title: Amalgamation of nucleosides and amino acids in antibiotic biosynthesis: discovery of an L-threonine:uridine-5'-aldehyde transaldolase.
abstract: The lipopeptidyl nucleoside antibiotics represented by A-90289, caprazamycin, and muraymycin are structurally highlighted by a nucleoside core that contains a nonproteinogenic β-hydroxy-α-amino acid named 5'-C-glycyluridine (GlyU). Bioinformatic analysis of the biosynthetic gene clusters revealed a shared open reading frame encoding a protein with sequence similarity to serine hydroxymethyltransferases, resulting in the proposal that this shared enzyme catalyzes an aldol-type condensation with glycine and uridine-5'-aldehyde to furnish GlyU. Using LipK involved in A-90289 biosynthesis as a model, we now functionally assign and characterize the enzyme responsible for the C-C bond-forming event during GlyU biosynthesis as an l-threonine:uridine-5'-aldehyde transaldolase. Biochemical analysis revealed this transformation is dependent upon pyridoxal-5'-phosphate, the enzyme has no activity with alternative amino acids, such as glycine or serine, as aldol donors, and acetaldehyde is a coproduct. Structural characterization of the enzyme product is consistent with stereochemical assignment as the threo diastereomer (5'S,6'S)-GlyU. Thus this enzyme orchestrates C-C bond breaking and formation with concomitant installation of two stereocenters to make a new l-α-amino acid with a nucleoside side chain.
authors.affiliation: Department of Pharmaceutical Sciences, College of Pharmacy, University of Kentucky, Lexington, 40536, United States.
authors.forename: Sandra
authors.initials: S
authors.lastname: Barnard-Britson
authors.forename: Xiuling
authors.initials: X
authors.lastname: Chi
authors.forename: Koichi
authors.initials: K
authors.lastname: Nonaka
authors.forename: Anatol P
authors.initials: AP
authors.lastname: Spork
authors.forename: Nidhi
authors.initials: N
authors.lastname: Tibrewal
authors.forename: Anwesha
authors.initials: A
authors.lastname: Goswami
authors.forename: Pallab
authors.initials: P
authors.lastname: Pahari
authors.forename: Christian
authors.initials: C
authors.lastname: Ducho
authors.forename: Jurgen
authors.initials: J
authors.lastname: Rohr
authors.forename: Steven G
authors.initials: SG
authors.lastname: Van Lanen
mesh_terms: D000447:Aldehydes / Q000378:metabolism*; D000900:Anti-Bacterial Agents / Q000096:biosynthesis* / Q000737:chemistry; D055162:Biocatalysis; D019295:Computational Biology; D008968:Molecular Conformation; D009705:Nucleosides / Q000737:chemistry / Q000378:metabolism*; D013912:Threonine / Q000378:metabolism*; D014153:Transaldolase / Q000378:metabolism*; D014529:Uridine / Q000378:metabolism*
chemical_list: D000447:Aldehydes; D000900:Anti-Bacterial Agents; D009705:Nucleosides; D013912:Threonine; D014153:Transaldolase; D014529:Uridine