Transition paths of protein-folding probed with optical tweezers

Proteins are essential for life. To be able to perform their tasks, proteins need to fold into their functional form. From a physicist's perspective, nature solves this 'folding problem' by providing a multidimensional energy landscape which efficiently guides a loose peptide towards a distinct 3D structure which is solely predefined by its unique amino acid sequence. A powerful method to directly study the folding mechanics of proteins is single-molecule force spectroscopy, which is used in this thesis. With a variety of sophisticated analysis tools it is possible to derive transition state positions and barrier heights up to entire one-dimensional projections of the folding energy landscapes of proteins from single-molecule trajectories. Recent technological advances to improve temporal and spatial resolution have opened doors towards directly accessing protein folding transition paths. The establishment of appropriate transition path analysis techniques and their correct interpretation is one of the main objectives of this work. Here, three key questions are being addressed: 1. What does energy landscape roughness mean? 2. How and what can we learn from studying transition paths? 3. Are natural and artificial proteins mechanically different? In addition to its new findings, this work provides a valuable compact overview of state-of-the-art analysis methods for single-molecule force spectroscopy data. Therefore, care has been taken to provide enough details and information to enable the reader to reproduce all crucial lines of thought.