Dimerization of ER-resident molecular chaperones mediated by ERp29

The development of silk glands and transcriptome aberration induced by cyantraniliprole in Bombyx mori

Bombyx mori is an insect species of great economic importance, and its silk gland is a vital organ for the synthesis and secretion of silk protein. However, long-term artificial domestication of B. mori has resulted in high sensitivity to chemical toxins, especially insecticides. Cyantraniliprole (Cya), a second-generation ryanodine receptor modulator insecticide, is widely utilized in agriculture for pest control. In this study, the impact of Cya toxicity on the development of silk glands in the 5th instar larvae of B. mori was assessed using Cya LC5, LC10 and LC20, as well as a starvation treatment group for comparison. Short-term exposure (24 h) to different concentrations of Cya resulted in delayed development of silk glands in B. mori. Meanwhile, the body weight, silk gland weight, silk gland index and cocoon quality were significantly reduced in a concentration-dependent manner, except for the Cya LC5 treatment. Histopathological and ultrastructural analysis revealed that Cya LC10 induced disruption of the nuclear membrane and endoplasmic reticulum in the posterior silk gland (PSG) cells, leading to the formation of intracellular vacuoles. Transcriptome sequencing of PSGs identified 2152 genes that were differentially expressed after exposure to Cya LC10, with 1153 down-regulated genes and 999 up-regulated genes. All differentially expressed genes were subjected to functional annotation using gene ontology and Kyoto encyclopedia of genes and genomes database, and it was found that protein synthesis-related pathways were significantly enriched, with the majority of genes being down-regulated. Furthermore, the transcription levels of genes involved in "protein processing in endoplasmic reticulum", "protein export", "proteasome" and "DNA replication" were quantified using qRT-PCR. Our findings suggested that short-term exposure to Cya LC10 resulted in disruption of DNA replication, as well as protein transport, processing and hydrolysis in the PSG cells of B. mori. The results of this study provide a theoretical foundation for the safe utilization of Cya in sericulture production.

Intramembrane client recognition potentiates the chaperone functions of calnexin

One-third of the human proteome is comprised of membrane proteins, which are particularly vulnerable to misfolding and often require folding assistance by molecular chaperones. Calnexin (CNX), which engages client proteins via its sugar-binding lectin domain, is one of the most abundant ER chaperones, and plays an important role in membrane protein biogenesis. Based on mass spectrometric analyses, we here show that calnexin interacts with a large number of nonglycosylated membrane proteins, indicative of additional nonlectin binding modes. We find that calnexin preferentially bind misfolded membrane proteins and that it uses its single transmembrane domain (TMD) for client recognition. Combining experimental and computational approaches, we systematically dissect signatures for intramembrane client recognition by calnexin, and identify sequence motifs within the calnexin TMD region that mediate client binding. Building on this, we show that intramembrane client binding potentiates the chaperone functions of calnexin. Together, these data reveal a widespread role of calnexin client recognition in the lipid bilayer, which synergizes with its established lectin-based substrate binding. Molecular chaperones thus can combine different interaction modes to support the biogenesis of the diverse eukaryotic membrane proteome.