title: Study of bacteriophage T4-encoded Dam DNA (adenine-N6)-methyltransferase binding with substrates by rapid laser UV cross-linking.
abstract: DNA methyltransferases of the Dam family (including bacteriophage T4-encoded Dam DNA (adenine-N(6))-methyltransferase (T4Dam)) catalyze methyl group transfer from S-adenosyl-L-methionine (AdoMet), producing S-adenosyl-L-homocysteine (AdoHcy) and methylated adenine residues in palindromic GATC sequences. In this study, we describe the application of direct (i.e. no exogenous cross-linking reagents) laser UV cross-linking as a universal non-perturbing approach for studying the characteristics of T4Dam binding with substrates in the equilibrium and transient modes of interaction. UV irradiation of the enzyme.substrate complexes using an Nd(3+):yttrium aluminum garnet laser at 266 nm resulted in up to 3 and >15% yields of direct T4Dam cross-linking to DNA and AdoMet, respectively. Consequently, we were able to measure equilibrium constants and dissociation rates for enzyme.substrate complexes. In particular, we demonstrate that both reaction substrates, specific DNA and AdoMet (or product AdoHcy), stabilized the ternary complex. The improved substrate affinity for the enzyme in the ternary complex significantly reduced dissociation rates (up to 2 orders of magnitude). Several of the parameters obtained (such as dissociation rate constants for the binary T4Dam.AdoMet complex and for enzyme complexes with a nonfluorescent hemimethylated DNA duplex) were previously inaccessible by other means. However, where possible, the results of laser UV cross-linking were compared with those of fluorescence analysis. Our study suggests that rapid laser UV cross-linking efficiently complements standard DNA methyltransferase-related tools and is a method of choice to probe enzyme-substrate interactions in cases in which data cannot be acquired by other means.
authors.affiliation: Federal State Research Institute State Research Center of Virology and Biotechnology Vector, Novosibirsk 630559, Russia.
authors.forename: Alexey A
authors.initials: AA
authors.lastname: Evdokimov
authors.forename: Bianca
authors.initials: B
authors.lastname: Sclavi
authors.forename: Victor V
authors.initials: VV
authors.lastname: Zinoviev
authors.forename: Ernst G
authors.initials: EG
authors.lastname: Malygin
authors.forename: Stanley
authors.initials: S
authors.lastname: Hattman
authors.forename: Malcolm
authors.initials: M
authors.lastname: Buckle
mesh_terms: D004247:DNA / Q000737:chemistry*; D019175:DNA Methylation / Q000528:radiation effects*; D007834:Lasers; D008958:Models, Molecular; D011485:Protein Binding; D012435:S-Adenosylhomocysteine / Q000737:chemistry / Q000378:metabolism; D012436:S-Adenosylmethionine / Q000737:chemistry / Q000378:metabolism; D015265:Site-Specific DNA-Methyltransferase (Adenine-Specific) / Q000737:chemistry* / Q000378:metabolism; D013379:Substrate Specificity / Q000528:radiation effects; D014466:Ultraviolet Rays; D014764:Viral Proteins / Q000737:chemistry* / Q000378:metabolism
chemical_list: D014764:Viral Proteins; D012436:S-Adenosylmethionine; D004247:DNA; D012435:S-Adenosylhomocysteine; C058693:Dam methyltransferase; D015265:Site-Specific DNA-Methyltransferase (Adenine-Specific); C499297:dam protein, Bacteriophage T4