Realtime Measurement of Mechanical Motion of Single Protein Molecules

Biomolecules, especially proteins, often consist of several rigid subunits and work like mechanical devices. Therefore their mechanical motion or the conformational dynamics are significantly investigated with a great deal of interests. However, it is a challenge to detect small mechanical motion, especially when its dimension is as small as several nanometers. Single molecule measurement technique making use of fluorescence resonance energy transfer (FRET) is one of effective solutions to observe molecular dynamics in very small dimensions like nanometers. We developed a single molecule measurement technique with improved time resolution. We employed the time stamp detection method to acquire the signals including rich information and the statistical data analysis to extract essential information from the signal. Using the new system, the conformational dynamics of cytochrome c (cyt c) protein molecules was investigated. The change of molecular structure is detected as that of the fluorescence intensity by way of FRET phenomenon. Some intermediate states were resolved and the time resolution in the order of millisecond was achieved.