[Modification of tobacco mosaic virus envelope protein using trinitrobenzenesulfonic acid]

The process of modification of tobacco mosaic virus (TMV) coat protein with a lysine-specific reagent trinitrobenzenesulfonic acid (TNBS) was studied. TMV coat protein molecule is known to contain just two Lys residues (K53 and K68) localized in the same region of TMV coat protein subunit tertiary structure at a distance of about 70Ao from the virion axis. TNBS was used to modify the coat protein of wild type (U1) TMV and that of a coat protein ts-mutant ts21-66, bearing two amino-acid substitutions (I21 T and D66 G), both localized in the 70Ao region. In the mutant coat protein, TNBS modification rate for one of the two Lys residues was found to increase drastically (7 to 8 times) between 30 and 32o at pH 8.0. In U1 coat protein a similar increase was observed for one of Lys residues at 36o and pH 8.6. The results may indicate that the 70Ao region represents the labile section of TMV coat protein molecule, and gradual destruction of this site results first in loss of protein capacity to form well arranged two-cylindrical aggregates and then (after slight heating) in loss of capacity to form ordered helical aggregates.