PDBsum entry 1a5a

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Lyase PDB id
Protein chains
255 a.a. *
389 a.a. *
Waters ×394
* Residue conservation analysis

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Title 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.
Authors S.Rhee, E.W.Miles, D.R.Davies.
Ref. J Biol Chem, 1998, 273, 8553-8555. [DOI no: 10.1074/jbc.273.15.8553]
PubMed id 9535826
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.
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.
The above figure is reprinted by permission from the ASBMB: J Biol Chem (1998, 273, 8553-8555) copyright 1998.
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