Crystal structure of wild-type tryptophan synthase complexed with the natural substrate indole-3-glycerol phosphate.
We used freeze trapping to stabilize the Michaelis complex of wild-type tryptophan synthase and the alpha-subunit substrate indole-3-glycerol phosphate (IGP) and determined its structure to 1. 8 A resolution. In addition, we determined the 1.4 A resolution structure of the complex with indole-3-propanole phosphate (IPP), a noncleavable IGP analogue. The interaction of the 3'-hydroxyl of IGP with the catalytic alphaGlu49 leads to a twisting of the propane chain and to a repositioning of the indole ring compared to IPP. Concomitantly, the catalytic alphaAsp60 rotates resulting in a translocation of the COMM domain [betaGly102-betaGly189, for definition see Schneider et al. (1998) Biochemistry 37, 5394-5406] in a direction opposite to the one in the IPP complex. This results in loss of the allosteric sodium ion bound at the beta-subunit and an opening of the beta-active site, thereby making the cofactor pyridoxal 5'-phosphate (PLP) accessible to solvent and thus serine binding. These findings form the structural basis for the information transfer from the alpha- to the beta-subunit and may explain the affinity increase of the beta-active site for serine upon IGP binding.
Weyand
M
M
Max-Planck-Institute for Molecular Physiology, Department of Physical Biochemistry, Dortmund, Germany.
Schlichting
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D001665:Binding Sites; D003198:Computer Simulation; D018360:Crystallography, X-Ray; D005994:Glycerophosphates / Q000737:chemistry* / Q000378:metabolism; D007202:Indicators and Reagents; D007211:Indoles / Q000737:chemistry / Q000378:metabolism; D008958:Models, Molecular; D010446:Peptide Fragments / Q000737:chemistry / Q000378:metabolism; D011487:Protein Conformation; D017434:Protein Structure, Tertiary; D012964:Sodium / Q000737:chemistry / Q000378:metabolism; D013379:Substrate Specificity; D014367:Tryptophan Synthase / Q000737:chemistry* / Q000378:metabolism
D005994:Glycerophosphates; D007202:Indicators and Reagents; D007211:Indoles; D010446:Peptide Fragments; C041272:indolepropanol phosphate; C008117:indoleglycerol phosphate; D012964:Sodium; D014367:Tryptophan Synthase