Conformational changes preceding decapsidation of bromegrass mosaic virus under hydrostatic pressure: A small-angle neutron scattering study

The stability of bromegrass mosaic virus (BMV) and empty shells reassembled in vitro from purified BMV coat protein was investigated under hydrostatic pressure, using solution small-angle neutron scattering. This technique al lowed us to monitor directly the dissociation of the particles, and to dete ct conformational changes preceding dissociation. Significant dissociation rates were observed only if virions swelled upon increase of pressure, and pressure effects became irreversible at very high-pressure in such conditio ns. At pH 5.0, in buffers containing 0.5 M NaCl and 5 mM MgCl2, BMV remaine d compact (radius 12.9 nm), dissociation was limited to approximate to 10 % at 200 MPa, and pressure effects were totally reversible. At pH 5.9, BMV p articles were slightly swollen under normal pressure and swelling increased with pressure. The dissociation was reversible to 90% for pressures up to 160 MPa, where its rate-reached 28%, but became totally irreversible at 200 MPa. Pressure-induced swelling and dissociation increased further at pH 7. 3, but were essentially irreversible. The presence of (H2O)-H-2 in the buff er strongly stabilized BMV against pressure effects at pH 5.9, but not at p H 7.3. Furthermore, the reversible changes of the scattered intensity obser ved at pH 5.0 and 5.9 provide evidence that pressure could induce the relea se of coat protein subunits, or small aggregates of these subunits from the virions, and that the dissociated components reassociated again upon retur n to low pressure. Empty shells were stable at FH 5.0, at pressures up to 2 60 MPa. They became ill-shaped at high-pressure, however, and precipitated slowly after return to normal conditions, providing the first example of a pressure-induced conformational drift in an assembled system. (C) 2000 Acad emic Press.