Ultrafast excited-state dynamics of chromophore-containing proteins.

摘要

Among the fastest events in biology are electron, energy, and proton transfer reactions. This thesis details ongoing studies of these reactions in model protein systems and explores the role of the surrounding protein matrix in mediating these reactions.; The Aequorea victoria green fluorescent protein (GFP) has become one of the most popular fluorescent indicators for protein localization and gene expression in cell and molecular biology research. The usefulness of GFP is enhanced by the availability of mutants with a broad range of absorption and emission maxima. Using fluorescence upconversion, the excited-state dynamics of some of these mutants (BFP, dual-emission GFPs, and YFP) are investigated. Pressure- and temperature-dependent studies shed light on the non-radiative decay pathways that compete with proton transfer in the excited state. The results provide insight into the factors that govern the ultimate usefulness of GFPs as fluorescent indicators.; Electrostatics affect virtually all aspects of protein structure and activity and are particularly important in proteins whose primary function is to stabilize charge. A fluorescent amino acid, Aladan, which can probe the electrostatic character of its surrounding environment, was introduced site-selectively at buried and exposed sites within the B I domain of protein G (GB1). Fluorescent upconversion and time-correlated photon counting techniques were used to monitor the dynamic Stokes shift of the probe molecule following femtosecond excitation. The results demonstrated differences in solvation dynamics measured at the surface and buried sites and were consistent with trends observed at steady state, suggesting that the interior of GB1 is polar and heterogeneous and that Aladan emission reflects the local dielectric response.; The photosynthetic reaction center (RC) is an ideal system for the study of electron and energy transfer. Despite a symmetrical arrangement of cofactors, unidirectional electron transfer occurs in wild-type RCs. The ultrafast, excited-state dynamics of wild-type and mutant RCs were investigated by fluorescence upconversion. The results suggest that the dominant source of functional asymmetry involves differences in the association of the functional- and non-functional-side chromophores with their environment (e.g. free and reorganization energy differences), rather than differences in electronic coupling.