Expression, Purification and Partial Characterization of Recombinant S-Adenosyl-L-Homocysteine Hydrolase from Banana

We have recently identified S-adenosyl-L-homocysteine hydrolase (SAHH) as a novel banana allergen with a potentially decisive role in the development of cross-reactivity between plant-derived food and respiratory allergens. The recalcitrant nature of banana pulp and intrinsically low abundance of SAHH limit its production from natural sources. Our objective was to optimize production and biochemically characterize recombinant banana SAHH (rSAHH) with implications for the food safety industry, food allergy diagnosis and treatment, and basic research in molecular allergology. rSAHH with C-terminal 6His tag was successfully expressed in Escherichia coli BL21(DE3) cells, and purified to homogeneity by immobilized metal affinity chromatography (IMAC), yielding 10 mg of rSAHH/L of cell culture under optimized conditions. It is functional as a monomer with an approximate molecular weight of 55 kDa and pI of 5.83. Structural integrity, IgE reactivity, and biological activity of rSAHH were confirmed by Western blot and standard colorimetric SAHH assay with Ellman's reagent, respectively. As a mesophilic enzyme with wide pH stability and high 8-month storage stability, rSAHH obtained in this study is the promising candidate for further diagnostic and therapeutic applications. To the author's best knowledge, rSAHH is the only recombinantly produced plant-derived SAHH thus far.