Inactivation of hantaviruses by N-ethylmaleimide preserves virion integrity

Thiol groups of cysteine residues are crucial for the infectivity of various enveloped viruses, but their role in the infectivity of viruses of the family Bunyaviridae has thus far not been studied. This report shows that thiol groups are essential to the infectivity of hantaviruses. Alkylation of the thiol functional groups using the membrane-permeable compound N-ethylmaleimide (NEM) and membrane-impermeable compound 5,5'-dithio-bis-(2-nitrobenzoic acid) (DTNB) showed NEM to be a highly effective inactivator of Puumala and Tula hantaviruses. The NEM-inactivated hantavirus maintained the buoyant density of the wild-type virus. Furthermore, the antigenicity of glycoproteins and the cell attachment capacity of virions were retained at NEM concentrations that totally abolished virus infectivity. These results signified preservation of virion integrity following inactivation with NEM, making chemically inactivated virions valuable research antigens. It was demonstrated with biotin-conjugated maleimide, a mechanistic analogue of NEM, that all the structural proteins of hantavirus were sensitive towards thiol alkylation. In contrast to hantaviruses, NEM did not abolish Uukuniemi phlebovirus infectivity to the same extent. This indicates differences in the use of free thiols in virus entry among members of the family Bunyaviridae.