dependent on NTMT2 for the production of monomethylated peptide substrates.…”

“…NTMT2, a close homologue of NTMT1, has been reported to be primarily a monomethyltransferase (6). It was proposed that NTMT2 primes for NTMT1 by providing monomethylated substrates based on concurrent expression of NTMT1 and NTMT2 (6).…”

“…In 2010, the first two eukaryotic ␣-N-terminal protein methyltransferases were discovered; the Macara laboratory (4) identified NTMT1 2 / NRMT1/METTL11A from humans, and the Clarke laboratory (5) identified YBR261C/Tae1 from yeast. Recently, Schaner Tooley and co-workers (6) showed that NTMT2/NRMT2/ METTL11B also has ␣-N-terminal methylation activity.…”

The ribosome: A hot spot for the identification of new types of protein methyltransferases

“…Purified Ntm1 and its METTL11A human ortholog (now designated NTMT1) catalyzed the methylation of synthetic peptides with N-terminal proline, serine, or alanine residues followed by the proline-lysine sequence but no activity was seen with peptides where the proline in the second position or the lysine in the third position was substituted. The NTMT1 human enzyme was also identified at nearly the same time by the Macara laboratory and designated NRMT for Nterminal RCC1 methyltransferase based on one of its substrates (54) and later NRMT1 after a second human ortholog (METTL11B or NRTM2) was described (55). METTL11B was suggested to be primarily a monomethyltransferase that may prime substrates for the action of NTMT1 (55).…”

“…The NTMT1 human enzyme was also identified at nearly the same time by the Macara laboratory and designated NRMT for Nterminal RCC1 methyltransferase based on one of its substrates (54) and later NRMT1 after a second human ortholog (METTL11B or NRTM2) was described (55). METTL11B was suggested to be primarily a monomethyltransferase that may prime substrates for the action of NTMT1 (55). Crystal structures of human NTMT1 in complex with substrate peptides have been solved (56,57) that support the substrate specificity of this enzyme determined from kinetic (58,59) and inhibitor studies (60).…”