Submitted to: Comparative Biochemistry and Physiology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 10/19/2011
Publication Date: 2/1/2012
Citation: Goptar, I.A., Semashko, T.A., Danilenko, S.A., Lysogorskaya, E.N., Oksenoit, E.S., Zhuzhikov, D.P., Belozersky, M.A., Dunaevsky, Y.E., Oppert, B.S., Filippova, I.Y., Elpidina, E.N. 2012. Cysteine digestive peptidases function as post-glutamine cleaving enzymes in tenebrionid stored product pests. Comparative Biochemistry and Physiology, Part B. 161(2): 148-154. http://dx.doi.org/10.1016/j.cbpb.2011.10.005. Interpretive Summary: To be successful, stored product pests need to have enzymes capable of efficiently digesting their main dietary proteins, which have many glutamine and proline amino acids. We describe for the first time enzymes, glutamine-specific peptidases, in the gut of yellow mealworm larvae that are capable of digesting proteins at glutamine residues. Our characterization of these peptidases indicates that they are previously studied enzymes belonging to the class of cysteine peptidases, hypothesized to have evolved in storage pests to protect the insect from serine protease inhibitors found in cereals. We now propose that storage pests also have retained cysteine peptidases to efficiently digest cereal proteins. These results may be exploited to develop new control products for storage pests.
Technical Abstract: Cereals have storage proteins with high amounts of the amino acids glutamine and proline. Therefore, storage pests need to have digestive enzymes that are efficient in hydrolyzing these types of proteins. Post-glutamine cleaving peptidases (PGP) were isolated from the midgut of the stored product pest, Tenebrio molitor (yellow mealworm). Three distinct PGP activities were found using the highly-specific chromogenic peptide substrate N-benzyloxycarbonyl-L-Ala-L-Ala-L-Gln p-nitroanilide: PGP1PM and PGP2PM in the posterior midgut, and PGP2AM in the anterior midgut. The peptidases in each group were characterized according to their gel elution times, activity profiles in buffers of different pH, electrophoretic mobility under native conditions, and inhibitor sensitivity. The results indicate that PGP activity is due to cysteine and not serine chymotrypsin-like peptidases operating in the T. molitor larval midgut. We propose that the evolutionary conservation of cysteine peptidases in the complement of digestive peptidases of tenebrionid stored product beetles is due not only to the adaptation of insects to plants rich in serine peptidase inhibitors, but also to accommodate the need to efficiently cleave major dietary proteins rich in glutamine.