2gin
X-ray structure of the wt allene oxide cyclase 2 from arabidopsis thaliana
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OverviewOverview
We describe the crystallization and structure elucidation of Arabidopsis, thaliana allene oxide cyclase 2 (AOC2), a key enzyme in the biosynthesis, of jasmonates. In a coupled reaction with allene oxide synthase, AOC2, releases the first cyclic and biologically active metabolite, 12-oxo-phytodienoic acid (OPDA). AOC2 (AT3G25770) folds into an, eight-stranded antiparallel beta-barrel with a C-terminal partial helical, extension. The protein forms a hydrophobic binding cavity with two, distinct polar patches. AOC2 is trimeric in crystals, in vitro and in, planta. Based on the observed folding pattern, we assigned AOC2 as a low, molecular weight member of the lipocalin family with enzymatic activity in, plants. We determined the binding position of the competitive inhibitor, vernolic acid (a substrate analog) in the binding pocket. Based on models, for bound substrate 12,13-epoxy-9,11,15-octadecatrienoic acid and product, OPDA, we propose a reaction scheme that explains the influence of the C15, double bond on reactivity. Reaction is promoted by anchimeric assistance, through a conserved Glu residue. The transition state with a pentadienyl, carbocation and an oxyanion is stabilized by a strongly bound water, molecule and favorable pi-pi interactions with aromatic residues in the, cavity. Stereoselectivity results from steric restrictions to the, necessary substrate isomerizations imposed by the protein.
About this StructureAbout this Structure
2GIN is a Single protein structure of sequence from Arabidopsis thaliana with NA and GOL as ligands. Active as Allene-oxide cyclase, with EC number 5.3.99.6 Full crystallographic information is available from OCA.
ReferenceReference
The crystal structure of Arabidopsis thaliana allene oxide cyclase: insights into the oxylipin cyclization reaction., Hofmann E, Zerbe P, Schaller F, Plant Cell. 2006 Nov;18(11):3201-17. Epub 2006 Nov 3. PMID:17085685
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