Atomic Force Microscopy Investigation of Viruses

Abstract

Atomic force microscopy (AFM) has proven to be a valuable approach to delineate the architectures and detailed structural features of a wide variety of viruses. These have ranged from small plant satellite viruses of only 17 nm to the giant mimivirus of 750 nm diameter, and they have included diverse morphologies such as those represented by HIV, icosahedral particles, vaccinia, and bacteriophages. Because it is a surface technique, it provides images and information that are distinct from those obtained by electron microscopy, and in some cases, at even higher resolution. By enzymatic and chemical dissection of virions, internal structures can be revealed, as well as DNA and RNA. The method is relatively rapid and can be carried out on both fixed and unfixed samples in either air or fluids, including culture media. It is nondestructive and even non-perturbing. It can be applied to individual isolated virus, as well as to infected cells. AFM is still in its early development and holds great promise for further investigation of biological systems at the nanometer scale.Key words: Imaging, Nanoscale, Structure, Infection, Nucleic acids, Icosahedra A direct imaging technology that promises to have a significant impact on structural biology, and which is, in most ways, complementary to X-ray diffraction and electron microscopy, the classical approaches, is atomic force microscopy (AFM) (1-3). An immediate advantage of AFM is that it is based on relatively simple physical principles, unlike X-ray crystallography, and the instruments are mechanically and electronically rather straightforward, unlike electron microscopy. Unlike both of the other technologies, AFM is fairly inexpensive to institute and apply, even to biological specimens. The acuity and investigative size range of the AFM have proven to be quite remarkable and it is now permitting researchers new access to virus structure and the effects of viruses on organisms. Indeed, it has allowed us to

Mechanical stiffening of human rhinovirus by cavity-filling antiviral drugs

“…For topographic and mechanical analyses by AFM of HRV14 virions in liquid we used purified virus suspensions that were diluted enough to obtain well-separated particles adsorbed onto a solid substrate. Based on previous experiences on imaging HRV 64 and other virus particles, 15,16,65 using AFM, various substrates (including glass, silanized glass and freshly cleaved mica) and buffer solutions (Tris buffer at neutral pH containing Ni 2+ ions 64 and phosphate-buffered saline, PBS) were tested. With any of those substrates and buffers, and using the cantilevers we had extensively used for AFM analysis of other viruses, 23 we encountered three difficulties for regular high-resolution imaging and mechanical analysis of HRV virions: i) non-specific force peaks appeared with some frequency due to adhesion between particle and cantilever tip; ii) some particles were disrupted during small-field scanning ( Fig.…”

Acanthamoeba polyphaga mimivirus and other giant viruses: an open field to outstanding discoveries

“…First of all, their enormous size of approximately 700 nm lets them be retained on 0,2 μm filters [5] (Figure 1-A to D). APMV particles do not have an outer envelope, but fibers of approximately 120 nm can be associated with the capsid [58,59] (Figure 1-A and B). These fibers, still under investigation, may be involved in viral adsorption to substrates.…”

Algal Viruses: The (Atomic) Shape of Things to Come

“…Although impressive, and a demonstration of the power in directly mapping a surface, this technique did not offer the advantages expected from AFM, namely viral investigation in, or at near physiological conditions due to limitations in viral preparation methods and knowledge at that time. The year of 2001 took the technology, in one aspect, closer to this goal, with the imaging of free virus directly adsorbed to mica substrate by AFM analysis in liquid [ 48 ]. Icosahedral viruses such as satellite tobacco mosaic virus, brome mosaic virus and cauliflower mosaic virus yielded capsomeric structure without the use of a crystalline lattice.…”