Structure-function-dynamics relationships in the peculiar Planktothrix PCC7805 OCP1: impact of his-tagging and carotenoid type

The orange carotenoid protein (OCP) is a photoactive protein involved in cyanobacterial photoprotection. Here, we report on the functional, spectral and structural characteristics of the peculiar Planktothrix PCC7805 OCP (Plankto-OCP). We show that this OCP variant is characterized by higher photoactivation and recovery rates, and a stronger energy-quenching activity, compared to other OCPs studied thus far. We characterize the effect of the functionalizing carotenoid and of his-tagging on these reactions, and the time scales on which these modifications affect photoactivation. The presence of a His-tag at the C-terminus has a large influence on photoactivation, thermal recovery and PBS-fluorescence quenching, and likewise for the nature of the carotenoid that additionally affects the yield and characteristics of excited states and the ns-s dynamics of photoactivated OCP. By solving the structures of Plankto-OCP in the ECN- and CAN-functionalized states, each in two closely-related crystal forms, we further unveil the molecular breathing motions that animate Plankto-OCP at the monomer and dimer levels. We finally discuss the structural changes that could explain the peculiar properties of Plankto-OCP. - Complete functional characterization of Synechocystis and Planktothrix OCPs - Hitherto unknown structures of ECN- and CAN-functionalized Planktothrix OC

Femtosecond studies of orientational anisotropy decay of benzopyranthione in the excited S2 state in hydrocarbons

Reorientational dynamics of 4H-1-benzopyrane-4-thione (BPT) in the S2 state, in hydrocarbon solution, is studied from the anisotropy decay of fluorescence upconversion and pump–probe absorption transients with femtosecond time resolution. The anisotropy decay is found to be monoexponential in n-hexane, n-heptane, n-octane, n-decane, n-dodecane and cyclohexane. The dependence of the rotational time constant, τor, on the solvent viscosity is approximated by a linear function with a slope of 2.6 ± 1 ps/cP indicating slip conditions. The decay of orientational anisotropy is observed for the first time for a molecule in the S2 state

Direct observation of 1,2-hydrogen migration in the excited states of alkyl diazo esters by ultrafast time resolved IR spectroscopy

The mechanism of 1,2-H migration process in photoexcited alkyl diazo esters was studied by femtosecond IR transient absorption spectroscopy and theoretical calculations. Two possible processes are discussed: rearrangement in the diazo excited state (RIES) and the intermediacy of singlet carbene species. In chloroform solvent ulrafast IR data show a subpicosecond rise of alkene species indicating the occurrence of the RIES process. Failure in carbene species detection is explained by their absence or very low quantum yield of formation

Femtosecond fluorescence up-conversion and transient absorption studies of the S2 state in the hydrogen-bonded benzopyranthione-water complex

We have studied for the first time the photophysics of the thioketone, 4H-1-benzopyrane-4-thione (BPT), in water and deuterated water, by using femtosecond fluorescence up-conversion and transient absorption spectroscopies. We propose that the S2-state deactivation occurs in the hydrogen-bonded BPT–water complex. The lifetime of the complex in the S2 state is found to be as short as 1.0 ± 0.1 ps in H2O, and 2.2 ± 0.1 ps in D2O