Digital force-feedback for protein unfolding experiments using atomic force microscopy Journal Article


Author(s): Bippes, Christian A; Janovjak, Harald; Kedrov, Alexej; Mueller, Daniel J
Article Title: Digital force-feedback for protein unfolding experiments using atomic force microscopy
Affiliation
Abstract: Since its invention in the 1990s single-molecule force spectroscopy has been increasingly applied to study protein (un-)folding, cell adhesion, and ligand–receptor interactions. In most force spectroscopy studies, the cantilever of an atomic force microscope (AFM) is separated from a surface at a constant velocity, thus applying an increasing force to folded bio-molecules or bio-molecular bonds. Recently, Fernandez and co-workers introduced the so-called force-clamp technique. Single proteins were subjected to a defined constant force allowing their life times and life time distributions to be directly measured. Up to now, the force-clamping was performed by analogue PID controllers, which require complex additional hardware and might make it difficult to combine the force-feedback with other modes such as constant velocity. These points may be limiting the applicability and versatility of this technique. Here we present a simple, fast, and all-digital (software-based) PID controller that yields response times of a few milliseconds in combination with a commercial AFM. We demonstrate the performance of our feedback loop by force-clamp unfolding of single Ig27 domains of titin and the membrane proteins bacteriorhodopsin (BR) and the sodium/proton antiporter NhaA.
Journal Title: Nanotechnology
Volume: 18
Issue 4
ISSN: 0957-4484
Publisher: IOP Publishing Ltd.  
Date Published: 2007-01-31
Start Page: 044022
DOI: 10.1088/0957-4484/18/4/044022
Open access: no