Abstract:
Viruses are a global threat, causing a large variety of diseases and numerous deaths.
Individual viral strains have the ability to emerge rapidly and adapt to the host, hence
there is a constant danger, sometimes more in the background of public interest, and
sometimes, as at present, more visible. Detailed knowledge about viral spread and
proliferation is still limited and as a consequence, research efforts are continuously
increasing to tackle this shortage. The attachment of a virus particle to the host cell
is the first and as such crucial step during viral replication. Structural biology analysis of
the interaction between host cell receptors and viral proteins provides not only a better
understanding of the viral tropism, but also possible targets to interfere.
Human adenoviruses (HAdVs) are a wide-spread species of double-stranded DNA
viruses that can cause infections in various areas of the body. Depending on the virus
type, they bind via the fiber knob (FK) domain to various attachment receptors, for
example sialic acid-containing glycans or surface proteins such as CAR or CD46.
One of several HAdVs covered in this thesis is type 56 (HAdV56), which has a low
seroprevalence among humans and was shown to require CD46 binding for subsequent
infection. Using X-ray crystallography, the atomic structure of the HAdV56 FK was
determined and a binding site for sialic acid was confirmed. However, binding of CD46
in comparison to established CD46-binding HAdVs at the respective position is excluded
due to significant structural differences, indicating an alternative binding mechanism.
HAdV37 is a cause of epidemic keratoconjunctivitis, a severe infection of the eye.
The attachment to the host cell is mediated by sialic acid and can be blocked by trivalent,
sialic acid-based inhibitors. In this work, a new generation of inhibitor molecules was,
for the first time, fully resolved by X-ray crystallography in complex with the HAdV37
FK. Additionally, binding was confirmed to HAdV26 in structural studies and an adapted
version of the inhibitor molecule was shown to bind HAdV36, which expands the
potential target range for a medical application.
Orthoreoviruses (ReoVs) are double-stranded RNA viruses that are mostly harmless
for humans, but can lead to severe diseases and death in mice. Apart from being
a model subject, ReoVs are studied for the targeted treatment of cancer cells. The
detailed understanding of the virus-host cell interaction is essential for developing such
therapeutics. Recently, the human Nogo receptor-1 (NgR1) was discovered as an
additional attachment factor for ReoVs. In contrast to the well-established receptors
sialic acid and JAM-A, NgR1 is not binding to the σ1 spike protein, but to the outer
capsid protein σ3. Using cryogenic electron microscopy (cryoEM) analysis, the inter-
action of an intact virion liganded with NgR1 was structurally characterized. A novel
binding mode of one NgR1 protomer in a canyon in between two σ3s was confirmed
and two unique interaction areas were identified. This low-affinity but high-avidity bin-
ding of a neural receptor with a non-primary attachment capsomer is unique among yet
described virus-host interactions and will greatly enhance the understanding of ReoV
pathogenesis.
In summary, this work provides novel findings to better understand the host cell
attachment of adenoviruses and reoviruses. This will contribute to developing strategies
for preventing viral infections and exploiting viruses for therapeutic applications.
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