Biodegradation of Free Gossypol by Helicoverpa armigera Carboxylesterase Expressed in Pichia pastoris

Abstract

Gossypol is a polyphenolic toxic secondary metabolite derived from cotton. Free gossypol in cotton meal is remarkably harmful to animals. Furthermore, microbial degradation of gossypol produces metabolites that reduce feed quality. We adopted an enzymatic method to degrade free gossypol safely and effectively. We cloned the gene <i>cce001a</i> encoding carboxylesterase (CarE) into pPICZαA and transformed it into <i>Pichia pastoris</i> GS115. The target protein was successfully obtained, and CarE <i>CCE001a</i> could effectively degrade free gossypol with a degradation rate of 89%. When esterase was added, the exposed toxic groups of gossypol reacted with different amino acids and amines to form bound gossypol, generating substances with (M + H) <i>m</i>/<i>z</i> ratios of 560.15, 600.25, and 713.46. The molecular formula was C₂₇H₂₈O₁₃, C₃₄H₃₆N₂O₆, and C₄₇H₅₉N₃O₃. The observed instability of the hydroxyl groups caused the substitution and shedding of the group, forming a substance with <i>m</i>/<i>z</i> of 488.26 and molecular formula C₃₁H₃₆O₅. These properties render the CarE <i>CCE001a</i> a valid candidate for the detoxification of cotton meal. Furthermore, the findings help elucidate the degradation process of gossypol in vitro.