Chikungunya virus (CHIKV) is a reemerging arbovirus responsible for outbreaks of infection throughout Asia and Africa, causing an acute illness characterized by fever, rash, and polyarthralgia. Although CHIKV infects a broad range of host cells, little is known about how CHIKV binds and gains access to the target cell interior. In this study, we tested whether glycosaminoglycan (GAG) binding is required for efficient CHIKV replication using CHIKV vaccine strain 181/25 and clinical isolate SL15649. Preincubation of strain 181/25, but not SL15649, with soluble GAGs resulted in dose-dependent inhibition of infection. While parental Chinese hamster ovary (CHO) cells are permissive for both strains, neither strain efficiently bound to or infected mutant CHO cells devoid of GAG expression. Although GAGs appear to be required for efficient binding of both strains, they exhibit differential requirements for GAGs, as SL15649 readily infected cells that express excess chondroitin sulfate but that are devoid of heparan sulfate, whereas 181/25 did not. We generated a panel of 181/25 and SL15649 variants containing reciprocal amino acid substitutions at positions 82 and 318 in the E2 glycoprotein. Reciprocal exchange at residue 82 resulted in a phenotype switch; Gly82 results in efficient infection of mutant CHO cells but a decrease in heparin binding, whereas Arg82 results in reduced infectivity of mutant cells and an increase in heparin binding. These results suggest that E2 residue 82 is a primary determinant of GAG utilization, which likely mediates attenuation of vaccine strain 181/25
