Processive versus distributive methyl group transfer was assessed for pea Rubisco large subunit methyltransferase, a SET domain protein lysine methyltransferase catalyzing the formation of trimethyllysine-14 in the large subunit of Rubisco. Catalytically competent complexes between an immobilized form of des(methyl) Rubisco and Rubisco large subunit methyltransferase were used to demonstrate enzyme release that was co-incident with and dependent on formation of trimethyllysine. Catalytic rate constants determined for formation of trimethyllysine were considerably lower ( approximately 10-fold) than rate constants determined for total radiolabel incorporation from [3H-methyl]-S-adenosylmethionine. Double-reciprocal velocity plots under catalytic conditions favoring monomethyllysine indicated a random or ordered reaction mechanism, while conditions favoring trimethyllysine suggested a hybrid ping-pong mechanism. These results were compared with double-reciprocal velocity plots and product analyses obtained for HsSET7/9 (a monomethyltransferase) and SpCLR4 (a dimethyltransferase) and suggest a predictive ability of double-reciprocal velocity plots for single versus multiple methyl group transfers by SET domain protein lysine methyltransferases. A model is proposed for SET domain protein lysine methyltransferases in which initial binding of polypeptide substrate and S-adenosylmethionine is random, with polypeptide binding followed by deprotonation of the epsilon-amine of the target lysyl residue and subsequent methylation. Following methyl group transfer, S-adenosylhomocysteine and monomethylated polypeptide dissociate from monomethyltransferases, but di- and trimethyltransferases begin a successive and catalytically obligatory deprotonation of enzyme-bound methylated lysyl intermediates, which along with binding and release of S-adenosylmethionine and S-adenosylhomocysteine is manifested as a hybrid ping-pong-like reaction mechanism.
Processive versus distributive methyl group transfer was assessed for pea Rubisco large subunit methyltransferase , a SET domain protein lysine methyltransferase catalyzing the formation of trimethyllysine-14 in the large subunit of Rubisco . Catalytically competent complexes between an immobilized form of des(methyl ) Rubisco and Rubisco large subunit methyltransferase were used to demonstrate enzyme release that was co - incident with and dependent on formation of trimethyllysine . Catalytic rate constants determined for formation of trimethyllysine were considerably lower ( approximately 10-fold ) than rate constants determined for total radiolabel incorporation from [ 3H - methyl]-S - adenosylmethionine . Double - reciprocal velocity plots under catalytic conditions favoring monomethyllysine indicated a random or ordered reaction mechanism , while conditions favoring trimethyllysine suggested a hybrid ping - pong mechanism . These results were compared with double - reciprocal velocity plots and product analyses obtained for HsSET7/9 ( a monomethyltransferase ) and SpCLR4 ( a dimethyltransferase ) and suggest a predictive ability of double - reciprocal velocity plots for single versus multiple methyl group transfers by SET domain protein lysine methyltransferases . A model is proposed for SET domain protein lysine methyltransferases in which initial binding of polypeptide substrate and S - adenosylmethionine is random , with polypeptide binding followed by deprotonation of the epsilon - amine of the target lysyl residue and subsequent methylation . Following methyl group transfer , S - adenosylhomocysteine and monomethylated polypeptide dissociate from monomethyltransferases , but di- and trimethyltransferases begin a successive and catalytically obligatory deprotonation of enzyme - bound methylated lysyl intermediates , which along with binding and release of S - adenosylmethionine and S - adenosylhomocysteine is manifested as a hybrid ping - pong - like reaction mechanism .
What is the characteristic domain of histone methyltransferases?
What is the characteristic domain of histone methyltransferases ?
SET domain
SET domain