Proteomic analysis, purification and characterization of a new milk-clotting protease from Tenebrio molitor larvae

Abstract

Tenebrio molitor larvae is an edible insect with high protein content; researchers have extracted several proteases from gut of T. molitor larvae. However, information on the milk-clotting protease of T. molitor larvae remains unknown. We found that while most of the milk-clotting activity (MCA) was concentrated in the midgut (H) of T. molitor larvae, some activity was also seen in the hindgut (T). To evaluate the possible functional activity of the protease, we used TMT labelling-coupled with LC-MS/MS for proteomics analysis of T and H. The results showed that a total of 223 differentially expressed proteins (DEPs) between T and H. The upregulated proteins were enrich the cysteine-type endopeptidase and serine-type peptidase. A serine endopeptidase with a molecular mass of 29.681 kDa and a C/P value of 104.7 with milk-clotting activity was obtained from midgut of T. molitor larvae by ultrafiltration and multistage chromatography, and characterized by Edman degradation. The main cleavage site in κ-casein (κ-CN) was Lys116-Thr117 bond for the protease, as determined by mass spectrometry analysis. The protease had a Michaelis constant (Km) of 1.39 g/L, an optimal pH of 5.5, and an optimal temperature of 65 °C, indicating it could serve as a new milk coagulant and provide a theoretical basis for the development of insect chymosin.

Keywords

• Tenebrio molitor larvae
• Milk-clotting protease
• TMT
• Characteristics
• Serine protease
• Cleavage site