The Tryptophan Synthase α2β2 Complex: A Model for Substrate Channeling, Allosteric Communication, and Pyridoxal Phosphate Catalysis

I reflect on my research on pyridoxal phosphate (PLP) enzymes over fifty-five years and on how I combined research with marriage and family. My Ph.D. research with Esmond E. Snell established one aspect of PLP enzyme mechanism. My postdoctoral work first with Hans L. Kornberg and then with Alton Meister characterized the structure and function of another PLP enzyme, L-aspartate beta-decarboxylase. My independent research at the National Institutes of Health (NIH) since 1966 has focused on the bacterial tryptophan synthase alpha(2)beta(2) complex. The beta subunit catalyzes a number of PLP-dependent reactions. We have characterized these reactions and the allosteric effects of the alpha subunit. We also used chemical modification to probe enzyme structure and function. Our crystallization of the tryptophan synthase alpha(2)beta(2) complex from Salmonella typhimurium led to the determination of the three-dimensional structure with Craig Hyde and David Davies at NIH in 1988. This landmark structure was the first structure of a multienzyme complex and the first structure revealing an intramolecular tunnel. The structure has provided a basis for exploring mechanisms of catalysis, channeling, and allosteric communication in the tryptophan synthase alpha(2)beta(2) complex. The structure serves as a model for many other multiprotein complexes that are important for biological processes in prokaryotes and eukaryotes.