title: Structure of the YibK methyltransferase from Haemophilus influenzae (HI0766): a cofactor bound at a site formed by a knot.
abstract: The crystal structures of YibK from Haemophilus influenzae (HI0766) have been determined with and without bound cofactor product S-adenosylhomocysteine (AdoHcy) at 1.7 and 2.0 A resolution, respectively. The molecule adopts an alpha/beta fold, with a topology that differs from that of the classical methyltransferases. Most notably, HI0766 contains a striking knot that forms the binding crevice for the cofactor. The knot formation is correlated with an alternative arrangement of the secondary structure units compared with the classical methyltransferases. Two loop regions undergo conformational changes upon AdoHcy binding. In contrast to the extended conformation of the cofactor seen in the classical methyltransferase structures, AdoHcy binds to HI0766 in a bent conformation. HI0766 and its close sequence relatives are all shorter versions of the more remotely related rRNA/tRNA methyltransferases of the spoU sequence family. We propose that the spoU sequence family contains the same core domain for cofactor binding as HI0766 but has an additional domain for substrate binding. The substrate-binding domain is absent in HI0766 sequence family and may be provided by another Haemophilus influenzae partner protein, which is yet to be identified.
authors.affiliation: Center for Advanced Research in Biotechnology, University of Maryland Biotechnology Institute, Rockville, MD 20850, USA.
authors.forename: Kap
authors.initials: K
authors.lastname: Lim
authors.forename: Hong
authors.initials: H
authors.lastname: Zhang
authors.forename: Aleksandra
authors.initials: A
authors.lastname: Tempczyk
authors.forename: Wojciech
authors.initials: W
authors.lastname: Krajewski
authors.forename: Nicklas
authors.initials: N
authors.lastname: Bonander
authors.forename: John
authors.initials: J
authors.lastname: Toedt
authors.forename: Andrew
authors.initials: A
authors.lastname: Howard
authors.forename: Edward
authors.initials: E
authors.lastname: Eisenstein
authors.forename: Osnat
authors.initials: O
authors.lastname: Herzberg
mesh_terms: D000595:Amino Acid Sequence; D001665:Binding Sites; D018360:Crystallography, X-Ray; D006193:Haemophilus influenzae / Q000201:enzymology*; D008780:Methyltransferases / Q000737:chemistry* / Q000378:metabolism; D008958:Models, Molecular; D008969:Molecular Sequence Data; D015394:Molecular Structure; D011487:Protein Conformation; D017433:Protein Structure, Secondary; D012435:S-Adenosylhomocysteine / Q000737:chemistry / Q000378:metabolism*; D016415:Sequence Alignment
chemical_list: D012435:S-Adenosylhomocysteine; D008780:Methyltransferases