TMPRSS2 and glycan receptors synergistically facilitate coronavirus entry.

The entry of coronaviruses is initiated by spike recognition of host cellular receptors, involving proteinaceous and/or glycan receptors. Recently, TMPRSS2 was identified as the proteinaceous receptor for HCoV-HKU1 alongside sialoglycan as a glycan receptor. However, the underlying mechanisms for viral entry remain unknown. Here, we investigated the HCoV-HKU1C spike in the inactive, glycan-activated, and functionally anchored states, revealing that sialoglycan binding induces a conformational change of the NTD and promotes the neighboring RBD of the spike to open for TMPRSS2 recognition, exhibiting a synergistic mechanism for the entry of HCoV-HKU1. The RBD of HCoV-HKU1 features an insertion subdomain that recognizes TMPRSS2 through three previously undiscovered interfaces. Furthermore, structural investigation of HCoV-HKU1A in combination with mutagenesis and binding assays confirms a conserved receptor recognition pattern adopted by HCoV-HKU1. These studies advance our understanding of the complex viral-host interactions during entry, laying the groundwork for developing new therapeutics against coronavirus-associated diseases.

Structural insight of cell surface sugars in viral infection and human milk glycans as natural antiviral substance.

Viral infections are caused by the adhesion of viruses to host cell receptors, including sialylated glycans, glycosaminoglycans, and human blood group antigens (HBGAs). Atomic-level structural information on the interactions between viral particles or proteins with glycans can be determined to provide precise targets for designing antiviral drugs. Milk glycans, existing as free oligosaccharides or glycoconjugates, have attracted increasing attention; milk glycans protect infants against infectious diseases, particularly poorly manageable viral infections. Furthermore, several glycans containing structurally distinct sialic acid/fucose/sulfate modifications in human milk acting as a "receptor decoy" and serving as the natural antiviral library, could interrupt virus-receptor interaction in the first line of defense for viral infection. This review highlights the basis of virus-glycan interactions, presents specific glycan receptor binding by gastroenterovirus viruses, including norovirus, enteroviruses, and the breakthroughs in the studies on the antiviral properties of human milk glycans, and also elucidates the role of glycans in respiratory viruses infection. In addition, recent advances in methods for performing virus/viral protein-glycan interactions were reported. Finally, we discuss the prospects and challenges of the studies on the clinical application of human milk glycan for viral interventions.

In Vivo Cancer Microenvironment Responsive Glycan Receptor-Targeted Nanoparticles for Gemcitabine Delivery to Benzo[a]pyrene-Induced Lung Cancer Model.

Targeted gemcitabine (GEB) loaded 5-N-acetyl-neuraminic acid (Neu5Ac) assembled chitosan nanoparticles (CA-NPs) were formulated by ionotropic gelation process and evaluated for physicochemical and morphological characterization, in vitro and in vivo studies in A-549 cells and lung cancer mice model, respectively. The mean diameter of GEB-CA-Neu5Ac-NPs determined by dynamic light scattering was 161.16 ± 7.70 nm with a polydispersity index (PDI) value of 0.303 ± 0.011 and its zeta potential and entrapment efficiency (%EE) were 40.3 ± 3.45 mv and 66.11 ± 1.94%, respectively. The in vitro cellular uptake studies showed that glycan receptor-targeted nanoparticles deliver significantly more amount (p < 0.001) of GEB into the A-549 lung cancerous cells than non-targeted nanoparticles. The cytotoxicity study using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay clearly demonstrated that GEB-CA-Neu5Ac-NPs have lower IC50 value (6.39 ± 3.78 µg/ml) than others groups that showed that the greater lung cancerous cells inhibition potential of targeted nanoparticles. The in vivo biodistribution of the GEB-loaded 5-N-acetyl-neuraminic acid conjugated chitosan nanoparticles was revealed that targeted nanoparticles showed higher accumulation and retention for an extended period of time due to the active targeting ability of Neu5Ac to glycan receptors. Histopathological examination showed significant recovery in the physiological architecture upon administration of targeted nanoparticles. The glycan receptor-targeted nanoparticles treated groups showed a significant decline in the number of metastatic lung epithelial cells, as compared to the untreated positive control group (p < 0.001) confirming higher anticancer efficacy of the GEB-CA-Neu5Ac-NPs.