title: Effect of protein environment on electronically excited and ionized states of the green fluorescent protein chromophore.
abstract: The effect of the protein environment on the electronic structure of the green fluorescent protein (GFP) chromophore is investigated by QM/MM (quantum mechanics/molecular mechanics) calculations. The protein has very small effect on the excitation energy of the bright absorbing and the lowest triplet states of the anionic GFP chromophore, deprotonated 4-hydroxybenzylidene-2,3-dimethylimidazolinone (HBDI) anion, however, it increases vertical detachment energy from 2.5 eV (gas-phase deprotonated HBDI anion) to 5.0 eV (solvated protein). We also investigated possible existence of the charge-transfer-to-solvent (CTTS) states associated with the GFP chromophore. Although precursors of such states appear in cluster calculations, a tightly packed structure of the protein prevents the formation of the CTTS states in this system. Motivated by a recently discovered new type of photoconversion, oxidative redding, we characterized the redox properties of GFP. The computed standard reduction potential of the anionic form of GFP is 0.47 V (for the GFP(•) + 1e → GFP(-) reaction), and the reduction potential at physiological conditions (pH 7, T = 25 °C) is 0.06 V.
authors: Department of Chemistry, University of Southern California, Los Angeles, California 90089-0482, United States.
authors: Ksenia B
authors: KB
authors: Bravaya
authors: Maria G
authors: MG
authors: Khrenova
authors: Bella L
authors: BL
authors: Grigorenko
authors: Alexander V
authors: AV
authors: Nemukhin
authors: Anna I
authors: AI
authors: Krylov