Methylation of key biological molecules plays important roles in numerous systems, including signal transduction, biosynthesis, protein repair, gene silencing, and chromatin regulation.¹ The S-adenosylmethionine (SAM)-dependent methyltransferases use SAM, also known as AdoMet, as a methyl group donor for the modification of both proteins and DNA.² Aberrant levels of SAM have been linked to many abnormalities, including Alzheimer’s Disease, depression, Parkinson’s Disease, multiple sclerosis, liver failure, and cancer.^1,2 SET Domain-containing Protein 7/9 (SET7/9; lysine methyltransferase 7 (KMT7)) is a methyltransferase that acts on various substrates including histone 3 at lysine residue 4 (H3K4), p53, and the transcription factor TAF 10.³ Lysine residues can be mono-, di-, or tri-methylated. Unlike most SET proteins, SET7/9 is exclusively a mono-methylase.⁴ Methylation of lysine residues can promote transcriptional activation or repression and is critical for regulating histone function.⁵ SET7/9 methylation of p53 in response to DNA damage activates p53 for subsequent acetylation.⁵ SET7/9 is able to modulate p53 activity in a human cancer cell line, implying that it may play a significant role in human turmorigenesis. Cayman’s SET7/9 Methyltransferase Inhibitor Screening Assay provides a convenient method for screening human SET7/9 inhibitors. The transfer of the methyl group from SAM by SET7/9 to the acceptor peptide (TAF 10) generates S-adenosylhomocysteine, which is rapidly converted to S-ribosylhomocysteine and adenine by adenosylhomocysteine nucleosidase. This rapid conversion prevents the buildup of adenosylhomocysteine and its feedback inhibition on the methylation reaction. Finally, the adenine is converted to hypoxanthine by adenine deaminase, which in turn is converted to urate and hydrogen peroxide (H₂O₂). The reaction between H₂O₂ and ADHP (10-acetyl-3,7-dihydroxyphenoxazine) produces the highly fluorescent compound resorufin. Resorufin fluorescence is analyzed using an excitation wavelength of 530-540 nm and an emission wavelength of 585-595 nm.

1 Loenen, W.A.M. S-Adenosylmethionine: Jack of all trades and master of everything?. Biochem Soc Trans 34(2) 330-333 (2006).

2 Chiang, P.K., Gordon, R.K., Tal, J., et al. S-adenosylmethionine and methylation. FASEB J 10 471-480 (1996).

3 Couture, J., Collazo, E., Hauk, G., et al. Structural basis for the methylation site specificity of SET7/9. Nat Struct Mol Biol 13(2) 140-146 (2006).

4 Xiao, B., Jing, C., Wilson, J.R., et al. Structure and catalytic mechanism of the human histone methyltransferase SET7/9. Nature 421 652-656 (2003).

5 Kurash, J.K., Lei, H., Shen, Q., et al. Methylation of p53 by Set7/9 mediates p53 acetylation and activity in vivo. Mol Cell 29 392-400 (2008).

Loenen, W.A.M. S-Adenosylmethionine: Jack of all trades and master of everything?. Biochem Soc Trans 34(2) 330-333 (2006).

Song, M., Ghosh, A. FGF2-induced chromatin remodeling regulates CNTF-mediated gene expression and astrocyte differentiation. Nat Neurosci 7(3) 229-235 (2004).

Couture, J., Collazo, E., Hauk, G., et al. Structural basis for the methylation site specificity of SET7/9. Nat Struct Mol Biol 13(2) 140-146 (2006).

Dorgan, K.M., Wooderchak, W.L., Wynn, D.P., et al. An enzyme-coupled continuous spectrophotometric assay for S-adenosylmethionine-dependent methyltransferases. Anal Biochem 350 249-255 (2006).

Kurash, J.K., Lei, H., Shen, Q., et al. Methylation of p53 by Set7/9 mediates p53 acetylation and activity in vivo. Mol Cell 29 392-400 (2008).

Chiang, P.K., Gordon, R.K., Tal, J., et al. S-adenosylmethionine and methylation. FASEB J 10 471-480 (1996).

Xiao, B., Jing, C., Wilson, J.R., et al. Structure and catalytic mechanism of the human histone methyltransferase SET7/9. Nature 421 652-656 (2003).

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