1dj9
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CRYSTAL STRUCTURE OF 8-AMINO-7-OXONANOATE SYNTHASE (OR 7-KETO-8AMINIPELARGONATE OR KAPA SYNTHASE) COMPLEXED WITH PLP AND THE PRODUCT 8(S)-AMINO-7-OXONANONOATE (OR KAPA). THE ENZYME OF BIOTIN BIOSYNTHETIC PATHWAY.
OverviewOverview
8-Amino-7-oxononanoate synthase (also known as 7-keto-8-aminopelargonate, synthase, EC 2.3.1.47) is a pyridoxal 5'-phosphate-dependent enzyme which, catalyzes the decarboxylative condensation of L-alanine with pimeloyl-CoA, in a stereospecific manner to form 8(S)-amino-7-oxononanoate. This is the, first committed step in biotin biosynthesis. The mechanism of Escherichia, coli AONS has been investigated by spectroscopic, kinetic, and, crystallographic techniques. The X-ray structure of the holoenzyme has, been refined at a resolution of 1.7 A (R = 18.6%, R(free) = 21. 2%) and, shows that the plane of the imine bond of the internal aldimine deviates, from the pyridine plane. The structure of the enzyme-product external, aldimine complex has been refined at a resolution of 2.0 A (R = 21.2%, R(free) = 27.8%) and shows a rotation of the pyridine ring with respect to, that in the internal aldimine, together with a significant conformational, change of the C-terminal domain and subtle rearrangement of the active, site hydrogen bonding. The first step in the reaction, L-alanine external, aldimine formation, is rapid (k(1) = 2 x 10(4) M(-)(1) s(-)(1)). Formation, of an external aldimine with D-alanine, which is not a substrate, is, significantly slower (k(1) = 125 M(-)(1) s(-)(1)). Binding of D-alanine to, AONS is enhanced approximately 2-fold in the presence of pimeloyl-CoA., Significant substrate quinonoid formation only occurs upon addition of, pimeloyl-CoA to the preformed L-alanine external aldimine complex and is, preceded by a distinct lag phase ( approximately 30 ms) which suggests, that binding of the pimeloyl-CoA causes a conformational transition of the, enzyme external aldimine complex. This transition, which is inferred by, modeling to require a rotation around the Calpha-N bond of the external, aldimine complex, promotes abstraction of the Calpha proton by Lys236., These results have been combined to form a detailed mechanistic pathway, for AONS catalysis which may be applied to the other members of the, alpha-oxoamine synthase subfamily.
About this StructureAbout this Structure
1DJ9 is a Single protein structure of sequence from Escherichia coli with SO4, MG and KAM as ligands. Active as 8-amino-7-oxononanoate synthase, with EC number 2.3.1.47 Full crystallographic information is available from OCA.
ReferenceReference
Mechanism of 8-amino-7-oxononanoate synthase: spectroscopic, kinetic, and crystallographic studies., Webster SP, Alexeev D, Campopiano DJ, Watt RM, Alexeeva M, Sawyer L, Baxter RL, Biochemistry. 2000 Jan 25;39(3):516-28. PMID:10642176
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