Histidine carboxylase of Leuconostoc oenos 9204: Purification, kinetic properties, cloning and nucleotide sequence of the hdc gene

Abstract

Histidine decarboxylase (HDC) was purified to homogeneity from Leuconostoc oenos 9204, a wine lactic acid bacterium. Histidine decarboxylase comprised two subunits, respectively α and β. The hdc gene was cloned and sequenced. The gene encodes a single polypeptide of 315 amino acids, demonstrating that Leuc. oenos 9204 HDC was synthesized as a precursor proHDC π6 (Mr 205 000). A cleavage between Ser-81 and Ser-82 generated the α (Mr 25 380) and β (Mr 8840) chains, which suggested that the holoenzyme exists as a hexameric structure (αβ)6. At the optimal pH of 4.8, the HDC activity exhibited a simple Michaelis-Menten kinetic (K(m) = 0.33 mmol l-1, V(max) = 17.8 μmol CO2 min-1 mg-1), while at pH 7.6 it was sigmoidal (cooperativity index of 2). Histamine acted as a competitive inhibitor (K(i) = 32 mmol 1-1). The similarities of these results with those described for other bacterial HDC support the assumption that the pyruvoyl enzymes evolved from a common ancestral protein and have similar catalytic mechanisms. These results also confirmed that the main lactic acid bacterial species responsible for malolactic fermentation in red wine is able to produce histamine. Bacteria carrying the HDC activity must be avoided during selection of strains for the production of malolactic starters.