1qgn
CYSTATHIONINE GAMMA-SYNTHASE FROM NICOTIANA TABACUM
OverviewOverview
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 StructureAbout this Structure
1QGN is a Single protein structure of sequence from Nicotiana tabacum. Full crystallographic information is available from OCA.
ReferenceReference
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 Page seeded by OCA on Sat May 3 06:14:51 2008