Cloning, expression, purification, crystallization and preliminary X-ray diffraction analysis of the VP8* carbohydrate-binding protein of the human rotavirus strain Wa

Bivalent rotavirus VP4∗ stimulates protective antibodies against common genotypes of human rotaviruses

Non-replicating rotavirus vaccines are an alternative strategy to improve the efficacy and safety of rotavirus vaccines. The spike protein VP4, which could be enzymatically cleaved into VP8∗ and VP5∗, is an ideal target for the development of recombinant rotavirus vaccine. In our previous studies, we demonstrated that the truncated VP4 (aa26-476, VP4∗) could be a more viable vaccine candidate compared to VP8∗ and VP5∗. Here, to develop a human rotavirus vaccine, the VP4∗ proteins of P[4], P[6], and P[8] genotype rotaviruses were expressed. All VP4∗ proteins can stimulate high levels of neutralizing antibodies in both guinea pigs and rabbits when formulated in aluminum adjuvant. Furthermore, bivalent VP4∗-based vaccine (P[8] + P[6]-VP4∗) can stimulate high levels of neutralizing antibodies against various genotypes of rotavirus with no significant difference as compared to the trivalent vaccines. Therefore, bivalent VP4∗ has the potential to be a viable rotavirus vaccine candidate for further development.

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Purified rotavirus VP4∗ proteins form homogenic and stable trimers

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VP4∗ stimulated high levels of homotypic and heterotypic neutralizing antibodies

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The immunogenicity of different genotype VP4∗ is not influenced by each other

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Bivalent VP4∗ (P[8]+P[6]) stimulated protective immunity against most prevalent rotaviruses

Crystallization of a nonreplicating rotavirus vaccine candidate

Nonreplicating rotavirus vaccine (NRRV) candidates are being developed with the aim of serving the needs of developing countries. A significant proportion of the cost of manufacturing such vaccines is the purification in multiple chromatography steps. Crystallization has the potential to reduce purification costs and provide new product storage modality, improved operational flexibility, and reduced facility footprints. This communication describes a systematic approach for the design of the crystallization of an NRRV candidate, VP8 subunit proteins fused to the P2 epitope of tetanus toxin, using first‐principles models and preliminary experimental data. The first‐principles models are applied to literature data to obtain feasible crystallization conditions and lower bounds for nucleation and growth rates. Crystallization is then performed in a hanging‐drop vapor diffusion system, resulting in the nucleation and growth of NRRV crystals. The crystals obtained in a scaled‐up evaporative crystallization contain proteins truncated in the P2 region, but have no significant differences with the original samples in terms of antibody binding and overall conformational stability. These results demonstrate the promise of evaporative crystallization of the NRRV.

Relative roles of GM1 ganglioside, N-acylneuraminic acids, and α2β1 integrin in mediating rotavirus infection

N-acetyl- and N-glycolylneuraminic acids (Sia) and α2β1 integrin are frequently used by rotaviruses as cellular receptors through recognition by virion spike protein VP4. The VP4 subunit VP8*, derived from Wa rotavirus, binds the internal N-acetylneuraminic acid on ganglioside GM1. Wa infection is increased by enhanced internal Sia access following terminal Sia removal from main glycan chains with sialidase. The GM1 ligand cholera toxin B (CTB) reduces Wa infectivity. Here, we found sialidase treatment increased cellular GM1 availability and the infectivity of several other human (including RV-3) and animal rotaviruses, typically rendering them susceptible to methyl α-d-N-acetylneuraminide treatment, but did not alter α2β1 usage. CTB reduced the infectivity of these viruses. Aceramido-GM1 inhibited Wa and RV-3 infectivity in untreated and sialidase-treated cells, and GM1 supplementation increased their infectivity, demonstrating the importance of GM1 for infection. Wa recognition of α2β1 and internal Sia were at least partially independent. Rotavirus usage of GM1 was mapped to VP4 using virus reassortants, and RV-3 VP8* bound aceramido-GM1 by saturation transfer difference nuclear magnetic resonance (STD NMR). Most rotaviruses recognizing terminal Sia did not use GM1, including RRV. RRV VP8* interacted minimally with aceramido-GM1 by STD NMR. Unusually, TFR-41 rotavirus infectivity depended upon terminal Sia and GM1. Competition of CTB, Sia, and/or aceramido-GM1 with cell binding by VP8* from representative rotaviruses showed that rotavirus Sia and GM1 preferences resulted from VP8*-cell binding. Our major finding is that infection by human rotaviruses of commonly occurring VP4 serotypes involves VP8* binding to cell surface GM1 glycan, typically including the internal N-acetylneuraminic acid.

IMPORTANCE

Rotaviruses, the major cause of severe infantile gastroenteritis, recognize cell surface receptors through virus spike protein VP4. Several animal rotaviruses are known to bind sialic acids at the termini of main carbohydrate chains. Conversely, only a single human rotavirus is known to bind sialic acid. Interestingly, VP4 of this rotavirus bound to sialic acid that forms a branch on the main carbohydrate chain of the GM1 ganglioside. Here, we use several techniques to demonstrate that other human rotaviruses exhibit similar GM1 usage properties. Furthermore, binding by VP4 to cell surface GM1, involving branched sialic acid recognition, is shown to facilitate infection. In contrast, most animal rotaviruses that bind terminal sialic acids did not utilize GM1 for VP4 cell binding or infection. These studies support a significant role for GM1 in mediating host cell invasion by human rotaviruses.

Construction and characterization of human rotavirus recombinant VP8* subunit parenteral vaccine candidates

Two currently licensed live oral rotavirus vaccines (Rotarix® and RotaTeq®) are highly efficacious against severe rotavirus diarrhea. However, the efficacy of such vaccines in selected low-income African and Asian countries is much lower than that in middle or high-income countries. Additionally, these two vaccines have recently been associated with rare case of intussusception in vaccinated infants. We developed a novel recombinant subunit parenteral rotavirus vaccine which may be more effective in low-income countries and also avert the potential problem of intussusception. Truncated recombinant VP8* (ΔVP8*) protein of human rotavirus strain Wa P[8], DS-1 P[4] or 1076 P[6] expressed in Escherichia coli was highly soluble and was generated in high yield. Guinea pigs hyperimmunized intramuscularly with each of the ΔVP8* proteins (i.e., P[8], P[4] or P[6]) developed high levels of homotypic as well as variable levels of heterotypic neutralizing antibodies. Moreover, the selected ΔVP8* proteins when administered to mice at a clinically relevant dosage, route and schedule, elicited high levels of serum anti-VP8* IgG and/or neutralizing antibodies. Our data indicated that the ΔVP8* proteins may be a plausible additional candidate as new parenteral rotavirus vaccines.

Towards achieving a high-resolution structure of rotavirus particles

Evaluation of: Aoki ST, Settembre EC, Trask SD, Greenberg HB, Harrison SC, Dormitzer PR: Structure of rotavirus outer-layer protein VP7 bound with a neutralizing Fab. Science 324 (5993), 1444–1447 (2009). The determination of the molecular structure of the trimer of VP7, one of the outer layer proteins of rotaviruses, has significantly contributed to the knowledge of the overall structure of rotavirus particles. The molecular mechanism of rotavirus neutralization has been clarified and a topological explanation been found for the emergence of antibody escape mutants. Furthermore, translational work was enabled by engineering VP7 mutants, which form stable trimers by means of novel disulfide bridges linking the different subunits together; such a construct could become an attractive and safe vaccine candidate.

Disease-associated carbohydrate-recognising proteins and structure-based inhibitor design

The role of carbohydrate-related pathways in a wide range of clinically significant diseases has provided great impetus for researchers to characterise key proteins as targets for drug discovery. Carbohydrate-recognising proteins essential in the lifecycles of high health impact pathogens and diseases such as diabetes, cancer, autoimmunity, inflammation and in-born errors of metabolism continue to stimulate much interest in both structure elucidation and structure-based drug design. For example, advances in structure-based inhibitor design against the mycobacterial enzyme UDP-galactopyranose mutase offer new hope in next generation anti-tuberculosis chemotherapeutics. The appearance of H5N1 avian influenza virus has re-stimulated much research on influenza virus haemagglutinin and sialidase. These latest developments on influenza virus sialidase have provided new opportunity for the development of Group 1-specific anti-influenza drugs. The role of siglecs and galectins in a range of disease processes such as inflammation, apoptosis and cancer progression has also inspired significant structure-based inhibitor design research.

Crystallization and preliminary X-ray diffraction analysis of the carbohydrate-recognizing domain (VP8*) of bovine rotavirus strain NCDV

The infectivity of rotavirus is dramatically enhanced by proteolytic cleavage of its outer layer VP4 spike protein into two functional domains, VP8* and VP5*. The carbohydrate-recognizing domain VP8* is proposed to bind sialic acid-containing host cell-surface glycans and this is followed by a series of subsequent virus-cell interactions. Live attenuated human and bovine rotavirus vaccine candidates for the prevention of gastroenteritis have been derived from bovine rotavirus strain NCDV. The NCDV VP8*(64-224) was overexpressed, purified to homogeneity and crystallized in the presence of an N-acetylneuraminic acid derivative. X-ray diffraction data were collected to a resolution of 2.0 A and the crystallographic structure of NCDV VP8*(64-224) was determined by molecular replacement.

Expression, purification, crystallization and preliminary X-ray diffraction analysis of the VP8* sialic acid-binding domain of porcine rotavirus strain OSU

The rotavirus outer capsid spike protein VP4 is utilized in the process of rotavirus attachment to and membrane penetration of host cells. VP4 is cleaved by trypsin into two domains: VP8* and VP5*. The VP8* domain is implicated in initial interaction with sialic acid-containing cell-surface carbohydrates and triggers subsequent virus invasion. The VP8* domain from porcine OSU rotavirus was cloned and expressed in Escherichia coli. Different crystal forms (orthorhombic P2(1)2(1)2(1) and tetragonal P4(1)2(1)2) were harvested from two distinct crystallization conditions. Diffraction data have been collected to 2.65 and 2.2 A resolution and the VP8*(65-224) structure was determined by molecular replacement.

Insight into host cell carbohydrate-recognition by human and porcine rotavirus from crystal structures of the virion spike associated carbohydrate-binding domain (VP8*)

Rotavirus infection leads to the death of half a million children annually. The exact specifics of interaction between rotavirus particles and host cells enabling invasion and infection have remained elusive. Host cell oligosaccharides are critical components, and their involvement aids the virus in cell-recognition and attachment, as well as dictation of the remarkable host-specificity that rotaviruses demonstrate. Interaction between the rotavirus spike-protein carbohydrate-binding domain (VP8*) and cell surface oligosaccharides facilitate virus recognition of host cells and attachment. Rotaviruses are considered, controversially, to recognise vastly different carbohydrate structures and either with incorporation of terminal sialic acid or without, as assessed by their ability to infect cells that have been pre-treated with sialidases. Herein, the X-ray crystallographic structures of VP8* from the sialidase insensitive Wa and the sialidase sensitive CRW-8 rotavirus strains that cause debilitating gastroenteritis in human and pig are reported. Striking differences are apparent regarding recognition of the sialic acid derivative methyl alpha-D-N-acetylneuraminide, presenting the first experimental evidence of the inability of the human rotavirus strain to bind this monosaccharide, that correlates with Wa and CRW-8 recognising sialidase-resistant and sialidase-sensitive receptors, respectively. Identified are structural features that provide insight in attainment of substrate specificity exhibited by porcine strains as compared to rhesus rotavirus. Revealed in the CRW-8 VP8* structure is an additional bound ligand that intriguingly, is within a cleft located equivalent to the carbohydrate-binding region of galectins, and is suggestive of a new region for interaction with cell-surface carbohydrates. This novel result and detailed comparison of our representative sialidase-sensitive CRW-8 and insensitive Wa VP8* structures with those reported leads to our hypothesis that this groove is used for binding carbohydrates, and that for the human strains, as for other sialidase-insensitive strains could represent a major oligosaccharide-binding region.