Phosphoproteomic analysis of the posterior silk gland of Bombyx mori provides novel insight into phosphorylation regulating the silk production

Abstract

To understand phosphorylation event regulating silk synthesis in the posterior silk gland of Bombyx mori, phosphoproteome was profiled in a pair of near-isogenic lines, a normally cocooning strain (IC) and a nakedly pupated strain (IN) that the silk production is much lower than IC. In the posterior silk gland of the IC and IN, 714 and 658 phosphosites resided on 554 and 507 phosphopeptides from 431 and 383 phosphoproteins, were identified, respectively. Of all the phosphosites, the single phosphosite was the dominate phosphorylation form, comprising>60% of all the phosphosites in two phenotypic of silk production. All these phosphosites were classified as acidophilic and proline-directed kinase classes, and three motifs were uniquely identified in the IC. The motif S-P-P might be important for regulating phosphorylation network of silk protein synthesis. The dynamically phosphorylated proteins participated in ribosome, protein transport and energy metabolism suggest that phosphorylation may play key roles in regulating silk protein synthesis and secretion. Furthermore, fibroin heavy chain, an important component of silk protein, was specifically phosphorylated in the IC strain, suggesting its role to ensure the normal formation of silk structure and silk secretion. The data gain new understanding of the regulatory processes of silk protein synthesis and offer as starting point for further research on the silk production at phosphoproteome level. Significance of this studyDespite the knowledge on regulation of silk protein synthesis in the posterior silk gland has gained at the gene or protein levels, how phosphorylation event influences the silk yield is largely unknown. To this end, we constructed a pair of silkworm near-isogenic lines that showed different cocooning phenotypes, and the phosphoproteome of the posterior silk gland of two isolines was compared. Here, we reported the first phosphoproteome data on the silkworm and found several key pathways related protein synthesis are regulated by phosphorylation, thereby influencing the silk production. The data provide valuable resources for further functional assay of targeted protein phosphorylation that regulates the silk synthesis in silkworm.