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Virus attachment at the cell surface often involves the establishment of multiple ligand-receptor interactions between viral capsid proteins and glycans in the glycocalyx. Multivalency likely contributes to strengthening and fine-tuning virus dynamics at the cell surface to optimize entry. Here, we present experimental and theoretical frameworks to describe how virus attachment, detachment, and diffusion at the cell surface are modulated by multivalency. We focus on human papillomavirus 16 (HPV16), a leading cause of cervical cancer and its multivalent interactions with heparan sulfate (HS), a ubiquitous cell-surface glycan. Using single-particle tracking microscopy, we investigate the dynamic behavior of HPV16 particles interacting with multiple HS chains through a glycocalyx mimic consisting of end-tethered heparin chains that were selectively desulfated. We further establish a theoretical framework to predict the dynamic behavior of individual virus particles interacting with multiple cellular receptors and apply it to the HPV16-HS binding system using previously published association and dissociation rates of the individual capsomer-glycan bonds. Our experiments reveal that N-sulfation is essential to ensure HPV16 association and validate our theoretical prediction that at biologically relevant timescales, the lifetime of monovalent interaction primarily influences the apparent particle attachment behavior. Conversely, the nature of the sulfate group had a marginal effect on particle dissociation in the experiments, due to the great influence of multivalency on the particle’s interaction lifetime. Experiments and simulations also indicate that the mobility of HPV16 particles on heparin surfaces is highly restricted due to the relatively high affinity of the monovalent interactions, suggesting that particle motion due to the creation and rupturing of individual bonds is unlikely key in HPV16 recruitment. Together, these findings provide quantitative mechanistic insights into how virus-glycan interactions are modulated. They highlight the importance of HS chemistry in modulating early HPV16 engagement and suggest new targets against viral binding.

Human apolipoprotein E (ApoE) has been shown to play important roles during primary infection and pathogenesis of several viruses. Furthermore, epidemiological studies suggest that interactions between ApoE 4 and herpes simplex virus type-1 (HSV1) could associate with higher risk of Alzheimer’s disease. Nevertheless, little is known about the ApoE-HSV1 interactions at molecular levels. Here, we investigate the effects of ApoE on HSV1 infection in vitro. Our results show that ApoE promotes HSV1 growth, which is attributed to the incorporation of ApoE into HSV1 particles. Using both biological and biophysical approaches, we conclude that ApoE-coated HSV1 demonstrates a more efficient attachment to and faster release from the cell surface. Mechanistic studies reveal that ApoE modifies HSV1 interactions with heparan sulfate, thereby modulating interactions between HSV1 and the cell surface. Overall, our results provide new insights into the roles of ApoE during HSV1 infections which may inspire future studies on Alzheimer’s disease etiology.

The spread of SARS-CoV-2 led to the emergence of several variants of concern (VOCs). The spike glycoprotein, responsible for engaging the viral receptor, exhibits the highest density of mutations, suggesting an ongoing evolution to optimize viral entry. This study characterizes the bond formed by virion mimics carrying the SARS-CoV-2 spike protein and the plasma membrane of host cells in the early stages of virus entry. Contrary to the traditional analysis of isolated ligand-receptor pairs, we utilized well-defined biomimetic models and biochemical and biophysical techniques to characterize the multivalent interaction of VOCs with the complex cell membrane. We observed an overall increase in the binding affinity for newer VOCs. By progressively reducing the system complexity, we identify heparan sulfate (HS) as a main driver of this variation, with a 10-fold increase in affinity for Omicron BA.1 over that of the original strain. These results demonstrate the essential role of coreceptors, particularly HS, in the modulation of SARS-CoV-2 infection and highlight the importance of multiscale biophysical and biochemical assays that account for membrane complexity to fully characterize and understand the role of molecular components and their synergy in viral attachment and entry.

Enteric adenovirus types F40 and 41 (EAdVs) are a leading cause of diarrhea and diarrhea-associated death in young children and have recently been proposed to cause acute hepatitis in children. EAdVs have a unique capsid architecture and exhibit — unlike other human adenoviruses — a relatively strict tropism for gastrointestinal tissues with, to date, understudied infection mechanism and unknown target cells. In this study, we turn to potentially limiting host factors by comparing EAdV entry in cell lines with respiratory and intestinal origin by cellular perturbation, virus particle tracking, and transmission electron microscopy. Our analyses highlight kinetic advantages for EAdVs in duodenal HuTu80 cell infection and reveal a larger fraction of mobile particles, faster virus uptake, and infectious particle entry in intestinal cells. Moreover, EAdVs display a dependence on clathrin- and dynamin-dependent pathways in intestinal cells. Detailed knowledge of virus entry routes and host factor requirements is essential to understanding pathogenesis and developing new countermeasures. Hence, this study provides novel insights into the entry mechanisms of a medically important virus with emerging tropism in a cell line originating from a relevant tissue. IMPORTANCE Enteric adenoviruses have historically been difficult to grow in cell culture, which has resulted in lack of knowledge of host factors and pathways required for infection of these medically relevant viruses. Previous studies in non-intestinal cell lines showed slow infection kinetics and generated comparatively low virus yields compared to other adenovirus types. We suggest duodenum-derived HuTu80 cells as a superior cell line for studies to complement efforts using complex intestinal tissue models. We show that viral host cell factors required for virus entry differ between cell lines from distinct origins and demonstrate the importance of clathrin-mediated endocytosis.