Plant defense-inducing A'-acylglutamines from insect guts: structural diversity and microbe-assisted biosynthesis

摘要

N-Acylglutamines are ubiquitously present in the regurgitants of herbivorous insects. The compounds comprise a larger family containing fatty acids of different degrees of unsaturation and chain length. Further modifications occur in the fatty acid moiety by oxidative transformations to secondary alcohols and epoxides. By hydrolysis (epoxide), acylation or phosphorylation of the alcohols the diversity of the compounds is further increased. Screening of cultivable gut bacteria from several Lepidopterans revealed that many of the commensal microorganims are principally able to synthesize the N-acylglutamines. From Microbacterium arborescens the first pure N-acyl synthase was isolated and characterized as an homooligomeric enyzme with a protomer size of 17.2 kDa. The enzyme displays a pH optimum at pH 8 and second plateau of even higher activity between pH 9-12 corresponding to the strongly alkaline conditions in the insect gut. The enzyme catalyses amide formation between a wide range of free fatty acid and most proteinogenic amino acids. Preceding activation of the acyl moiety is not required.