Abstract
Rotavirus is the leading agent causing acute gastroenteritis in young children, with the P[8] genotype accounting for more than 80% of infections in humans. The molecular bases for binding of the VP8* domain from P[8] VP4 spike protein to its cellular receptor, the secretory H type-1 antigen (Fuc-α1,2-Gal-β1,3-GlcNAc; H1), and to its precursor lacto-N-biose (Gal-β1,3-GlcNAc; LNB) have been determined. The resolution of P[8] VP8* crystal structures in complex with H1 antigen and LNB and site-directed mutagenesis experiments revealed that both glycans bind to the P[8] VP8* protein through a binding pocket shared with other members of the P[II] genogroup (i.e.: P[4], P[6] and P[19]). Our results show that the L-fucose moiety from H1 only displays indirect contacts with P[8] VP8*. However, the induced conformational changes in the LNB moiety increase the ligand affinity by two-fold, as measured by surface plasmon resonance (SPR), providing a molecular explanation for the different susceptibility to rotavirus infection between secretor and non-secretor individuals. The unexpected interaction of P[8] VP8* with LNB, a building block of type-1 human milk oligosaccharides, resulted in inhibition of rotavirus infection, highlighting the role and possible application of this disaccharide as an antiviral. While key amino acids in the H1/LNB binding pocket were highly conserved in members of the P[II] genogroup, differences were found in ligand affinities among distinct P[8] genetic lineages. The variation in affinities were explained by subtle structural differences induced by amino acid changes in the vicinity of the binding pocket, providing a fine-tuning mechanism for glycan binding in P[8] rotavirus.
Highlights
Rotaviruses are the leading etiologic agent of viral gastroenteritis in infants and young children worldwide and are responsible for an estimated 140,000 deaths each year in developing countries [1]
VP8 from P[8] genotype recognize the H type-1 (H1) antigen precursor lacto-N-biose (Gal-β1,3-GlcNAc, Lewisc, LNB; S2 Fig) but differences in the binding abilities were found among different genetic lineages and strains
The results showed that both proteins were able to bind H1 and LNB, binding to the first antigen was higher
Summary
Rotaviruses are the leading etiologic agent of viral gastroenteritis in infants and young children worldwide and are responsible for an estimated 140,000 deaths each year in developing countries [1]. The typical classification of rotaviruses was derived from their genome composition and the immunological reactivity of three of their structural proteins: VP6, VP7 and VP4. Rotaviruses are classified into at least 7 groups (A to G) according to the immunological reactivity of the VP6 middle layer protein, with group A rotavirus being the most commonly associated with infections in human. The two outer capsid proteins VP7 and VP4, elicit neutralizing antibodies that can induce viral protection. Using these two proteins, a traditional dual classification system of group A rotaviruses into G (depending on the VP7 glycoprotein) and P (depending on the protease-sensitive VP4) types was established [2]. Viruses carrying G1[P8], G2[P4], G3[P8] and G4[P8] represent over 90% of human rotaviruses strains co-circulating in most countries [2], with the P[8] genotype, which comprises four different genetic lineages (I to IV [4]), being relevant [5]
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