title: Molecular structure of WlbB, a bacterial N-acetyltransferase involved in the biosynthesis of 2,3-diacetamido-2,3-dideoxy-D-mannuronic acid .
abstract: The pathogenic bacteria Pseudomonas aeruginosa and Bordetella pertussis contain in their outer membranes the rare sugar 2,3-diacetamido-2,3-dideoxy-d-mannuronic acid. Five enzymes are required for the biosynthesis of this sugar starting from UDP-N-acetylglucosamine. One of these, referred to as WlbB, is an N-acetyltransferase that converts UDP-2-acetamido-3-amino-2,3-dideoxy-d-glucuronic acid (UDP-GlcNAc3NA) to UDP-2,3-diacetamido-2,3-dideoxy-d-glucuronic acid (UDP-GlcNAc3NAcA). Here we report the three-dimensional structure of WlbB from Bordetella petrii. For this analysis, two ternary structures were determined to 1.43 A resolution: one in which the protein was complexed with acetyl-CoA and UDP and the second in which the protein contained bound CoA and UDP-GlcNAc3NA. WlbB adopts a trimeric quaternary structure and belongs to the LbetaH superfamily of N-acyltransferases. Each subunit contains 27 beta-strands, 23 of which form the canonical left-handed beta-helix. There are only two hydrogen bonds that occur between the protein and the GlcNAc3NA moiety, one between O(delta1) of Asn 84 and the sugar C-3' amino group and the second between the backbone amide group of Arg 94 and the sugar C-5' carboxylate. The sugar C-3' amino group is ideally positioned in the active site to attack the si face of acetyl-CoA. Given that there are no protein side chains that can function as general bases within the GlcNAc3NA binding pocket, a reaction mechanism is proposed for WlbB whereby the sulfur of CoA ultimately functions as the proton acceptor required for catalysis.
authors.affiliation: Department of Biochemistry, University of Wisconsin, Madison, Wisconsin 53706, USA.
authors.forename: James B
authors.initials: JB
authors.lastname: Thoden
authors.forename: Hazel M
authors.initials: HM
authors.lastname: Holden
mesh_terms: D000105:Acetyl Coenzyme A / Q000737:chemistry; D000123:Acetyltransferases / Q000096:biosynthesis* / Q000737:chemistry* / Q000145:classification / Q000235:genetics / Q000502:physiology*; D001425:Bacterial Outer Membrane Proteins / Q000737:chemistry* / Q000145:classification / Q000502:physiology*; D001884:Bordetella / Q000201:enzymology* / Q000235:genetics; D002384:Catalysis; D020134:Catalytic Domain / Q000235:genetics; D003460:Crystallization; D018360:Crystallography, X-Ray; D020836:Protein Structure, Quaternary / Q000235:genetics; D013379:Substrate Specificity / Q000235:genetics; D014530:Uridine Diphosphate / Q000737:chemistry / Q000378:metabolism; D014574:Uronic Acids / Q000737:chemistry* / Q000145:classification / Q000378:metabolism
chemical_list: D001425:Bacterial Outer Membrane Proteins; D014574:Uronic Acids; D014530:Uridine Diphosphate; D000105:Acetyl Coenzyme A; C035278:2,3-diacetamido-2,3-dideoxymannuronic acid; D000123:Acetyltransferases