Dynamic mechanism of the self-assembly process of tobacco mosaic virus protein studied by rapid temperature-jump small-angle X-ray scattering using synchrotron radiation

The self-assembly process of tobacco mosaic virus protein (TMVP) was observed by rapid temperature-jump time-resolved solution X-ray small-angle scattering using synchrotron radiation. The temperature-jump device used for the X-ray measurements is rapid enough to cope with even the fastest-assembling process of TMVP, and accumulates data of reasonable signal-to-noise ratios with a minimum total counting time of 7·5 seconds. The measurements suggested that the 20 S disk of TMVP polymerized to stacked disks (short rods). The time to complete stacking varied from approximately 25 seconds to approximately 1200 seconds, depending on the solution condition and magnitude of the temperature gap. Higher protein concentration, ionic strength and temperature favoured faster association. The results were analysed in terms of a set of kinetic equations that describe the two-stage aggregation of TMVP with an equilibrium constant K 1, and two rate constants k +2 and k −2 for association and dissociation of disks, respectively. The consistency of the analysis suggests that the TMVP assembly proceeds in two steps of: (1) the aggregation of A-proteins into double-layered disks; and (2) the stacking of double-layered disks. The kinetic analysis indicated that the stacking belongs to the lowest range of protein-protein interaction system.