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Excited states of the green fluorescent protein chromophore: Performance of ab initio and semi-empirical methods

Authors

  • Marius Wanko,

    1. Nano-Bio Spectroscopy Group and ETSF Scientific Development Centre, Departamento de Física de Materiales, Universidad del País Vasco, Centro de Física de Materiales CSIC-UPV/EHU-MPC and DIPC Avenida de Tolosa 72, 20018 San Sebastián, Spain
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  • Pablo García-Risueño,

    1. Instituto de Química Física Rocasolano, CSIC, C/Serrano 119, 28006 Madrid, Spain
    2. BIFI/Departamento de Física Teórica, Universidad de Zaragoza, C/Cerbuna 12, 50009 Zaragoza, Spain
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  • Angel Rubio

    Corresponding author
    1. Nano-Bio Spectroscopy Group and ETSF Scientific Development Centre, Departamento de Física de Materiales, Universidad del País Vasco, Centro de Física de Materiales CSIC-UPV/EHU-MPC and DIPC Avenida de Tolosa 72, 20018 San Sebastián, Spain
    • Phone: +34 94301 8292, Fax: +34 94301 8390
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  • Dedicated to Thomas Frauenheim on the occasion of his 60th birthday

Abstract

The complex photophysical properties of fluorescent proteins give rise to a wide field of applications as markers in molecular biology. Understanding these properties is essential for rational genetic engineering of new fluorescent proteins. Here, theoretical models are required to support the interpretation of structural and spectroscopic experimental data. This requires the accurate and reliable prediction of excited-state features of the chromophore and its interactions with the protein matrix. Here, we compare calculations of absorption and emission energies of semi-empirical (OM2/MRCI, ZINDO/S, and TD-DFTB) and ab initio (SORCI, CC2, and TDDFT) approaches for the HBDI chromophore in vacuo and wild-type green fluorescent protein (GFP) using QM/MM models. We discuss the influence of electrostatic fields, the chromophore geometry, the size of the QM region, and methodological aspects, in particular charge-transfer states in TDDFT and the applicability of real-space TDDFT codes. We revisit previous opposing theoretical studies and benchmark gas-phase measurements.

original image

Proton transfer wire of wild-type green fluorescent protein (wt-GFP).

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