title: Resolving structure and mechanical properties at the nanoscale of viruses with frequency modulation atomic force microscopy.
abstract: Structural Biology (SB) techniques are particularly successful in solving virus structures. Taking advantage of the symmetries, a heavy averaging on the data of a large number of specimens, results in an accurate determination of the structure of the sample. However, these techniques do not provide true single molecule information of viruses in physiological conditions. To answer many fundamental questions about the quickly expanding physical virology it is important to develop techniques with the capability to reach nanometer scale resolution on both structure and physical properties of individual molecules in physiological conditions. Atomic force microscopy (AFM) fulfills these requirements providing images of individual virus particles under physiological conditions, along with the characterization of a variety of properties including local adhesion and elasticity. Using conventional AFM modes is easy to obtain molecular resolved images on flat samples, such as the purple membrane, or large viruses as the Giant Mimivirus. On the contrary, small virus particles (25-50 nm) cannot be easily imaged. In this work we present Frequency Modulation atomic force microscopy (FM-AFM) working in physiological conditions as an accurate and powerful technique to study virus particles. Our interpretation of the so called "dissipation channel" in terms of mechanical properties allows us to provide maps where the local stiffness of the virus particles are resolved with nanometer resolution. FM-AFM can be considered as a non invasive technique since, as we demonstrate in our experiments, we are able to sense forces down to 20 pN. The methodology reported here is of general interest since it can be applied to a large number of biological samples. In particular, the importance of mechanical interactions is a hot topic in different aspects of biotechnology ranging from protein folding to stem cells differentiation where conventional AFM modes are already being used.
authors.affiliation: Departamento Física de la Materia Condensada, Universidad Autónoma de Madrid, Madrid, Spain.
authors.forename: David
authors.initials: D
authors.lastname: Martinez-Martin
authors.forename: Carolina
authors.initials: C
authors.lastname: Carrasco
authors.forename: Mercedes
authors.initials: M
authors.lastname: Hernando-Perez
authors.forename: Pedro J
authors.initials: PJ
authors.lastname: de Pablo
authors.forename: Julio
authors.initials: J
authors.lastname: Gomez-Herrero
authors.forename: Rebeca
authors.initials: R
authors.lastname: Perez
authors.forename: Mauricio G
authors.initials: MG
authors.lastname: Mateu
authors.forename: Jose L
authors.initials: JL
authors.lastname: Carrascosa
authors.forename: Daniel
authors.initials: D
authors.lastname: Kiracofe
authors.forename: John
authors.initials: J
authors.lastname: Melcher
authors.forename: Arvind
authors.initials: A
authors.lastname: Raman
mesh_terms: D000538:Aluminum Silicates / Q000737:chemistry; D000818:Animals; D001696:Biomechanical Phenomena; D055595:Mechanical Phenomena; D051379:Mice; D018625:Microscopy, Atomic Force / Q000379:methods*; D049329:Nanostructures; D017992:Parvovirus; D013499:Surface Properties; D014771:Virion
chemical_list: D000538:Aluminum Silicates; C011934:mica