Crystal structure of pyruvate decarboxylase fromZymobacter palmae

Abstract

Pyruvate decarboxylase (PDC; EC 4.1.1.1) is a thiamine pyrophosphate- and Mg2+ion-dependent enzyme that catalyses the non-oxidative decarboxylation of pyruvate to acetaldehyde and carbon dioxide. It is rare in bacteria, but is a key enzyme in homofermentative metabolism, where ethanol is the major product. Here, the previously unreported crystal structure of the bacterial pyruvate decarboxylase fromZymobacter palmaeis presented. The crystals were shown to diffract to 2.15 Å resolution. They belonged to space groupP21, with unit-cell parametersa= 204.56,b= 177.39,c= 244.55 Å andRr.i.m.= 0.175 (0.714 in the highest resolution bin). The structure was solved by molecular replacement using PDB entry 2vbi as a model and the finalRvalues wereRwork= 0.186 (0.271 in the highest resolution bin) andRfree= 0.220 (0.300 in the highest resolution bin). Each of the six tetramers is a dimer of dimers, with each monomer sharing its thiamine pyrophosphate across the dimer interface, and some contain ethylene glycol mimicking the substrate pyruvate in the active site. Comparison with other bacterial PDCs shows a correlation of higher thermostability with greater tetramer interface area and number of interactions.