Photoactive Yellow Protein: Converting Light into a Metastable Structural Change

Two questions at the forefront of biophysical sciences are biological sensing and energy conversion. Photoactive yellow protein is at the crossing point of these two topics as it converts light energy into a structural change in the process of biological light sensing. This bacterial photosensor is an excellent model system to study how a protein achieves such a function as it is relatively small and very stable. Over the years crystallography, spectroscopy, and multiscale modeling techniques have been applied to study the first step in the signal transduction process that it catalyzes- the ultrafast isomerization of the p-coumaric acid chromophore intrinsic to PYP. This has culminated in an ever-better understanding of the mechanism of its isomerization and the role of the protein in this process. Here we provide a review of the current state of knowledge on this issue.