Abstract
Photoactive yellow protein (PYP), a structural prototype of PAS domain proteins, is a photosensor protein of the purple photosynthetic bacteria. PYP has a trans-4-hydroxycinnamic acid chromophore binding to a cysteine residue via a thioester bond. PYP chromophore maximally absorbs a blue light at 446 nm. It is isomerized to cis form on photon absorption and PYP undergoes the photocycle in which several spectroscopically distinct intermediates are formed. During the photocycle, the global protein conformational change takes place and near-UV intermediate, a putative signaling state, is formed. Recent studies have suggested that the structural changes are propagated across the central -sheet through the weak interactions such as CH/π and CH/O interactions as well as conventional hydrogen bonds. The similarities in photoreaction mechanisms between PYP and LOV domain proteins will be discussed.
