title: Function of Pro-185 in the ProCys of conserved motif IV in the EcoRII [cytosine-C5]-DNA methyltransferase.
abstract: ProCys in the conserved sequence motif IV of [cytosine-C5]-DNA methyltransferases is known to be part of the catalytic site. The Cys residue is directly involved in forming a covalent bond with the C6 of the target cytosine. We have found that substitution of Pro-185 with either Ala or Ser resulted in a reduced rate of methyl group transfer by the EcoRII DNA methyltransferase. In addition, we observed an increase in the Km for substrate S-adenosyl-L-methionine (AdoMet), but a decrease in the Km for substrate DNA. This is reflected in minor changes in kcat/Km for DNA, but in 10- to 100-fold reductions in kcat/Km for AdoMet. This suggests that Pro-185 is important to properly orient the activated cytosine and AdoMet for methyl group transfer by direct interaction with AdoMet and indirectly via the Cys interaction with cytosine.
authors.affiliation: Department of Biology, University of Rochester, NY 14627, USA.
authors.forename: V G
authors.initials: VG
authors.lastname: Kossykh
authors.forename: S L
authors.initials: SL
authors.lastname: Schlagman
authors.forename: S
authors.initials: S
authors.lastname: Hattman
mesh_terms: D000595:Amino Acid Sequence; D001665:Binding Sites; D003001:Cloning, Molecular; D017124:Conserved Sequence; D003545:Cysteine; D004247:DNA / Q000378:metabolism; D015257:DNA-Cytosine Methylases / Q000737:chemistry* / Q000302:isolation & purification / Q000378:metabolism*; D004926:Escherichia coli / Q000201:enzymology*; D007700:Kinetics; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D011392:Proline; D011994:Recombinant Proteins / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism; D012436:S-Adenosylmethionine / Q000378:metabolism; D013379:Substrate Specificity
chemical_list: D011994:Recombinant Proteins; D012436:S-Adenosylmethionine; D004247:DNA; D011392:Proline; C029528:DNA modification methylase EcoRII; D015257:DNA-Cytosine Methylases; D003545:Cysteine