First-principles study of one and two-photon absorption of an artificial fluorescent protein chromophore by 5-hydroxytryptophan substitution

Chromophore of fluorescent proteins not only has a simple structure, but also plays a crucial role on their optical properties. Many fluorescent proteins with novel optical properties have been engineering by manipulating the aminoacids sequence of chromophore. In this Letter, we firstly designed a 5-hydroxytryptophan (5-HTP) by replacing the aromatic amino acids of chromophores with non-natural amino acid of 5-HTP. By employing the time-dependent-density-functional theory combining with sum-over-states method, one-photon absorption (OPA) and two-photon absorption (TPA) of 5-HTP were studied. Comparing with original chromophores, 5-HTP replacement could result in red-shift of OPA spectra and improvement of TPA characters.