Biochemical and spectroscopic properties ofBrucella microti glutamate decarboxylase, a key component of the glutamate‐dependent acid resistance system

Abstract

Herein, biochemical and spectroscopic properties of GadB fromBrucella microti (BmGadB), aBrucella species which possesses GDAR, are described.B. microti belongs to a group of lately described and atypical brucellae that possess functionalgadB andgadC genes, unlike the most well‐known “classical”Brucella species, which include important human pathogens.BmGadB is hexameric at acidic pH. The pH‐dependent spectroscopic properties and activity profile, combined within silico sequence comparison withE. coli GadB (EcGadB), suggest thatBmGadB has the necessary structural requirements for the binding of activating chloride ions at acidic pH and for the closure of its active site at neutral pH. On the contrary, cellular localization analysis, corroborated by sequence inspection, suggests thatBmGadB does not undergo membrane recruitment at acidic pH, which was observed inEcGadB. The comparison of GadB from evolutionary distant microorganisms suggests that for this enzyme to be functional in GDAR some structural features must be preserved.

Keywords

• Brucella microti
• Glutamate decarboxylase
• Cooperativity
• pH-dependent activity
• Chloride activation
• Substituted aldamine