Heterologous overexpression and characterization of homoserine dehydrogenase from Paracoccidioides brasiliensis

Abstract

The enzyme Homoserine dehydrogenase from Paracoccidioides brasiliensis (PbHSD), an interesting enzyme in the search for new antifungal drugs against paracoccidioidomycosis, was expressed by E. coli. Thirty milligrams of PbHSD with 94% of purity were obtained per liter of culture medium. The analysis by CD spectroscopy indicates a composition of 45.5 ± 7.3% of α-helices and 10.5 ± 7.0% β-strands. Gel filtration chromatography indicates a homodimer as biological unity. Fluorescence emission spectroscopy has shown stability of PbHSD in the presence of urea until C_m of 4.13 ± 0.21 M, and a broad pH range in which there is no conformational change. The protein analysis by differential scanning calorimetry indicates high stability at room temperature, but low stability at high temperatures, suffering irreversible denaturation, with T_m = 58.65 ± 0.87 °C. Kinetic studies of PbHSD by molecular absorption spectroscopy in UV/Vis have shown an optimum pH between 9.35 and 9.50, with Michaelian behavior, presenting K_M of 224 ± 15 μM and specific activity at optimum pH of 2.10 ± 0.07 μmol/min/mg for homoserine. Therefore, protein expression and purification were efficient, and the structural characterization has shown that PbHSD presents native conformation with enzymatic activity in kinetic assays.

Keywords: Homoserine dehydrogenase; Paracoccidioidomycosis; Specific activity.