 |
PDBsum entry 1s5t
|
|
|
|
|
 |
Contents |
 |
|
|
|
|
|
|
|
|
|
|
* Residue conservation analysis
|
|
|
|
|
References listed in PDB file
|
|
|
Key reference
|
|
|
Title
|
|
The crystal structure of three site-Directed mutants of escherichia coli dihydrodipicolinate synthase: further evidence for a catalytic triad.
|
|
|
Authors
|
|
R.C.Dobson,
K.Valegård,
J.A.Gerrard.
|
|
|
Ref.
|
|
J Mol Biol, 2004,
338,
329-339.
[DOI no: ]
|
|
|
PubMed id
|
|
|
|
|
|
Abstract
|
|
|
Dihydrodipicolinate synthase (DHDPS, EC 4.2.1.52) catalyses the branchpoint
reaction of lysine biosynthesis in plants and microbes: the condensation of
(S)-aspartate-beta-semialdehyde and pyruvate. The crystal structure of wild-type
DHDPS has been published to 2.5A, revealing a tetrameric molecule comprised of
four identical (beta/alpha)(8)-barrels, each containing one active site.
Previous workers have hypothesised that the catalytic mechanism of the enzyme
involves a catalytic triad of amino acid residues, Tyr133, Thr44 and Tyr107,
which provide a proton shuttle to transport protons from the active site to
solvent. We have tested this hypothesis using site-directed mutagenesis to
produce three mutant enzymes: DHDPS-Y133F, DHDPS-T44V and DHDPS-Y107F. Each of
these mutants has substantially reduced activity, consistent with the catalytic
triad hypothesis. We have determined each mutant crystal structure to at least
2.35A resolution and compared the structures to the wild-type enzyme. All mutant
enzymes crystallised in the same space group as the wild-type form and only
minor differences in structure are observed. These results suggest that the
catalytic triad is indeed in operation in wild-type DHDPS.
|
|
|
|
|
|
|
|
Figure 2.
Figure 2. Putative roles for the catalytic triad in the
mechanism of DHDPS. This mechanism has been adapted from Hutton
et al.[33.]
|
|
Figure 5.
Figure 5. Stereo-view showing overlays of the active sites
of wild-type (black) and mutant DHDPS structures (gold).
Electron density covers the mutated residue in each image and is
contoured to 1s. Shown from top to bottom: a, DHDPS-Y133F; b,
DHDPS-T44V; c, DHDPS-Y107F. The images were generated using
O[31.] and Molray. [35.]
|
|
|
|
|
|
The above figures are
reprinted
by permission from Elsevier:
J Mol Biol
(2004,
338,
329-339)
copyright 2004.
|
|
|
|
|
|
|
