Conformational Stability at Low Temperatures Using Single Protein Nanoaperture Optical Tweezers

Nanoaperture optical tweezers allow for trapping single proteins and detecting their conformational changes without modifying the protein, i.e., being free from labels or tethers. While past works have used laser heating as a way to vary the local temperature, this does not allow for probing of lower temperature values. Here we investigate the lower temperature dynamics of individual Bovine Serum Albumin (BSA) proteins with the help of a custom Peltier cooling stage. The BSA transitions between the normal (N) and fast (F) states. The normal form of BSA has a maximum occupancy at 21 +/- 1 degrees C, which is interpreted as its maximum stability point for the compact N form with respect to the F form. In this way, it is possible to find the relative thermodynamic parameters of single proteins without requiring any modifications to the intrinsic structure.