Force mode atomic force microscopy as a tool for protein folding studies

The advent of a new class of force microscopes designed specifically to "pull" biomolecules has allowed non-specialists to use force microscopy as a tool to study single-molecule protein unfolding. This powerful new technique has the potential to explore regions of the protein energy landscape that are not accessible in conventional bulk studies. It has the added advantage of allowing direct comparison with single-molecule simulation experiments. However, as with any new technique, there is currently no well described consensus for carrying out these experiments. Adoption of standard schemes of data selection and analysis will facilitate comparison of data from different laboratories and on different proteins. In this review, some guidelines and principles, which have been adopted by our laboratories, are suggested. The issues associated with collecting sufficient high quality data and the analysis of those data are discussed. In single-molecule studies, there is an added complication since an element of judgement has to be applied in selecting data to analyse; we propose criteria to make this process more objective.. The principal sources of error are identified and standardised methods of selecting and analysing the data are proposed. The errors associated with the kinetic parameters obtained from such experiments are evaluated. The information that can be obtained from dynamic force experiments is compared, both quantitatively and qualitatively to that derived from conventional protein folding studies. (C) 2002 Elsevier Science B.V. All rights reserved.