The silkworm, Bombyx mori, is an important economic insect for its production of silk. The larvae of many lepidopteran insects are major agricultural pests and often silkworm is explored as a model organism for other lepidopteran pest species. The hemolymph of caterpillars contains a lot of nutrient and immune components. In this study, we applied liquid chromatography-tandem mass spectrometry to gain a better understanding of the larval hemolymph proteomics in B. mori. We identified 752 proteins in hemolymph collected from day-4 fourth instar and day-7 fifth instar. Nearly half the identified proteins (49%) were predicted to function as binding proteins and 46% were predicted to have catalytic activities. Apolipophorins, storage proteins, and 30K proteins constituted the most abundant groups of nutrient-storage proteins. Of them, 30K proteins showed large differences between fourth instar larvae and fifth instar larvae. Besides nutrient-storage proteins, protease inhibitors are also expressed very highly in hemolymph. The analysis also revealed lots of immunity-related proteins, including recognition, signaling, effectors and other proteins, comprising multiple immunity pathways in hemolymph. Our data provide an exhaustive research of nutrient-storage proteins and immunity-related proteins in larval hemolymph, and will pave the way for future physiological and pathological studies of caterpillars.

These authors contributed equally to this work.Keywords: characterization, CTLA4-Ig fusion protein, glycan, glycosylation modification, intact protein, mass spectrometry, peptide mapping, similarity CTLA4-Ig is a highly glycosylated therapeutic fusion protein that contains multiple N-and O-glycosylation sites. Glycosylation plays a vital role in protein solubility, stability, serum half-life, activity, and immunogenicity. For a CTLA4-Ig biosimilar development program, comparative analytical data, especially the glycosylation data, can influence decisions about the type and amount of animal and clinical data needed to establish biosimilarity. Because of the limited clinical experience with biosimilars before approval, a comprehensive level of knowledge about the biosimilar candidates is needed to achieve subsequent development. Liquid chromatography-mass spectrometry (LC-MS) is a versatile technique for characterizing N-and O-glycosylation modification of recombinant therapeutic proteins, including 3 levels: intact protein analysis, peptide mapping analysis, and released glycans analysis. In this report, an in-depth characterization of glycosylation of a candidate biosimilar was carried out using a systematic approach: N-and O-linked glycans were identified and electron-transfer dissociation was then used to pinpoint the 4 occupied O-glycosylation sites for the first time. As the results show, the approach provides a set of routine tools that combine accurate intact mass measurement, peptide mapping, and released glycan profiling. This approach can be used to comprehensively research a candidate biosimilar Fc-fusion protein and provides a basis for future studies addressing the similarity of CTLA4-Ig biosimilars.

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The development of the testis involves a large number of tissue-specific proteins, possibly because the sperms in it are the most divergent of all cell types. In this study, LC-MS/MS was employed to investigate the protein compositions of the adult testis of silkworm. A total of 14,431 peptides were identified in the adult testis of Bombyx mori, which were matched to 2292 proteins. Thirty-two HSPs constitute a group of most abundant proteins in the adult testis, suggesting that they are critical for the development, differentiation, and survival of germ cells. Other proteins in this analysis were also involved in testis-specific processes mainly including sperm motility, meiosis, germ cell development, and spermatogenesis. The data have been deposited to the ProteomeXchange with identifier PXD000909 (http://proteomecentral.proteomexchange.org/dataset/PXD000909).