ABSTRACT
The first report of a vascular endothelial growth factor (VEGF)-like gene in Orf virus included the surprising observation that the genes from two isolates (NZ2 and NZ7) shared only 41.1% amino acid sequence identity. We have examined this sequence disparity by determining the VEGF gene sequence of 21 isolates of Orf virus derived from diverse sources. Most isolates carried NZ2-like VEGF genes but their predicted amino acid sequences varied by up to 30.8% with an average amino acid identity between pairs of NZ2-like sequences of 86.1%. This high rate of sequence variation is more similar to interspecies than intraspecies variability. In contrast, only three isolates carried an NZ7-like VEGF gene and these varied from the NZ7 sequence by no more than a single nucleotide. The VEGF family are ligands for a set of tyrosine kinase receptors. The viral VEGFs are unique among the family in that they recognize VEGF receptor 2 (VEGFR-2) but not VEGFR-1 or VEGFR-3. Comparisons of the viral VEGFs with other family members revealed some correlations between conserved residues and the ability to recognize specific VEGF receptors. Despite the sequence variations, structural predictions for the viral VEGFs were very similar to each other and to the structure determined by X-ray crystallography for human VEGF-A. Structural modelling also revealed that a groove seen in the VEGF-A homodimer and believed to play a role in its binding to VEGFR-1 is blocked in the viral VEGFs. This may contribute to the inability of the viral VEGFs to bind VEGFR-1.
Subject(s)
Conserved Sequence , Endothelial Growth Factors , Endothelial Growth Factors/genetics , Genetic Variation , Intercellular Signaling Peptides and Proteins , Lymphokines , Orf virus/genetics , Sheep Diseases/virology , Viral Proteins/genetics , Amino Acid Motifs , Amino Acid Sequence , Animals , Binding Sites , Cattle , Cell Line , Crystallography, X-Ray , Endothelial Growth Factors/chemistry , Endothelial Growth Factors/metabolism , Intercellular Signaling Peptides and Proteins/chemistry , Intercellular Signaling Peptides and Proteins/genetics , Intercellular Signaling Peptides and Proteins/metabolism , Lymphokines/chemistry , Lymphokines/genetics , Lymphokines/metabolism , Models, Molecular , Molecular Sequence Data , Protein Structure, Tertiary , Sequence Homology, Amino Acid , Sheep , Vascular Endothelial Growth Factor A , Vascular Endothelial Growth Factor Receptor-1 , Vascular Endothelial Growth Factor Receptor-2 , Vascular Endothelial Growth Factor Receptor-3 , Vascular Endothelial Growth Factors , Viral Proteins/chemistry , Viral Proteins/metabolismABSTRACT
Orf virus is a large DNA virus and is the type species of the Parapoxvirus genus of the family Poxviridae. Orf virus infects the epithelium of sheep and goats and is transmissible to humans. Recently we discovered a gene in orf virus that encodes a polypeptide with remarkable homology to mammalian interleukin (IL-10) and viral encoded IL-10s of herpes viruses. The predicted polypeptide sequence shows high levels of amino acid identity to IL-10 of sheep (80%), cattle (75%), humans (67%) and mice (64%), as well as IL-10-like proteins of Epstein-Barr virus (63%) and equine herpes virus (67%). The C-terminal region, comprising two-thirds of the orf virus protein, is identical to ovine IL-10 which suggests that this gene has been captured from its host sheep during the evolution of orf virus. In contrast the N-terminal region shows little homology with cellular IL10s and in this respect resembles other viral IL-10s. IL-10 is a pleiotrophic cytokine that can exert either immunostimulatory or immunosuppressive effects on many cell types. IL-10 is a potent anti-inflammatory cytokine with inhibitory effects on non-specific immunity in particular macrophage function and Thl effector function. Our studies so far, indicate, that the functional activities of orf virus IL-10 are the same as ovine IL-10. Orf virus IL-10 stimulates mouse thymocyte proliferation and inhibits cytokine synthesis in lipopolysaccharide-activated ovine macrophages, peripheral blood monocytes and keratinocytes. Infection of sheep with an IL-10 deletion mutant of orf virus has shown that interferon-gamma levels are higher in tissue infected with the mutant virus than the parent virus. The functional activities of IL-10 and our data on orf virus IL-10 suggest a role in immune evasion.
Subject(s)
Interleukin-10/genetics , Orf virus/genetics , Amino Acid Sequence , Animals , Base Sequence , Ecthyma, Contagious/virology , Humans , Interleukin-10/chemistry , Interleukin-10/metabolism , Molecular Sequence Data , Orf virus/immunology , Sequence Homology, Nucleic AcidABSTRACT
A gene encoding a polypeptide with homology to interleukin-10 (IL-10) has been discovered in the genome of orf virus (OV) strain NZ2, a parapoxvirus that infects sheep, goats, and humans. The predicted polypeptide sequence shows high levels of amino acid identity to IL-10 of sheep (80%), cattle (75%), humans (67%), and mice (64%), as well as IL-10-like proteins of Epstein-Barr virus (63%) and equine herpesvirus (67%). The C-terminal region, comprising two-thirds of the OV protein, is identical to ovine IL-10, which suggests that this gene has been captured from its host sheep during the evolution of OV. The IL-10-like gene is transcribed early. Conditioned medium from COS cells transfected with a eukaryotic expression vector containing the OV IL-10-like gene showed the same biological activity as ovine IL-10 in a murine thymocyte proliferation assay. OV IL-10 is likely to be important in immune evasion by OV, since IL-10 is a multifunctional cytokine that has inhibitory effects on nonspecific immunity and Th1 effector function.
