Mechanical unfolding of membrane proteins captured with single-molecule AFM techniques

Atomic force microscopy (AFM) is a powerful technique that enables to study biological macromolecules and dynamic biological processes at different scales. It is an excellent tool for imaging of biological objects under various conditions at a nanometer resolution. Force mode of AFM, so called single molecule force spectroscopy (SMFS), allows for investigation of the strength of molecular interactions of different origins established between and within biological molecules. In the present work, SMFS was used to detect and locate structurally and functionally important interactions of sodium/glycine betaine transporter BetP of Corynebacterium glutamicum, which serves as a model system for this class of proteins. Mechanical pulling of BetP molecules embedded into the lipid membranes resulted in a step-wise unfolding of the protein and revealed insights into its structural stability. Effect of the lipid environment, N- and C-terminal extensions on inramolecular interactions of BetP as well as protein activation and ligand binding were investigated in great detail. In another part of this work, I demonstrate an application of the AFM based technique that can record unfolding of a protein under force-clamp conditions. This method directly measures the kinetics of the protein unfolding, allowing for the use of simple methods to analyze the data. For the first time the force-clamp technique was used to describe in detail unfolding kinetics of the membrane protein, i. e. Na+/H+-antiporter NhaA from Escherichia coli. Performed here experiments on NhaA in its functionally active and inactive states demonstrated the advantages of examining unfolding kinetics at the single-molecule level. It was possible to observe unfolding events for pH-activated conformation of NhaA that due to the low frequency of occurrence were not represented in the ensemble average of the single-molecule measurements. As mechanical unfolding, similarly to bond rupture, is a force-dependent process, force-clamp technique can allow for a more direct way of probing protein unfolding and is anticipated to be also useful to examine the folding/unfolding kinetics of other membrane proteins.

Level thesis:degree_level

thesis.doctoral

Grantor dc:publisher

Technische Universität Dresden

Year

2008

Author dc:creator

• Baltrukovich, Natalya

Contributors dc:contributor

• Müller, Daniel J.
• Schwille, Petra
• Ziegler, Christine

• membrane proteins
• betp
• nhaa
• atomic force microscopy
• unfolding
• Rasterkraftmikriskopie
• Proteinfaltung