Integument

Oxidative conjugation of catechols for insect cuticle sclerotization

K. J. Kramer 1 , M. R. Kanost 2 , T. L. Hopkins 3 , H. Jiang 2 , R. Suderman 2 , R. Xu 3

1 Grain Marketing and Production Research Center, ARS, USDA, Manhattan, KS 66502, USA; 2 Dept. of Biochemistry and 3 Entomology, Kansas State University, Manhattan, KS 66506, USA

Cuticle sclerotization or tanning is a vital process that occurs during each stage of insect development to harden and stabilize the newly secreted exoskeleton. The structural polymers, protein and chitin, make up the bulk of the cuticle, and chemical interactions between these biopolymers with quinonoid tanning agents are largely responsible for the final properties of the exoskeleton. The main hypothesis for sclerotization involves the formation of cross-links between nucleophilic imidazole nitrogens of histidyl residues in cuticular proteins and electrophilic ring or side chain carbons of ortho-quinones and para-quinone methides derived from two catechols, N-beta-alanyldopamine and 3,4-dihydroxyphenylethanol. C-N and C-O linkages between tanning agents and proteins in a variety of insect cuticles from several orders of insects have been elucidated. cDNAs for both the tyrosinase and laccase types of phenoloxidases that catalyze the cross-linking reactions have been isolated and sequenced. The sequences of laccase cDNAs from two insect species demonstrate that insect laccases are more similar to fungal laccases than to those from plants. These results provide insight into how insects use structural proteins, catechols, and oxidative enzymes to form catechol-amino acid adducts, which help to stabilize their exoskeletons. This research was supported in part by the National Science Foundation.

Index terms: Manduca sexta, Anopheles gambiae, cross-linking, oxidation, metabolism.

More Topics on the Wing

About Us