Molecular characterization of morphologically typical human calicivirus Sapporo

Abstract

Human calicivirus Sapporo (SV) has typical calicivirus morphology and causes acute gastroenteritis in children. The nucleotide sequence of 3.2 kb of the 3' end of SV was determined from a cloned cDNA. The 3' end of the SV genome is predicted to encode the RNA-dependent RNA polymerase region, the capsid protein and two small open reading frames. The nonstructural and capsid protein coding sequences in the SV genome are fused in a single open reading frame. The organization of these proteins in the SV sequence is similar to that of rabbit hemorrhagic disease virus and the recently described Manchester virus, and distinct from the genome organization of the prototype human calicivirus, Norwalk virus, that lacks typical calicivirus morphology and has been described as a small round structured virus (SRSV). Sequence analysis of the predicted capsid region showed that the SV capsid is longer by approximately 30 amino acids than the capsid of any of the SRSVs, and multiple sequence alignments showed that these additional amino acids are located in the variable region of the capsid protein. Expression of the capsid protein of SV in insect cells resulted in the self-assembly of virus-like particles that have a morphology similar to that of the native virus. This result shows that calicivirus morphology is determined by the primary sequence of the capsid protein.

Genetic classification of "Sapporo-like viruses"

“…The genomic organisation of SLVs is distinct from that of NLVs [24,29]. NLVs possess three different open reading frames (ORFs), consisting of a 5 ORF encoding for the non-structural proteins, including the RNA polymerase, a second ORF encoding for the major capsid protein and a 3 ORF encoding for a basic minor structural protein [5,6,11].…”

“…NLVs possess three different open reading frames (ORFs), consisting of a 5 ORF encoding for the non-structural proteins, including the RNA polymerase, a second ORF encoding for the major capsid protein and a 3 ORF encoding for a basic minor structural protein [5,6,11]. In SLVs, the polyprotein gene is fused to and in frame with the capsid coding region [24,29]. In addition, in all published SLV strains except a human strain, London/92 and a porcine strain, PEC/Cowden [5,15,18,27,29,40], an additional ORF has been predicted in +1 frame, overlapping the N terminus of the capsid gene (capsid overlap).…”

“…In SLVs, the polyprotein gene is fused to and in frame with the capsid coding region [24,29]. In addition, in all published SLV strains except a human strain, London/92 and a porcine strain, PEC/Cowden [5,15,18,27,29,40], an additional ORF has been predicted in +1 frame, overlapping the N terminus of the capsid gene (capsid overlap). To date, the sequence of a ∼3-kb region extending from the RNA polymerase gene to the 3 poly(A) tail is available in GenBank for 9 NLV strains, of which 6 have had their entire genome sequenced: Norwalk/68 [17], Southampton/91 [22], Lordsdale/93 [9], Camberwell/94 [3,36], Chiba/87 (GenBank accession number No.…”

“…In addition, a porcine enteric calicivirus (PEC) has recently been shown to be related to the SLV genus and to belong to a fifth genetic cluster [15]. To date, human SLVs, within the family Caliciviridae, have often been considered to belong to a single genogroup, GIII, comparable with the two genogroups of NLVs, GI and GII [13,29,40,41]. However, Jiang et al have suggested the possible existence of two genogroups among human SLVs [18].…”

Development of an Enzyme Immunoassay for Detection of Sapovirus-Specific Antibodies and Its Application in a Study of Seroprevalence in Children

“…Baculovirus expression and VLP formation of SV capsid proteins have also been reported (10,12,19,30); however, the yield of SV VLPs obtained is typically low. Since there are very limited reports on the seroprevalence of SVs (26,28,29,36), in this article we describe the bacterial expression of SV capsid fusion proteins, the development of an EIA for measuring anti-SV antibodies, and its application in a study of SV seroprevalence in children.…”