Chromophore–Protein Coupling beyond Nonpolarizable Models: Understanding Absorption in Green Fluorescent Protein

• DOI: 10.1021/acs.jctc.5b00650
• Publication Date: 2015-09-02T16:57:18Z
• Authors: Csaba Daday; Carles Curutchet; Adalgisa Sinicropi; Benedetta Mennucci; Claudia Filippi
• Keywords: Chromophore

The nature of the coupling photoexcited chromophore with environment in a prototypical system like green fluorescent protein (GFP) is to date not understood, and its description still defies state-of-the-art multiscale approaches. To identify which theoretical framework chromophore-protein complex can realistically capture essence, we employ here variety electronic-structure methods, namely, time-dependent density functional theory (TD-DFT), multireference perturbation (NEVPT2 CASPT2), quantum Monte Carlo (QMC) combination static point charges (QM/MM), DFT embedding (QM/DFT), classical polarizable through induced dipoles (QM/MMpol). Since structural modifications significantly affect photophysics GFP, also account for thermal fluctuations extensive molecular dynamics simulations. We find that treatment leads blue-shifted excitation energies including does cure coarseness MM description. While TDDFT calculations on large cluster models indicate need responsive protein, this response simply electrostatic: An improved ground state or via ground-state state-specific MMpol modify results obtained charges. Through use QM/MMpol linear formulation, different picture fact emerges main one transition corresponding dipoles. Such interaction significant red-shifts satisfactory agreement full QM at same level theory. Our findings demonstrate that, ultimately, faithfully capturing effects GFP requires regions but QM/classical model be useful approximation when extended beyond electrostatic-only formulation.