Expression of a metagenome-derived fumarate reductase from marine microorganisms and its characterization

A potential novel fumarate reductase gene designated frd1A was isolated by screening a marine metagenomic library through a sequence-based strategy. Sequence analyses indicated that Frd1A and other putative fumarate reductases were closely related. The putative fumarate reductase gene was subcloned into a pETBlue-2 vector and expressed in Escherichia coli Tuner(DE3)pLacІ cells. The recombinant protein was purified to homogeneity. Functional characterization by high-performance liquid chromatography demonstrated that the recombinant Frd1A protein could catalyze the hydrogenation of fumarate to succinate acid. The Frd1A protein displayed an optimal activity at pH 7.0 and 28 °C, which could be stimulated by adding metal ions such as Zn2+ and Mg2+. The Frd1A enzyme showed a comparable affinity and catalytic efficiency under optimal reaction conditions: km =0.227 mmol/L, vmax= 29.9 U/mg, and kcat/km=5.44 × 104 per mol/s. The identification of Frd1A protein underscores the potential of marine metagenome screening for novel biomolecules.