Seminar

NMR Experiments Reveal Allosteric Control of Carbohydrate Recognition of Noroviruses

Alvaro Mallagaray, PhD

The first steps of a Norovirus (NoV) infection require specific interactions with carbohydrate epitopes of the host. In the case of human NoV these carbohydrate epitopes are histo blood group antigens (HBGAs). Depending on the genogroup and on the genotype of the virus different specificities are observed for e.g. blood group A or B.[1] We have been studying genogroup II (GII) NoVs and their interactions with HBGAs using functional carbohydrate binding domains, so-called P-dimers, of the viral coat protein as well as virus like particles (VLPs).[2,3] Our studies have shown that the binding mechanism is more complex than a simple one-site binding process. Binding of HBGAs to P-dimers, or to VLPs is characterized by discontinuities in binding isotherms derived from STD NMR experiments or from chemical shift perturbation experiments using uniformly 2H,15N-labeled P-dimers. In order to quantitate the underlying cooperativity, we have fitted extended Hill-equations to the experimental binding curves yielding apparent dissociation constants for each step. As this does not reveal the mechanism behind the recognition process we are now working on a backbone assignment of a 70 kDa P-dimer of a predominant (GII.4 Saga) NoV strain. So far, we have assigned ca. 50% of all resonances giving us first insights into possible allosteric pathways in the protein. Here, we will report on these results and their possible biological implications.