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Conformational Change of Bacteriorhodopsin Quantitatively Monitored by Microcantilever Sensors

Thomas Braun ^* , Natalija Backmann ^*, Manuel Vögtli ^*, Alexander Bietsch ^* , Andreas Engel , Hans-Peter Lang ^*, Christoph Gerber ^* and Martin Hegner ^*

^* National Center of Competence for Research in Nanoscale Science, Institute of Physics, and Maurice E. Müller Institute, Biozentrum, University of Basel, 4056 Basel, Switzerland; and IBM Zurich Research GmbH, 8803 Rüschlikon, Switzerland

Correspondence: Address reprint requests to Martin Hegner, Institute of Physics, NCCR "Nanoscale Science", Klingelbergstrasse 82, CH–4056 Basel, Switzerland. Tel.: 41-61-267-37-61; Fax: 41-61-267-37-84; E-mail: martin.hegner{at}unibas.ch.

Bacteriorhodopsin proteoliposomes were used as a model system to explore the applicability of micromechanical cantilever arrays to detect conformational changes in membrane protein patches. The three main results of our study concern: 1), reliable functionalization of micromechanical cantilever arrays with proteoliposomes using ink jet spotting; 2), successful detection of the prosthetic retinal removal (bleaching) from the bacteriorhodopsin protein by measuring the induced nanomechanical surface stress change; and 3), the quantitative response thereof, which depends linearly on the amount of removed retinal. Our results show this technique to be a potential tool to measure membrane protein-based receptor-ligand interactions and conformational changes.