Download MendeleyStructural Basis of the Stereochemistry of Inhibition of Tryptophan Synthase by Tryptophan and Derivatives.
Phillips, R.S., Harris, A.P.(2021) Biochemistry 60: 231-244
- PubMed: 33428374
- DOI: https://doi.org/10.1021/acs.biochem.0c00635
- Primary Citation of Related Structures:
6XNC, 6XOY, 6XRH, 6XT0 - PubMed Abstract:
We have examined the reaction of Salmonella enterica serovar typhimurium tryptophan (Trp) synthase ¦Á 2 ¦Â 2 complex with l-Trp, d-Trp, oxindolyl-l-alanine (OIA), and dioxindolyl-l-alanine (DOA) in the presence of disodium (dl)-¦Á-glycerol phosphate (GP), using stopped-flow spectrophotometry and X-ray crystallography. All structures contained the d-isomer of GP bound at the ¦Á-active site. (3 S )-OIA reacts with the pyridoxal-5'-phosphate (PLP) of Trp synthase to form a mixture of external aldimine and quinonoid complexes. The ¦Á-carboxylate of OIA rotates about 90¡ã to become planar with the PLP when the quinonoid complex is formed, resulting in a conformational change in the loop of residues 110-115. The COMM domain of the Trp synthase-OIA complex is found as a mixture of two conformations. The (3 R )-diastereomer of DOA binds about 5-fold more tightly than (3 S )-OIA and also forms a mixture of aldimine and quinonoid complexes. DOA forms an additional H-bond between the 3-OH of DOA and ¦ÂLys-87. l-Trp does not form a covalent complex with the PLP of Trp synthase. However, d-Trp forms a mixture of two external aldimine complexes which differ in the orientation of the ¦Á-carboxylate. In one conformation, the ¦Á-carboxylate is in the plane of the PLP, while in the other conformation, the ¦Á-carboxylate is perpendicular to the PLP plane. These results confirm that the stereochemistry of the transient indolenine quinonoid intermediate in the mechanism of Trp synthase is (3 S ) and demonstrate the linkage between aldimine and quinonoid reaction intermediates in the ¦Â-active site and allosteric communications with the ¦Á-active site.
Organizational Affiliation:
Department of Chemistry, University of Georgia, Athens, Georgia 30602, United States.
