Abstract
In situ atomic force microscopy (AFM) was used to investigate surface evolution during the growth of single crystals of turnip yellow mosaic virus (TYMV), cucumber mosaic virus (CMV) and glucose isomerase. Growth of these crystals proceeded by two-dimensional (2D) nucleation. For glucose isomerase, from supersaturation dependencies of tangential step rates and critical step length, the kinetic coefficients of the steps and the surface free energy of the step edge were calculated for different crystallographic directions. The molecular structure of the step edges, the adsorption of individual virus particles and their aggregates, and the initial stages of formation of 2D nuclei on the surfaces of TYMV and CMV crystals were recorded. The surfaces of individual TYMV virions within crystals were visualized, and hexameric and pentameric capsomers of the T=3 capsids were clearly resolved. This, so far as we are aware, is the first direct visualization of the capsomere structure of a virus by AFM. In the course of recording the in situ development of the TYMV crystals, 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.
Highlights
Recent years have seen the convergence of a variety of technologies for the determination of the structural and even dynamic properties of supramolecular assemblies [1,2]
Electron microscopy is used as a means of obtaining low-resolution phase information for complex assemblies such as large viruses [3], which is extended to high resolution by X-ray diffraction
Using in situ atomic force microscopy (AFM) we demonstrated that the growth of the (1 0 1) face of turnip yellow mosaic virus (TYMV) and the (1 1 0) face of cucumber mosaic virus (CMV) crystals proceeds strictly by two-dimensional nucleation
Summary
Recent years have seen the convergence of a variety of technologies for the determination of the structural and even dynamic properties of supramolecular assemblies [1,2]. Many viruses cannot be crystallized at all, or have unit cells beyond the range of X-ray crystallography In those cases, as suggested here, AFM may provide an insightful approach to study, large virus structure, and dynamic processes such as assembly and decapsidation [4,5]. In the past several years scanning tunneling microscopy (STM) has been successfully applied to studies of atomic mobility and surface evolution of crystalline materials grown in ultra high vacuum [6,7] These results have been used in a number of practical applications, including development of electronic, optoelectronic and superconducting devices. Sixtyfold symmetry provided by multiple identical protein subunits results in identical countenance from every direction These properties along with large size of virions make icosahedral viruses virtually a perfect system to study surface phenomena and growth mechanisms at molecular resolution, where even events involving an individual virus particle can be recorded. We describe here the results of studies of the surface morphology and kinetics of growth for glucose isomerase crystals
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