1qgn
From Proteopedia
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CYSTATHIONINE GAMMA-SYNTHASE FROM NICOTIANA TABACUM
Overview
Cystathionine gamma-synthase catalyses the committed step of de novo, methionine biosynthesis in micro-organisms and plants, making the enzyme, an attractive target for the design of new antibiotics and herbicides. The, crystal structure of cystathionine gamma-synthase from Nicotiana tabacum, has been solved by Patterson search techniques using the structure of, Escherichia coli cystathionine gamma-synthase. The model was refined at, 2.9 A resolution to a crystallographic R -factor of 20.1 % (Rfree25.0 %)., The physiological substrates of the enzyme, L-homoserine phosphate and, L-cysteine, were modelled into the unliganded structure. These complexes, support the proposed ping-pong mechanism for catalysis and illustrate the, dissimilar substrate specificities of bacterial and plant cystathionine, gamma-synthases on a molecular level. The main difference arises from the, binding modes of the distal substrate groups (O -acetyl/succinyl versusO, -phosphate). Central in fixing the distal phosphate of the plant CGS, substrate is an exposed lysine residue that is strictly conserved in plant, cystathionine gamma-synthases whereas bacterial enzymes carry a glycine, residue at this position. General insight regarding the reaction, specificity of transsulphuration enzymes is gained by the comparison to, cystathionine beta-lyase from E. coli, indicating the mechanistic, importance of a second substrate binding site for L-cysteine which leads, to different chemical reaction types.
About this Structure
1QGN is a Single protein structure of sequence from Nicotiana tabacum with PLP as ligand. Active as Cystathionine gamma-synthase, with EC number 2.5.1.48 Full crystallographic information is available from OCA.
Reference
The crystal structure of cystathionine gamma-synthase from Nicotiana tabacum reveals its substrate and reaction specificity., Steegborn C, Messerschmidt A, Laber B, Streber W, Huber R, Clausen T, J Mol Biol. 1999 Jul 30;290(5):983-96. PMID:10438597
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