Optical Tweezers to Study Viruses
A virus is a complex molecular machine that propagates by channeling its genetic information from cell to cell. Unlike macroscopic engines, it operates in a nanoscopic world under continuous thermal agitation. Viruses have developed efficient passive and active strategies to pack and release nucleic acids. Some aspects of the dynamic behavior of viruses and their substrates can be studied using structural and biochemical techniques. Recently, physical techniques have been applied to dynamic studies of viruses in which their intrinsic mechanical activity can be measured directly. Optical tweezers are a technology that can be used to measure the force, torque and strain produced by molecular motors, as a function of time and at the single-molecule level. Thanks to this technique, some bacteriophages are now known to be powerful nanomachines; they exert force in the piconewton range and their motors work in a highly coordinated fashion for packaging the viral nucleic acid genome. Nucleic acids, whose elasticity and condensation behavior are inherently coupled to the viral packaging mechanisms, are also amenable to examination with optical tweezers. In this chapter, we provide a comprehensive analysis of this laser-based tool, its combination with imaging methods and its application to the study of viruses and viral molecules.
KeywordsBiophysics Virus Bacteriophage Capsid DNA RNA Molecular motor Machine Single-molecule Mechanochemistry Optics Optical tweezers Magnetic tweezers Dynamics Manipulation Force Pressure Elasticity Condensation DNA packaging
Atomic force microscopy
It is a pleasure to acknowledge J.R. Moffitt and J.L. Carrascosa for technical insights into different aspects of the chapter, R. Bocanegra, L. Quintana for careful reading of the manuscript, C. Mark and S. Hormeño for editorial and illustration assistance, respectively, and M. de la Guía for graphic design of Fig. 9.8. This work was funded by the Spanish Ministry of Science and Innovation under the “Ramon y Cajal” program (Grant No. RYC-2007-01765).
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