Background
Human rotaviruses (RVs) are the major etiological agent of acute gastroenteritis in infants and young children worldwide. Rotavirus can cause severe gastroenteritis, and rotavirus-related diarrhea leads to about 450,000 deaths globally each year [
1,
2]. Rotavirus, belonging to the
Reoviridae family, possesses 11 segments of double-stranded RNA encoding 12 proteins, including six structural proteins (VP1, VP2, VP3, VP4, VP6, and VP7) and six nonstructural proteins (NSP1 to NSP6). Based on the sequence variability of the outer capsid glycoprotein VP7 and protease-sensitive spike protein VP4, group A rotavirus, the most common species, is classified into various G and P types respectively. The current evidence indicates that there exists at least 27 G and 37 P genotypes [
3,
4]. G1-G4, G9, G12, P [4], P [6], and P [8] are considered as the common human rotavirus genotypes [
5].
The rotavirus P [10] is an unusual genotype, which was first identified in a human G8 RVA strain [
6,
7]. Since the first report in 1984, rotavirus P [10] strains have been detected occasionally with different G genotypes from different countries. The human P [10] rotavirus prototype strain 69 M as well as B37 were G8P [10]. There were G9P [10] strains found in Ghana [
8]. P [10] was also found in combination with G3 human genotype with severe infantile diarrhea [
9,
10]. Group A rotaviruses can infect both humans and animals. The P [10] rotavirus is predominantly found in humans. In animals, P [10] strain was identified from swine in Denmark with unknown VP7 genotype, and a strain of G3P [10] was identified from a bat in China [
11,
12].
The first step of rotavirus infection involves the recognition of specific cell surface glycans in the initial cell attachment step. Recent studies indicate that RVs recognize histo-blood group antigens (HBGAs) as potential receptors [
13‐
15]. The attachment of RV to cell surface carbohydrates is mediated by the VP8* domain of the spike protein VP4. RV with different genotypes recognizes various carbohydrate ligands. Significant advances in understanding ligand-associated RVs have been made [
16‐
19]. P [10] was implied to possess the similar glycan binding specificity to P [19] VP8*. However, the specific glycan binding pattern and the interaction mechanisms of human rotavirus P [10] with the glycans remains limited. In this study, we explored the characterization of glycan binding specificity of human rotavirus P [10] by various assays.
Discussion
Group A rotaviruses are a major cause of acute childhood diarrhea. The human P [10] rotavirus strains were in association with strains of various genotypes. So far, few isolates of rotavirus P [10] have been reported in the literature. The molecular evolution of rotavirus P [10] remains unclear. The characterization of recognition patterns of P [10] with cellular glycans is required to elucidate the origin of RV P [10] and understanding on the epidemiology of the virus. In this study, We performed different assays to explore the receptor binding specificity of P [10] RV VP8*, including the oligosaccharide binding assay, saliva-based binding assay, and structural modeling.
Significant advancements have been made in elucidating RV and host interactions. Recent reports discovered that RVs recognize HBGAs as attachment factors or receptors. HBGAs are carbohydrates that distribute abundantly on mucosal epithelia of the body, and as soluble oligosaccharides in most body fluids except cerebrospinal fluid. HBGAs are polymorphic with different ABO, Lewis and secretor versus non-secretor types. RV-HBGA interactions correlate with the host susceptibility of RV infection and illness. RVs P [8] and P [4] preferably infect individuals who were secretors/partial secretors [
15]. Distinct genotypes of RVs recognize different HBGAs [
25‐
27]. In this study, P [10] RV VP8* bound to A-, B-, AB-type, secretor or non-secretor saliva samples, implying that P [10] RVs may have a broad binding range which was similar to the previous report [
23]. In the study by Liu et al., P [10] VP8* bound a low proportion of samples with no correlation to the ABH or Lewis types of the saliva donors. In our study the proportion of samples that bound with P [10] VP8* protein was high compared with previous study. We used the full sequence of P [10] VP8* for expression of VP8* protein, which was different with previous report. In addition, the VP8* sequences may be derived from different human RV P [10] strains and there maybe exist the potential difference. Otherwise, there exists other unknown attachment factors that still need to be explored to fully characterize the receptor binding specificity of P [10] RV.
Mucins are the main structural components of mucus. Mucin core 2 and mucin core 4 are commonly found in intestinal mucins. In humans, gastric and duodenal mucins generally contain the core 1 (Galβ1–3GalNAcα1-Ser/Thr) and the core 2 (Galβ1,3 (GlcNAcβ1,6) GalNAcα1-Ser/Thr) structures, and the core 3 (GlcNAcβ1,3GalNAcαSer/Thr) and core 4 (GlcNAcβ1,6 (GlcNAcβ1,3) GalNAcαSer/Thr) structures are predominant in the colon [
28]. Mucin glycans are reported to be important in the cell attachment of P[II] RVs [
19,
24]. Our result showed that P [10] VP8* protein recognized mucin core 2 and slightly mucin core 4 which was similar with that of P [19] VP8* protein. These data demonstrated that mucin glycans may be related with rotavirus P [10] infection.
The binding characterization of RV and cellular receptors plays a role in the cross-species transmission of RVs. The P [10] genotype belongs to the P[I] genogroup of group A rotaviruses. Most of RV genotypes in genogroup P[I] mainly infect animals, while the rotavirus P [10] strains were mainly identified from human infection [
6,
8‐
10,
29]. Previous studies have reported that human RV P [19] belonging to P[II] genogroup interacted with mucin core 2 [
19,
24]. P [10] RV VP8* binds to mucin core 2 using a potential glycan binding site that may be the same to P [19] VP8*. The homology modeling indicated that though two residues are different, all the residues displayed similar conformation and the four residues involved in hydrogen bonding interactions are the same, implying that P [10] VP8* may possess the same binding site and binds to mucin core 2 using similar mechanism. Sequence alignment showed that all P [10] strains had identical amino acid compositions on the deduced ligand binding site (data not shown). According to previous reports, alignment of the group A RV VP8* sequences showed that the amino acids of the mucin core 2 binding interface of the P [19] RVs are conserved among some other genotype RVs (P [4], P [6], P [8], P [10], and P [12]) [
24]. In the previous report by Liu et al., the identical glycan binding profiles was indicated for P [10] and P [19] RVs in the glycan array. Our study confirmed the suggestion by oligosaccharide binding assay and the homology modeling. Taken together, these data indicates that mucin core 2 may play an important role in the RV epidemiology and evolution.
Open AccessThis article is distributed under the terms of the Creative Commons Attribution 4.0 International License (
http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (
http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.