Protein Profiles of the Midgut of Spodoptera litura Larvae at the Sixth Instar Feeding Stage by Shotgun ESI-MS Approach

By using shotgun HPLC-ESI-MS proteomics approach, 2043 peptides were identified from the midgut of Spodoptera litura larvae at the sixth instar feeding stage, out of which 1489 (72.9%) were found to have their homologues in the public protein databases and 842 had identities of molecular functions. Seven-hundred forty-one peptides were annotated according to Gene Ontology Annotation in terms of molecular function, biological process, and cellular localization, with 336 and 251 peptides being related to catalytic activity and binding activity, respectively. Most of the catalytic proteins had activity of hydrolases, oxidoreductases and transferases and most of the binding proteins were involved in protein-binding activity. Among the annotated peptides, 487 were classified into different cellular processes and 490 were classified to locate in the cytoplasm. Nonredundant enzymes associated with the metabolisms of carbohydrates, lipids and fatty acids, amino acids and proteins, translation, transport, and stress resistance were identified. Presence and expression at high levels of numerous enzymes of glycolysis pathway, synthesis of proteins, and absorption and transport of fatty acids and lipids indicate that active metabolism processes of carbohydrates, proteins, and lipids occurred in the midgut of sixth instar feeding larvae of S. litura. The protein profile provides a basis for further study of the physiological events in the midgut of S. litura.