Measurement of Protein Conformational Fluctuation in Ice by Passive Millimeter-Wave Microscopy

Thermal radiation emitted from an aqueous solution of bovine serum albumin (BSA) was measured and analyzed by passive millimeter-wave microscopy at a temperature range low enough to freeze water and to trap conformational intermediates in BSA. Experiments were performed at a millimeter-wave frequency of 50 GHz in a temperature range from 130 K to 270 K for a 20 % BSA aqueous solution, showing a displacement between two conformational states of BSA at a boundary temperature of approximately 190 K. Our microscope system using this freeze-trapping method is expected to provide noninvasive thermal images to enable novel high-throughput calorimetry useful for the analysis of protein functions.