Sequence variation of koala retrovirus transmembrane protein p15E among koalas from different geographic regions
Yasuko Ishida^a,*,1, Chelsea McCallister^b,1, Nikolas Nikolaidis^b,1, Kyriakos Tsangaras^c, Kristofer M. Helgen^d, Alex D. Greenwood^c, Alfred L. Roca^a,e,**
a) Department of Animal Sciences, University of Illinois at Urbana-Champaign, 1207 W. Gregory Drive, Urbana, IL 61801, USA
b) Department of Biological Science and Center for Applied Biotechnology Studies, California State University, Fullerton, 800 North State College Blvd, Fullerton, CA 92834, USA
c) Leibniz Institute for Zoo and Wildlife Research, Alfred-Kowalke-Str. 17, 10315, Berlin, Germany
d) National Museum of Natural History, Smithsonian Institution, PO Box 37012, MRC 108, Washington, DC 20013, USA
e) The Institute for Genomic Biology, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA
The koala retrovirus (KoRV), which is transitioning from an exogenous to an endogenous form, has been associated with high mortality in koalas. For other retroviruses, the envelope protein p15E has been considered a candidate for vaccine development. We, therefore, examined proviral sequence variation of KoRV p15E in a captive Queensland and three wild southern Australian koalas. We generated 163 sequences with intact open reading frames, which grouped into 39 distinct haplotypes. Sixteen distinct haplotypes comprising 139 of the sequences (85%) coded for the same polypeptide. Among the remaining 23 haplotypes, 22 were detected only once among the sequences, and each had 1 or 2 non-synonymous differences from the majority sequence. Several analyses suggested that p15E was under purifying selection. Important epitopes and domains were highly conserved across the p15E sequences and in previously reported exogenous KoRVs. Overall, these results support the potential use of p15E for KoRV vaccine development.