Functional and epidemiological data suggest that N -linked glycans on the SARS-CoV-2 Spike protein may contribute to viral infectivity. To investigate this, we created a panel of N-to-Q mutations at N -glycosylation sites proximal to the Spike S1-S2 (N61, N603, N657, and N616) and S2′ (N603 and N801) proteolysis sites. Some of these mutations, particularly N61Q and N801Q, reduced Spike incorporation into Spike-pseudotyped lentivirus and authentic SARS-CoV-2 virus-like particles (VLPs). These mutations also reduced pseudovirus and VLP entry into ACE2-expressing cells by 80 to 90%. In contrast, glycan mutations had a relatively minor effect on cell surface expression of Spike, ACE2 binding, and syncytia formation. A similar dichotomy in function was observed when virus was produced in host cells lacking ER chaperones, calnexin and calreticulin. Here, while both chaperones regulated pseudovirus function, only VLPs produced in calnexin KOs were less infectious. Overall, Spike N -glycans are likely critical for SARS-CoV-2 function and could serve as drug targets for COVID-19.

Nitroxyl (HNO) is a gaseous molecule with unique pharmacological functions distinct from those of nitric oxide. Because HNO is highly reactive with biological molecules, spatiotemporally controllable HNO releasers are required. Herein, we report the first visible-light-controllable HNO releasers, based on caged Piloty's acid, and we demonstrate their applicability in living cells.

Glycans have been shown to play a key role in many biological processes, such as signal transduction, immunogenicity, and disease progression. Among the various glycosylation modifications found on cell surfaces and in biomolecules, sialylation is especially important, because sialic acids are typically found at the terminus of glycans and have unique negatively charged moieties associated with cellular and molecular interactions. Sialic acids are also crucial for glycosylated biopharmaceutics, where they promote stability and activity. In this regard, heterogenous sialylation may produce variability in efficacy and limit therapeutic applications. Homogenous sialylation may be achieved through cellular and molecular engineering, both of which have gained traction in recent years. In this paper, we describe the engineering of intracellular glycosylation pathways through targeted disruption and the introduction of carbohydrate active enzyme genes. The focus of this review is on sialic acid-related genes and efforts to achieve homogenous, humanlike sialylation in model hosts. We also discuss the molecular engineering of sialyltransferases and their application in chemoenzymatic sialylation and sialic acid visualization on cell surfaces. The integration of these complementary engineering strategies will be useful for glycoscience to explore the biological significance of sialic acids on cell surfaces as well as the future development of advanced biopharmaceuticals.