Large-plaque mutants of sindbis virus show reduced binding to heparan sulfate, heightened viremia, and slower clearance from the circulation

Laboratory strains of Sindbis virus must bind to the negatively charged gly cosaminoglycan heparan sulfate in order to efficiently infect cultured cell s, During infection of mice, however, we have frequently observed the devel opment of large-plaque viral mutants with a reduced ability to bind to hepa ran sulfate. Sequencing of these mutants revealed changes of positively cha rged amino acids in putative heparin-binding domains of the E2 glycoprotein , Recombinant viruses were constructed with these changes as single amino a cid substitutions in a strain Tote 1101 background, All exhibited decreased binding to heparan sulfate and had larger plaques than Tote 1101. When inj ected subcutaneously into neonatal mice, large-plaque viruses produced high er-titer viremia and often caused higher mortality, Because circulating hep arin-binding proteins are known to be rapidly sequestered by tissue heparan sulfate, we measured the kinetics of viral clearance following intravenous injection. Much of the parental small-plaque Tote 1101 strain of Sindbis v irus was cleared from the circulation by the liver,within minutes, in contr ast to recombinant large-plaque viruses, which had longer circulating half- lives. These findings indicate that a decreased ability to bind to heparan sulfate allows more efficient viral production in vivo, which may in turn l ead to increased mortality. Because Sindbis virus is only one of a growing number of viruses from many families which have been shown to bind to hepar an sulfate, these results may be generally applicable to the pathogenesis o f such viruses.