Glycostructures in Virus-Host Recognition Processes

The attachment of viruses to hosts usually involves specific interactions of viral coat proteins with host cell receptors. In a couple of key experiments we showed that STD NMR is ideally suited to map the binding of low molecular weight ligands to native human rhinoviruses (HRV-2) at atomic resolution. From STD NMR we obtained the binding epitopes and relative dissociation constants for synthetic entry inhibitors that bind into the canyon binding site of the virus demonstrating that this novel technique provides a direct route to the rational design of entry inhibitors against viral infections. The approach is now extended to investigate the binding of fragments of the human LDL and VLDL receptors to HRV-2, and thus to map the viral entry process at a molecular level. First experiments have shown that it is possible to use STD NMR to resolve the binding epitope of VLDL receptor fragments at atomic resolution. This work is underway and will pave the way for a fast characterization of binding properties of different virus serotypes to the human LDL and VLDL receptors at atomic resolution.

These experiments are a proof of principle, and therefore we have applied this approach to other viruses. At the present, Norovirus infections are in the focus of our interest. To date, only very few entry inhibitors against viral infections have been identified. On the other hand, the availability of such compounds would offer a variety of novel therapeutic strategies to combat viral infections. As an example we have chosen Noroviruses that belong to the family of Caliciviridae. Noroviruses are non-enveloped positive stranded RNA viruses that bind to histo-blood group antigens (HBGAs) on the surface of host cells. Noroviruses are subdivided into two genogroups I and II and are extremely contagious, i.e. only 10 to 100 virions are sufficient to infect a person. Therefore, infections are usually epidemic and have been declared as B-agents by the NIH/CDC bidodefense program. There are no known cures, and vaccination strategies are not within sight. Our goal is to understand the structural and dynamic constraints of the virus-host recognition process as a basis for the rapid micro-evolution of the virus, and to finally design potent entry-inhibitors against Norovirus infections. So far, we have successfully determined the binding epitopes of several natural receptor molecules (so called human histo-blood group antigens, HBGAs) as shown in the example in Fig. 2. With so called interligand NOEs we have identified other binding fragments from so called fragment libraries. Using a novel design concept we have already synthesized an entry inhibitor with nanomolar affinity (collaboration with Prof. Bundle, Alberta Ingenuity Centre for Carbohydrate Sciences, Edmonton, Alberta, Canada).