Protein engineering of a cold-adapted rhamnogalacturonan acetylesterase: In vivo functional expression and cinnamyl acetate synthesis

Abstract

The rhamnogalacturonan acetylesterase gene (named pp1113), encoding a novel cold-adapted rhamnogalacturonan acetylesterase, was cloned from Paenibacillus polymyxa. pp1113 was functionally expressed in Escherichia coli by inducing expression at 20 °C for 16 h. The pH and temperature optimums for the recombinant enzyme were 8.5 and 30 °C, respectively. As an SGNH-type acetylesterase, pp1113 demonstrated high activity against acetyl ester substrates and could maintain approximately 60 % activity at 0 °C.The specific activity of purified pp1113 was 65.95 U/mg (C2). The Km and Vmax values of purified pp1113 were 3.89 mM and 81.07 μmol/min, respectively. We obtained an R232L variant with improved thermal stability and catalytic activity through site-directed mutagenesis. T1/2 of R232L at 50 °C increased from less than 30 min to 6 h when compared to wild-type pp1113, and T1/2 extended to 8 h after immobilization. The R232L mutant improved the conversion rate of 0.1 M cinnamyl alcohol at 40 °C to 94 % in the reaction of synthesis of cinnamyl acetate. After purification, the R232L mutant was immobilized (pH 8.0 phosphate buffer 0.5 M, 20 h at 20 °C, protein loading reached 17 mg/g). This was the first report of the rhamnogalacturonan acetylesterase gene obtained from Paenibacillus polymyxa with detailed enzymatic properties.