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PDBsum entry 1a5a
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Contents |
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* Residue conservation analysis
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References listed in PDB file
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Key reference
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Title
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Cryo-Crystallography of a true substrate, Indole-3-Glycerol phosphate, Bound to a mutant (alphad60n) tryptophan synthase alpha2beta2 complex reveals the correct orientation of active site alphaglu49.
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Authors
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S.Rhee,
E.W.Miles,
D.R.Davies.
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Ref.
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J Biol Chem, 1998,
273,
8553-8555.
[DOI no: ]
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PubMed id
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Abstract
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The reversible cleavage of indole-3-glycerol by the alpha-subunit of tryptophan
synthase has been proposed to be catalyzed by alphaGlu49 and alphaAsp60.
Although previous x-ray crystallographic structures of the tryptophan synthase
alpha2beta2 complex showed an interaction between the carboxylate of alphaAsp60
and the bound inhibitor indole-3-propanol phosphate, the carboxylate of
alphaGlu49 was too distant to play its proposed role. To clarify the structural
and functional roles of alphaGlu49, we have determined crystal structures of a
mutant (alphaD60N) alpha2beta2 complex in the presence and absence of the true
substrate, indole-3-glycerol phosphate. The enzyme in the crystal cleaves
indole-3-glycerol phosphate very slowly at room temperature but not under
cryo-conditions of 95 K. The structure of the complex with the true substrate
obtained by cryo-crystallography reveals that indole-3-glycerol phosphate and
indole-3-propanol phosphate have similar binding modes but different torsion
angles. Most importantly, the side chain of alphaGlu49 interacts with 3-hydroxyl
group of indole-3-glycerol phosphate as proposed. The movement of the side chain
of alphaGlu49 into an extended conformation upon binding the true substrate
provides evidence for an induced fit mechanism. Our results demonstrate how
cryo-crystallography and mutagenesis can provide insight into enzyme mechanism.
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Figure 1.
Fig. 1. A, the final 2F[o]  F[c] map
overlaid on the models of IGP and residues  Glu49 and
Tyr175 in
the D60N-IGP
complex. The map was contoured at 0.6  . B,
superposition between IGP (open circles) in the D60N-IGP
and IPP (filled circles) in the  K87T-Ser-IPP
complex (7). The carboxylate of Asp60 is
shown near the indole nitrogen of IPP and of IGP.
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The above figure is
reprinted
by permission from the ASBMB:
J Biol Chem
(1998,
273,
8553-8555)
copyright 1998.
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