On the computer screen, the model can be seen beginning to fold, then disappearing, and reappearing in succession, before the native state finally asserts itself. Pande and colleagues are trying to understand folding in terms of the chemical kinetics of the transition between these folded and unfolded states. Delineation of the transitional state could provide a breakdown into a series of phases in the folding event that could reveal general dynamic properties, he says. His team currently is employing electrophoresis, fluorescent energy transfer, and confocal microscopy to examine the folding and attachment during ribosomal self-assembly of an essential subunit called S15. They also are using optical tweezers to stretch molecules of titin, a protein involved in protecting muscles from overstretching, in an attempt to witness the formation of its subunits.
Protein is placed in a mixing device with a buffer that compresses it.
The protein folds as it flows out of the mixer. With this method, the researchers can monitor folding stages that occur in time intervals of less than 500 microseconds. One instrument now being used to study biomolecules manages to provide both the quantitative information prized by physicists and some of the intuitive information familiar to molecular biologists. And as the maths and physics take over, it becomes somewhat less intuitive. Relatively little is known for certain about the phases of protein folding.