Photoactive yellow protein

[1] A recently (2016) developed chemogenetic system named FAST (Fluorescence-Activating and absorption Shifting Tag) was engineered from PYP to specifically and reversibly bind a series of hydroxybenzylidene rhodanine (HBR) derivatives for their fluorogenic properties.

These structural studies have provided insight into photosensitive proteins, e.g. the role of hydrogen bonding, molecular isomerization and photoactivity.

[8] Scientists were therefore amazed when the PYP Cys 69 was bound by a thiol ester linkage as the light sensitive prosthetic group p-coumaric acid.

[3] During the photoreactive mechanism:[3][8] These observed phenomena are due to the trans–cis isomerization of the vinyl trans double bond in the p-coumaric acid.

[9] Hydrogen bonds in proteins such as PYP take part in interrelated networks, where at the center of p-coumaric acid's phenolate O4 atom, there is an oxyanion hole that is crucial for photosensory function.

p -Coumaric acid exhibiting trans – cis isomerization due to absorption of light causing photochemical transitions. To the right demonstrates the molecular structure of p -coumaric acid in the ligand binding site and hydrogen bonding interactions involved in the innate oxyanion hole . To the left is a crystallographic image of p -coumaric acid in the ligand binding site based on PDB : 2PYP ​ PyMOL rendering. [ 9 ]