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Title:Structural studies of Butirosin D and FrbG
Author(s):Nguyen, Kim-Phung
Director of Research:Nair, Satish K.
Doctoral Committee Chair(s):Nair, Satish K.
Doctoral Committee Member(s):Morrissey, James H.; Hong, Jin; Huang, Raven H.
Department / Program:Biochemistry
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):Butirosin D
structural studies
Abstract:A structural homology model of Butirosin D is presented. This enzyme has been previously re-characterized as a deacetylase, releasing a free acetate molecule when acting upon the substrate 2’-N-acetylparomamine. The involved catalytic core residues within the model are 100% conserved, as compared to the crystal structure of Orf2* in complex with its ligand teicoplanin. A triad of two is histamine (H14 and H163) residues and one aspartic acid (D16) residue coordinate a metal ion, believed to act in concert with another aspartic acid residue (D19) as the Lewis acid for the reaction to occur. Residues surrounding this relatively deep motif are likely to direct both ligand specificity and registry, in particular residues A107, possibly Q193 and the capping loop. FR-900098 is a phosphonic acid derivative from the soil isolate Streptomyces rubellomurinus that has been shown to be effective against Plasmodium falciparum, a protozoan parasitic strain that causes a fatal form of malaria. The biosynthetic strategy for FR-900098 involves a novel coupling step in which intermediates in the pathway are conjugated to cytidine-5’-monophosphate (CMP) and the enzymes involved in the late steps of FR-900098 biosynthesis function only on the conjugated substrate. Here, we present the 1.6 Å resolution crystal structure and accompanying biochemical characterization of FrbG, which catalyzes the hydroxylation of CMP-conjugated aminopropylphosphonate. We show that FrbG is a novel enzyme that shares a similar function with known flavin-containing monooxygenases (FMOs) but is structurally distinct from these other prokaryotic and eukaryotic FMOs. Within the co-crystal structure, the prosthetic group FAD and NADP(H) cofactor (reduced form) are bound within a basic, continuous channel at the core of FrbG. FrbG is distinguished from typical FMOs in that the nucleotide cofactor-binding domain also serves in conferring substrate specificity. Notably, in contrasts to all other available FMO structures, the crystal structure presented here represents a catalytically active conformation, with the C4 of the NADP(H) nicotinamide situated near the N5 of the FAD isoalloxazine, poised for hydride transfer. A comparison with previously determined structures of FMOs in the post-hydride transfer conformation highlights structural rearrangements that may occur following the reduction of the flavin.
Issue Date:2014-09-16
Rights Information:Copyright 2014 Kim-Phung Nguyen
Date Available in IDEALS:2014-09-16
Date Deposited:2014-08

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