title: Titin-Based Nanoparticle Tension Sensors Map High-Magnitude Integrin Forces within Focal Adhesions.
abstract: Mechanical forces transmitted through integrin transmembrane receptors play important roles in a variety of cellular processes ranging from cell development to tumorigenesis. Despite the importance of mechanics in integrin function, the magnitude of integrin forces within adhesions remains unclear. Literature suggests a range from 1 to 50 pN, but the upper limit of integrin forces remains unknown. Herein we challenge integrins with the most mechanically stable molecular tension probe, which is comprised of the immunoglobulin 27th (I27) domain of cardiac titin flanked with a fluorophore and gold nanoparticle. Cell experiments show that integrin forces unfold the I27 domain, suggesting that integrin forces exceed ∼30-40 pN. The addition of a disulfide bridge within I27 "clamps" the probe and resists mechanical unfolding. Importantly, incubation with a reducing agent initiates SH exchange, thus unclamping I27 at a rate that is dependent on the applied force. By recording the rate of S-S reduction in clamped I27, we infer that integrins apply 110 ± 9 pN within focal adhesions of rat embryonic fibroblasts. The rates of S-S exchange are heterogeneous and integrin subtype-dependent. Nanoparticle titin tension sensors along with kinetic analysis of unfolding demonstrate that a subset of integrins apply tension many fold greater than previously reported.
authors.affiliation: Department of Chemistry, Emory University , 1515 Dickey Drive, Atlanta, Georgia 30322, United States.
authors.forename: Kornelia
authors.initials: K
authors.lastname: Galior
authors.affiliation: Department of Chemistry, Emory University , 1515 Dickey Drive, Atlanta, Georgia 30322, United States.
authors.forename: Yang
authors.initials: Y
authors.lastname: Liu
authors.affiliation: Department of Chemistry, Emory University , 1515 Dickey Drive, Atlanta, Georgia 30322, United States.
authors.forename: Kevin
authors.initials: K
authors.lastname: Yehl
authors.affiliation: Department of Physics, Emory University , 400 Dowman Drive, Atlanta, Georgia 30322, United States.
authors.forename: Skanda
authors.initials: S
authors.lastname: Vivek
authors.affiliation: Department of Chemistry, Emory University , 1515 Dickey Drive, Atlanta, Georgia 30322, United States.
authors.forename: Khalid
authors.initials: K
authors.lastname: Salaita
mesh_terms: D000818:Animals; D002448:Cell Adhesion / Q000187:drug effects; D064211:Connectin / Q000737:chemistry*; D005347:Fibroblasts / Q000187:drug effects; D006046:Gold / Q000737:chemistry; D016023:Integrins / Q000737:chemistry*; D007700:Kinetics; D055595:Mechanical Phenomena; D053758:Nanoparticles / Q000008:administration & dosage / Q000737:chemistry*; D051381:Rats; D013314:Stress, Mechanical
chemical_list: D064211:Connectin; D016023:Integrins; D006046:Gold
keywords: Integrins; biophysics; focal adhesion; mechanotransduction