Vaccinia virus has a wide host range and infects mammalian cells of many different species. This suggests that the
cell surface receptors for vaccinia virus are ubiquitously expressed and highly conserved. Alternatively, different receptors are used for vaccinia virus
infection of different cell types. Here we report that vaccinia virus binds to
heparan sulfate, a
glycosaminoglycan (GAG) side chain of cell surface
proteoglycans, during
virus infection. Soluble
heparin specifically inhibits vaccinia virus binding to cells, whereas other GAGs such as condroitin
sulfate or dermantan
sulfate have no effect.
Heparin also blocks
infections by cowpox virus, rabbitpox virus, myxoma virus, and Shope fibroma virus, suggesting that cell surface
heparan sulfate could be a general mediator of the entry of poxviruses. The biochemical nature of the
heparin-blocking effect was investigated.
Heparin analogs that have acetyl groups instead of
sulfate groups also abolish the inhibitory effect, suggesting that the negative charges on GAGs are important for
virus infection. Furthermore, BSC40 cells treated with
sodium chlorate to produce undersulfated GAGs are more refractory to vaccinia virus
infection. Taken together, the data support the notion that cell surface
heparan sulfate is important for vaccinia virus
infection. Using
heparin-Sepharose beads, we showed that vaccinia virus virions bind to
heparin in vitro. In addition, we demonstrated that the recombinant A27L gene product binds to the
heparin beads in vitro. This
recombinant protein was further shown to bind to cells, and such interaction could be specifically inhibited by soluble
heparin. All the data together indicated that A27L
protein could be an attachment
protein that mediates vaccinia virus binding to cell surface
heparan sulfate during
viral infection.