title: Manipulating unconventional CH-based hydrogen bonding in a methyltransferase via noncanonical amino acid mutagenesis.
abstract: Recent studies have demonstrated that the active sites of S-adenosylmethionine (AdoMet)-dependent methyltransferases form strong carbon-oxygen (CH···O) hydrogen bonds with the substrate's sulfonium group that are important in AdoMet binding and catalysis. To probe these interactions, we substituted the noncanonical amino acid p-aminophenylalanine (pAF) for the active site tyrosine in the lysine methyltransferase SET7/9, which forms multiple CH···O hydrogen bonds to AdoMet and is invariant in SET domain enzymes. Using quantum chemistry calculations to predict the mutation's effects, coupled with biochemical and structural studies, we observed that pAF forms a strong CH···N hydrogen bond to AdoMet that is offset by an energetically unfavorable amine group rotamer within the SET7/9 active site that hinders AdoMet binding and activity. Together, these results illustrate that the invariant tyrosine in SET domain methyltransferases functions as an essential hydrogen bonding hub and cannot be readily substituted by residues bearing other hydrogen bond acceptors.
authors.affiliation: Howard Hughes Medical Institute , Ann Arbor, Michigan 48109, United States.
authors.forename: Scott
authors.initials: S
authors.lastname: Horowitz
authors.forename: Upendra
authors.initials: U
authors.lastname: Adhikari
authors.forename: Lynnette M A
authors.initials: LM
authors.lastname: Dirk
authors.forename: Paul A
authors.initials: PA
authors.lastname: Del Rizzo
authors.forename: Ryan A
authors.initials: RA
authors.lastname: Mehl
authors.forename: Robert L
authors.initials: RL
authors.lastname: Houtz
authors.forename: Hashim M
authors.initials: HM
authors.lastname: Al-Hashimi
authors.forename: Steve
authors.initials: S
authors.lastname: Scheiner
authors.forename: Raymond C
authors.initials: RC
authors.lastname: Trievel
mesh_terms: D000596:Amino Acids / Q000737:chemistry*; D002384:Catalysis; D006860:Hydrogen Bonding; D008780:Methyltransferases / Q000737:chemistry*; D016296:Mutagenesis; D011789:Quantum Theory; D012436:S-Adenosylmethionine / Q000737:chemistry
chemical_list: D000596:Amino Acids; D012436:S-Adenosylmethionine; D008780:Methyltransferases