1A50: Crystal Structure Of Wild-Type Tryptophan Synthase Complexed With 5- Fluoroindole Propanol Phosphate

Citation:
Abstract
Crystal structures of wild-type tryptophan synthase alpha2beta2 complexes from Salmonella typhimurium were determined to investigate the mechanism of allosteric activation of the alpha-reaction by the aminoacrylate intermediate formed at the beta-active site. Using a flow cell, the aminoacrylate (A-A) intermediate of the beta-reaction () was generated in the crystal under steady state conditions in the presence of serine and the alpha-site inhibitor 5-fluoroindole propanol phosphate (F-IPP). A model for the conformation of the Schiff base between the aminoacrylate and the beta-subunit cofactor pyridoxal phosphate (PLP) is presented. The structure is compared with structures of the enzyme determined in the absence (TRPS) and presence (TRPSF-IPP) of F-IPP. A detailed model for binding of F-IPP to the alpha-subunit is presented. In contrast to findings by Hyde et al. [(1988) J. Biol. Chem. 263,17857-17871] and Rhee et al. [(1997) Biochemistry 36, 7664-7680], we find that the presence of an alpha-site alone ligand is sufficient for loop alphaL6 closure atop the alpha-active site. Part of this loop, alphaThr183, is important not only for positioning the catalytic alphaAsp60 but also for coordinating the concomitant ordering of loop alphaL2 upon F-IPP binding. On the basis of the three structures, a pathway for communication between the alpha- and beta-active sites has been established. The central element of this pathway is a newly defined rigid, but movable, domain that on one side interacts with the alpha-subunit via loop alphaL2 and on the other side with the beta-active site. These findings provide a structural basis for understanding the allosteric properties of tryptophan synthase.
PDB ID: 1A50Download
MMDB ID: 9761
PDB Deposition Date: 1998/2/18
Updated in MMDB: 2011/11
Experimental Method:
x-ray diffraction
Resolution: 2.3  Å
Source Organism:
Similar Structures:
Biological Unit for 1A50: tetrameric; determined by author
Molecular Components in 1A50
Label Count Molecule
Proteins (4 molecules)
2
Tryptophan Synthase (Alpha Chain)(Gene symbol: trpA)
Molecule annotation
2
Tryptophan Synthase (Beta Chain)(Gene symbol: trpB)
Molecule annotation
Chemicals (6 molecules)
1
2
2
2
3
2
* Click molecule labels to explore molecular sequence information.

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