Vascular endothelial growth factors encoded by Orf virus show surprising sequence variation but have a conserved, functionally relevant structure

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 41n1 % 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 30n8 % with an average amino acid identity between pairs of NZ2-like sequences of 86n1 %. 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.

The genome of pseudocowpoxvirus: comparison of a reindeer isolate and a reference strain

“…It was demonstrated that all VEGFs of established PPV species (including PCPV VR634; Ueda et al, 2003) also possess the ability to induce endothelial proliferation and angiogenesis and are likely to be responsible for the highly vascularized and proliferative nature of PPV lesions (Savory et al, 2000;Wise et al, 2003;Inder et al, 2007;Ueda et al, 2003Ueda et al, , 2007. This is in spite of the fact that sequence variation of vVEGF proteins is remarkably high, varying from 35 to 63 % aa identity between species, whilst isolates of the same species show as little as 38 % aa sequence identity (Lyttle et al, 1994;Mercer et al, 2002Mercer et al, , 2006Wise et al, 2003Delhon Fig. 4.…”

Structural determinants of growth factor binding and specificity by VEGF receptor 2

“…All VEGF-A isoforms bind to VEGFR-1 and VEGFR-2, whereas PlGF and VEGF-B are specific for VEGFR-1. Furthermore, pox viruses encode VEGF variants collectively called VEGF-E that specifically bind to VEGFR-2 (23)(24)(25).…”

Crystal Structure of the Orf Virus NZ2 Variant of Vascular Endothelial Growth Factor-E

“…4, A and B, shows the critical residues determining receptor binding of VEGF-A, PlGF, and VEGF-E NZ7. These residues presumably also regulate receptor interaction of VEGF-E NZ2, Vammin, and VR-1 (29,32,48). The three loop regions, L1 (magenta), L2 (slate), and L3 (orange), that determine the interaction with VEGFR-1 and -2 (48) are marked.…”

“…In addition, we made the mutant VE R46I by exchanging Arg 46 with the corresponding amino acid in VEGF-A, Ile. This mutant was constructed to assess the importance of the previously postulated salt bridge between Arg 46 and Glu 64 that was suggested to block binding of VEGF-E to VEGFR-1 (29). Dimer formation of VEGF-E NZ2 mutants was determined by SDS-PAGE under reducing and nonreducing conditions after the proteins were deglycosylated with endoglycosidase F (supplemental Fig.…”

“…3 Supported by Grant 3100AO-100204 from the Swiss National Science Foundation. 4 To whom correspondence should be addressed: Paul Scherrer Institut, Labora sequence variation (29,30) yet show only 25-35% amino acid identity with VEGF-A. They lack a heparin binding domain, but some variants retain binding to neuropilin-1 (8,9).…”