Effect of tryptophan mutation on the structure of LOV1 domain of phototropin1 protein of Ostreococcus tauri: A combined molecular dynamics simulation and biophysical approach.

Background: Light, oxygen and voltage (LOV) proteins detect blue light by formation of a covalent 'photoadduct' between the flavin chromophore and the neighboring conserved cysteine residue. LOV proteins devoid of this conserved photoactive cysteine are unable to form this 'photoadduct' upon light illumination, but they can still elicit functional response via the formation of neutral flavin radical. Recently, tryptophan residue has been shown to be the primary electron donors to the flavin excited state.

Methods: Photoactive cysteine (Cys42) and tryptophan (Trp68) residues in the LOV1 domain of phototropin1 of Ostreococcus tauri (OtLOV1) was mutated to alanine and threonine respectively. Effect of these mutations have been studied using molecular dynamics simulation and spectroscopic techniques.

Results: Molecular dynamics simulation indicated that W68T did not affect the structure of OtLOV1 protein, but C42A leads to some structural changes. An increase in the fluorescence lifetime and quantum yield values was observed for the Trp68 mutant.

Conclusions: An increase in the fluorescence lifetime and quantum yield of Trp68 mutant compared to the wild type protein suggests that Trp68 residue participates in quenching of the flavin excited state followed by photoexcitation.

General Significance: Enhanced photo-physical properties of Trp68 OtLOV1 mutant might enable its use for the optogenetic and microscopic applications.