Functional Mechanism of the Photoactive Yellow Protein: A Transient Absorption Spectroscopy Perspective

Photoactive yellow protein (PYP) is a photoreceptor from extremophile bacteria Halorhodospira Halophila that swims out of blue light. PYP is supposed to be the responsible for the physiological action. Since the 3D structure of PYP resembles to the PAS domain proteins, PYP is proposed as a model system. The knowledge on how PYP responds to blue light- will shed light on the signal transduction mechanism of the PAS domain proteins. The excitation of blue light triggers the photocycle of PYP through an isomerization of para-coumaric acid chromophore with successive events of the protonation of chromophore, partial-unfolding of protein and resuming of initial state within the seconds of time scale. The partial unfolded state is supposed to be the signaling state. Here, the comprehensive results on the kinetics, dynamics and equilibria of these photocycle intermediates- recently discovered from the transient absorption measurements of the wild type and several key mutants- will be presented. PYP will continue to be the significant part of a newly introduced field of Optogenetics.