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Single M13 bacteriophage tethering and stretching (Cover Article)


Khalil A.S. , Ferrer J.M. , Brau R.R. , Kottmann S.T. , Noren C.J. , Lang M.J. , Belcher A.M. . PNAS. 2007 ; 104(12). 4892-4897


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The ability to present biomolecules on the highly organized struc- ture of M13 filamentous bacteriophage is a unique advantage. Where previously this viral template was shown to direct the orientation and nucleation of nanocrystals and materials, here we apply it in the context of single-molecule (SM) biophysics. Genet- ically engineered constructs were used to display different reactive species at each of the filament ends and along the major capsid, and the resulting hetero-functional particles were shown to con- sistently tether microscopic beads in solution. With this system, we report the development of a SM assay based on M13 bacterio- phage. We also report the quantitative characterization of the biopolymer’s elasticity by using an optical trap with nanometer- scale position resolution. Expanding the fluctuating rod limit of the wormlike chain to incorporate enthalpic polymer stretching yielded a model capable of accurately capturing the full range of extensions. Fits of the force-extension measurements gave a mean persistence length of 1,265 nm, lending SM support for a shorter filamentous bacteriophage persistence length than previously thought. Furthermore, a predicted stretching modulus roughly two times that of dsDNA, coupled with the system’s linkage versatility and load-bearing capability, makes the M13 template an attractive candidate for use in tethered bead architectures.