|
type |
Journal Article |
authors |
Steegborn, C.; Messerschmidt, A.; Laber, B.; Streber, W.; Huber, R.; Clausen, T. |
title |
The crystal structure of cystathionine gamma-synthase from Nicotiana tabacum reveals its substrate and reaction specificity |
journal |
J Mol Biol |
Activity |
2.5.1.48 |
Family |
2.5.1.48.b |
sel |
selected |
ui |
10438597 |
year |
(1999) |
volume |
290 |
number |
5 |
pages |
983-96 |
| |
keywords |
Crystal |
abstract |
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. |
last changed |
2009/02/11 18:04 |
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