Structural and functional diversities in lepidopteran serine proteases

Abstract

Primary protein-digestion in Lepidopteran larvae relies on serine proteases like trypsin and chymotrypsin. Efforts toward the classification and characterization of digestive proteases have unraveled a considerable diversity in the specificity and mechanistic classes of gut proteases. Though the evolutionary significance of mutations that lead to structural diversity in serine proteases has been well characterized, detailing the resultant functional diversity has continually posed a challenge to researchers. Functional diversity can be correlated to the adaptation of insects to various host-plants as well as to exposure of insects to naturally occurring antagonistic biomolecules such as plant-derived protease inhibitors (PIs) and lectins. Current research is focused on deciphering the changes in protease specificities and activities arising from altered amino acids at the active site, specificity-determining pockets and other regions, which influence activity. Some insight has been gained through in silico modeling and simulation experiments, aided by the limited availability of characterized proteases. We examine the structurally and functionally diverse Lepidopteran serine proteases, and assess their influence on larval digestive processes and on overall insect physiology.

Isolation and in vitro identification of proteinase inhibitors from soybean seeds inhibiting helicoverpa gut proteases

“…Trypsin and serine proteases are key enzymes in the digestive system of the lepidopterian insects showing about 95% of the total digestive activity (Srinivasan et al 2006;Liu et al 2009). Inhibiting the insect digestive proteases will lead to the strong physiological stress on the insect for the availability of the essential amino acids.…”

A chymotrypsin-like serine protease interacts with the chitin synthase from the midgut of the tobacco hornworm

“…Insect midgut proteases may therefore act not only to digest nutrients but also to specifically modulate non-digestive gut enzymes such as chitin synthase, which is necessary for peritrophic matrix production. This notion may also be important for a better understanding of the structural and functional diversity of insect midgut proteases, particularly observed in lepidopteran systems (Srinivasan et al, 2006). Thus, protease inhibitors produced by plants as a defence against herbivorous insects could interfere not only with digestive gut proteases but also with intestinal proteolytic signalling cascades controlling chitin synthesis and thus peritrophic matrix formation, which is necessary to protect the insect digestive tract from mechanical damage and infection by pathogens.…”

Genomic and cDNA Cloning, Expression, Purification, and Characterization of Chymotrypsin-Trypsin Inhibitor from Winged Bean Seeds

“…41) Although the P1 residue of the inhibitor is the most important site of proteinase-PI contact, 42) extended binding interactions between the inhibitor and protease might also contribute to the stability of the association. 43) The mutant proteins can be utilized by site-directed mutagenesis to investigate the contribution of Leu (63) and Arg (64) in chymotrypsin and trypsin inhibition of WbCTI respectively.…”