ABSTRACT
Human adenoviruses are phylogenetically divided across seven species, A-G, causing transient mild illnesses, except in immunocompromised individuals. Their double stranded DNA genome is amenable to genetic manipulations, enabling development of highly engineered virotherapies. Species D adenoviruses have naturally low seroprevalence rates, an important trait in avoiding neutralising anti-vector immunity. We previously demonstrated that HAdV-D26, the platform of the Janssen SARS-CoV2 vaccine, uses sialic acid as a primary cell entry receptor. Here, we structurally and biologically investigated sialic acid usage across species D. We solved multiple structures of species D adenovirus fiber knob proteins alone and in complex with sialic acid, identifying a conserved binding pocket common with known sialic acid binders HAdV-D26 and 37. Using fiber-knob pseudotyped viruses, we demonstrate significantly reduced transduction in cells treated with neuraminidase to remove sialic acid residues in HAdV-D26 and 53, with HAdV-D15, 24 and 29 also demonstrating non-significant reductions. IC50 data also showed highlighted binding to CAR, although at a significantly lower affinity compared to the CAR-binding HAdV-C5. Improved understanding of the usage of sialic acid as a receptor will enable better exploitation of the species D adenoviruses as therapeutic vectors. Our findings raise the possibility of a conserved sialic acid binding pocket within species D adenoviruses resulting in varying affinity levels. Further evaluation of specific glycan binding patterns used by these viruses, as observed between HAdV-D37 and GD1a glycan, will better inform the design of appropriate antivirals to contain adenovirus outbreaks as well as the engineering of targeted vectors for translational applications.