title: Frequency modulation atomic force microscopy reveals individual intermediates associated with each unfolded I27 titin domain.
abstract: In this study, we apply a dynamic atomic force microscopy (AFM) technique, frequency modulation (FM) detection, to the mechanical unfolding of single titin I27 domains and make comparisons with measurements made using the AFM contact or static mode method. Static mode measurements revealed the well-known force transition occurring at 100-120 pN in the first unfolding peak, which was less clear, or more often absent, in the subsequent unfolding peaks. In contrast, some FM-AFM curves clearly resolved a force transition associated with each of the unfolding peaks irrespective of the number of observed unfolded domains. As expected for FM-AFM, the frequency shift response of the main unfolding peaks and their intermediates could only be detected when the oscillation amplitudes used were smaller than the interaction lengths being measured. It was also shown that the forces measured for the dynamical interaction of the FM-AFM technique were significantly lower than those measured using the static mode. This study highlights the potential for using dynamic AFM for investigating biological interactions, including protein unfolding and the detection of novel unfolding intermediates.
authors.affiliation: Centre for Research on Adaptive Nanodevices and Nanostructures (CRANN), University of Dublin, Trinity College, Dublin 2, Ireland. michael.higgins@tcd.ie
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Higgins
authors.forename: John E
authors.initials: JE
authors.lastname: Sader
authors.forename: Suzanne P
authors.initials: SP
authors.lastname: Jarvis
mesh_terms: D000538:Aluminum Silicates; D001703:Biophysics / Q000379:methods*; D002138:Calibration; D064211:Connectin; D008280:Magnetics; D018625:Microscopy, Atomic Force / Q000379:methods*; D015233:Models, Statistical; D009124:Muscle Proteins / Q000737:chemistry; D009991:Oscillometry; D010455:Peptides / Q000737:chemistry; D011138:Polytetrafluoroethylene; D011489:Protein Denaturation; D017510:Protein Folding; D011494:Protein Kinases / Q000737:chemistry; D017434:Protein Structure, Tertiary; D011994:Recombinant Proteins / Q000737:chemistry; D012984:Software
chemical_list: D000538:Aluminum Silicates; D064211:Connectin; D009124:Muscle Proteins; D010455:Peptides; D011994:Recombinant Proteins; D011138:Polytetrafluoroethylene; D011494:Protein Kinases; C011934:mica