On several previous occasions on this blog I've discussed proteins that undergo significant changes in structure without drastic changes in their primary sequence or solution conditions. In some cases, a few mutations can take a protein to a novel fold, as with Philip Bryan's protein G work. In others, closely related sequences within a whole family populate different kinds of folds, as Matt Cordes illustrated for the case of Cro proteins. In addition, there are some cases such as lymphotactin, where interconversion between two very different structures takes place at equilibrium, as illustrated by Brian Volkman's research. Each time stories like this come up I have mentioned that this kind of behavior (termed "metamorphism" in a 2008 commentary by Alexey Murzin) suggests a means by which proteins could evolve from one structure to another without losing foldedness or function. Recently, a group from the Weizmann Institute published results in PNAS that speak to this possibility.Although we are most familiar with the circadian rhythm from its effects on our physiological state, the roots of the phenomenon lie in the molecular biology of individual cells. The circadian rhythm is the result of a transcriptional control system that regulates the levels of many different proteins in the cell with the passing of time. Not all of the proteins subject to this control have yet been catalogued, and as a result some surprising effects are still being discovered. A recent article in Proceedings of the National Academy of Sciences from the Sancar lab at UNC suggests that circadian control of a DNA repair factor may be a way to enhance the effectiveness of a chemotherapeutic agent. The article is open access, so I encourage you to open it up and read along.
