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Crystal structures of the PLP‐ and PMP‐bound forms of BtrR, a dual functional aminotransferase involved in butirosin biosynthesis

2006; Wiley; Volume: 65; Issue: 1 Linguagem: Inglês

10.1002/prot.21076

1097-0134

Bojana Popovic, Xiao Tang, Dimitri Y. Chirgadze, Fanglu Huang, Tom L. Blundell, Jonathan B. Spencer,

Genomics and Phylogenetic Studies

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 Å and 1.7 Å 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 α helical N‐terminus, a central αβα sandwich domain and an αβ 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. Proteins 2006. © 2006 Wiley‐Liss, Inc.