title: Crystal structures of the PLP- and PMP-bound forms of BtrR, a dual functional aminotransferase involved in butirosin biosynthesis.
abstract: The aminotransferase (BtrR), which is involved in the biosynthesis of butirosin, a 2-deoxystreptamine (2-DOS)-containing aminoglycoside antibiotic produced by Bacillus circulans, catalyses the pyridoxal phosphate (PLP)-dependent transamination reaction both of 2-deoxy-scyllo-inosose to 2-deoxy-scyllo-inosamine and of amino-dideoxy-scyllo-inosose to 2-DOS. The high-resolution crystal structures of the PLP- and PMP-bound forms of BtrR aminotransferase from B. circulans were solved at resolutions of 2.1 A and 1.7 A with R(factor)/R(free) values of 17.4/20.6 and 19.9/21.9, respectively. BtrR has a fold characteristic of the aspartate aminotransferase family, and sequence and structure analysis categorises it as a member of SMAT (secondary metabolite aminotransferases) subfamily. It exists as a homodimer with two active sites per dimer. The active site of the BtrR protomer is located in a cleft between an alpha helical N-terminus, a central alphabetaalpha sandwich domain and an alphabeta C-terminal domain. The structures of the PLP- and PMP-bound enzymes are very similar; however BtrR-PMP lacks the covalent bond to Lys192. Furthermore, the two forms differ in the side-chain conformations of Trp92, Asp163, and Tyr342 that are likely to be important in substrate selectivity and substrate binding. This is the first three-dimensional structure of an enzyme from the butirosin biosynthesis gene cluster.
authors.affiliation: Department of Biochemistry, University of Cambridge, Cambridge, United Kingdom.
authors.forename: Bojana
authors.initials: B
authors.lastname: Popovic
authors.forename: Xiao
authors.initials: X
authors.lastname: Tang
authors.forename: Dimitri Y
authors.initials: DY
authors.lastname: Chirgadze
authors.forename: Fanglu
authors.initials: F
authors.lastname: Huang
authors.forename: Tom L
authors.initials: TL
authors.lastname: Blundell
authors.forename: Jonathan B
authors.initials: JB
authors.lastname: Spencer
mesh_terms: D000595:Amino Acid Sequence; D001407:Bacillus / Q000201:enzymology; D001665:Binding Sites; D003198:Computer Simulation; D003460:Crystallization; D018360:Crystallography, X-Ray; D006860:Hydrogen Bonding; D008958:Models, Molecular; D011485:Protein Binding; D011732:Pyridoxal Phosphate / Q000737:chemistry*; D011733:Pyridoxamine / Q000031:analogs & derivatives* / Q000737:chemistry; D000637:Transaminases / Q000737:chemistry*
chemical_list: D011732:Pyridoxal Phosphate; D011733:Pyridoxamine; C513572:BtrR aminotransferase, Bacillus circulans; D000637:Transaminases; C010627:pyridoxamine phosphate