- Volume 106, Issue 5, 2025

Human immunodeficiency virus type-1 (HIV-1) can infect non-dividing cells by passing through the selective permeability barrier of the nuclear pore complex. The viral capsid is essential for successfully delivering the HIV-1 genome into the nucleus. Nucleoporin 153 (NUP153) interacts with the HIV-1 capsid via a C-terminal capsid-binding motif (hereafter named CbM.1) to licence HIV-1 nuclear ingress. Deletion or mutation of CbM.1 in NUP153 causes a reduction in capsid interaction but does not prevent HIV-1 nuclear ingress or completely block capsid interaction. This paper combines molecular modelling with biochemical and HIV infection assays to identify capsid-binding motif 2 (CbM.2) in the C-terminus of NUP153 that is similar in sequence to CbM.1. CbM.2 has an FG dipeptide motif predicted to interact with a hydrophobic pocket in capsid protein (CA) hexamers similar to CbM.1. CA hexamers can interact with CbM.2, and the deletion of both CbM.1 and CbM.2 results in a lower capsid interaction than a single CbM.1 deletion. The loss of CbM.1 is complemented by CbM.2, an interaction dependent on the FG motif. In the context of the nuclear pore complex, a loss-of-function mutation in CbM.1 reduces HIV nuclear ingress as measured by transduction and 2-LTR circles, whereas the mutation of CbM.2 causes a large increase in 2-LTR circles. Our results highlighted a previously unidentified FG dipeptide-containing motif (CbM.2) in NUP153 that binds the HIV-1 capsid at the common hydrophobic pocket on CA hexamers.

The silkworm, Bombyx mori, is a crucial model insect in agriculture and biological research. Tetraspanins, known for their effects in regulating cellular functions like cell signalling, adhesion, migration and diffusion, take on a crucial role in viral dynamics, influencing both viral spread and entry into host cells. In this study, a tetraspanin gene called BmTsp.C from the silkworm genome was identified and investigated. Tissue profiles showed that BmTsp.C has the highest transcription level in midgut, with a marked increase following viral infection. The immunofluorescence localization suggested that BmTsp.C is primarily distributed on the cell membrane. Additionally, overexpression of BmTsp.C in BmN cells facilitated the proliferation of BmNPV. Meanwhile, siRNA-mediated knockdown of BmTsp.C could inhibit viral proliferation. In addition, knockdown of BmTsp.C at the individual level further validated the remarkable effect of BmTsp.C during viral infestation. Furthermore, overexpression of BmTsp.C could regulate the expression of apoptosis-related genes. Results from flow cytometry indicated a decrease in the number of apoptotic cells after overexpression of BmTsp.C. Taken together, our results demonstrated that BmTsp.C, as an important factor in the Tetraspanin-enriched microdomains, exerts a significant influence on the proliferation of BmNPV, most likely through the cellular apoptosis pathway.

Aegerolysins are lipid-binding proteins associated with multiple functions, including membrane pore-formation, insecticidal toxicity and defence against predators. Whilst distributed over the kingdoms of the Tree of Life, ascoviruses are the only representative viruses that encode an aegerolysin-like protein. Ascoviruses are entomopathogenic and possess a large dsDNA genome. The present study aimed to functionally characterize the aegerolysin-like protein of Heliothis virescens ascovirus 3h (HvAV-3h), encoded by ORF85, and to explore its potential roles in the interaction between the ascovirus and its host. Our results demonstrate the importance of this species-specific protein to HvAV-3h replication in host cells. In vivo, silencing of this gene for 12–72 h significantly increased the expression of some innate immunity-associated genes, including Toll (114-fold), IMD (44.7-fold) and Hopscotch (22.9-fold). In parallel, we detected significant gradual increases in MyD88 and Relish and decreases in PIAS. Moreover, histopathological analyses of infected larval tissues indicated reduced tissue damage after 72 h of ORF85 gene silencing. The prokaryotic expression of the HvAV-3h aegerolysin, followed by feeding to third-instar Spodoptera exigua larvae for 24 or 48 h led to significant reductions in larval weight. Moreover, the in vitro treatment demonstrated a bactericidal action against Lysinibacillus xylanilyticus, a bacterial resident of some insect guts. Overall, our findings suggest that the protein encoded by ORF85 is associated with the pathogenicity of HvAV-3h and its ability to replicate in host cells. Additionally, aegerolysin may inhibit or kill specific bacterial species in the host microbiome during infection, potentially modulating the host immune response.