1A5A

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 ALPHA GLU 49

Summary for 1A5A

• Entry DOI: 10.2210/pdb1a5a/pdb
• Descriptor: TRYPTOPHAN SYNTHASE (ALPHA CHAIN), TRYPTOPHAN SYNTHASE (BETA CHAIN), POTASSIUM ION, ... (5 entities in total)
• Functional Keywords: carbon-oxygen lyase, mutation at position 60 (asp --> asn) in the a-subunit, lyase
• Biological source: Salmonella typhimurium; More
• Total number of polymer chains: 2
• Total formula weight: 71957.09

Authors

Rhee, S.,Miles, E.W.,Davies, D.R. (deposition date: 1998-02-12, release date: 1998-05-27, Last modification date: 2021-11-03)

Primary citation

Rhee, S.,Miles, E.W.,Davies, D.R.
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.
J.Biol.Chem., 273:8553-8555, 1998

PubMed Abstract: 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.

PubMed: 9535826
DOI: 10.1074/jbc.273.15.8553

Experimental method

X-RAY DIFFRACTION (1.9 Å)