Visualization of Pronation States in PLP Dependent Enzymes

Abstract

Pyridoxal phosphate (PLP) dependent enzymes are essential proteins that catalyze a diverse number of reactions: transamination, racemization, phosphorylation, decarboxylation, aldol cleavage, elimination, and replacement. Despite completing a myriad of chemical reactions, these proteins have a unifying Schiff base catalytic intermediate but the overall mechanisms remain ambiguous. Based upon previous X‐ray structures and abundant literature of the different families of PLP dependent enzymes, one question must be answered: How do the different families of PLP dependent enzymes utilize different protonation profiles of pyridoxal phosphate that enable them to promote catalysis of a specific reaction? The objective of this research will be development of detailed model mechanisms for the different classes of PLP dependent enzymes, based on the protonation state of the coenzyme. Aspartate aminotransferase (AAT) and tryptophan synthase (TS) are two model PLP dependent enzymes that have shown to grow neutron diffraction quality crystals (1mm3). Neutron crystallography is an unparalleled tool to determine the atomic coordinates of the hydrogen/deuterium in macromolecules undetectable by other means. Initial neutron data collection and refinement of these proteins gives insight to the protonation state of PLP during catalysis.