Surface processes in the crystallization of turnip yellow mosaic virus visualized by atomic force microscopy

In situ atomic force microscopy (AFM) was used to investigate surface evolu tion during the growth of single crystals of turnip yellow mosaic virus (TY MV). Growth of the (101) face of TYMV crystals proceeded by two-dimensional nucleation, The molecular structure of the step edges and adsorption of in dividual virus particles and their aggregates on the crystalline surface we re recorded. The surfaces of individual virions within crystals were visual ized and seen to be quite distinctive with the hexameric and pentameric cap somers of the T = 3 capsids being clearly resolved. This, so far as we are aware, is the first direct visualization of the capsomere structure of a vi rus by AFM. In the course of recording the in situ development of the cryst als, a profound restructuring of the surface arrangement was observed. This transformation was highly cooperative in nature, but the transitions were unambiguous and readily explicable in terms of an organized loss of classes of virus particles from specific lattice positions. In some cases areas of a single crystal surface were recorded in which mere captured successive p hases of the transition. We believe this provides the first visual record o f a cooperative restructuring of the surface of a supramolecular crystal. ( C) 1999 Academic Press.