The Effect of Proteolytic Cleavage of La Crosse Virus G1 Glycoprotein on Antibody Neutralization

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Abstract
Summary The envelope of the bunyavirus La Crosse contains two glycoproteins, G1 (120000 mol. wt.) and G2 (38000 mol. wt.). When incubated with trypsin or plasmin, the G1 glycoprotein of virus grown in cell culture was cleaved, leaving two different sized polypeptides in the envelope (67000 and 95000 mol. wt.). Chymotrypsin cleaved G1 leaving polypeptides of 70000 and 100000 mol. wt. G2, however, was not altered by these enzymes. When used in antibody neutralization studies, these proteolytically modified viruses were neutralized approximately 1 to 2 log10 units in 60 min while control virus was neutralized by over 4 log10 units in 20 min. Because antibody to G1, but not G2, was involved in La Crosse virus neutralization, cleavage of G1 appeared to be directly responsible for these altered kinetics of neutralization. Antibody did bind to the polypeptides remaining associated with the envelope resulting in infectious virus-antibody complexes. This indicated that a critical site in terms of antibody neutralization was removed from G1 by proteolytic enzymes.