Spectroscopic and Structural Analysis of Cu2+-Induced Fluorescence Quenching of ZsYellow
Division of Biotechnology, College of Life Sciences and Biotechnology, Korea University, Seoul 02841, Korea
Department of Bioengineering, College of Life Science, Dalian Minzu University, Dalian 116600, China
Key Laboratory of Biotechnology and Bioresources Utilization of Ministry of Education, Dalian Minzu University, Dalian 116024, China
Department of Life Science, Pohang University of Science and Technology, Pohang 37673, Korea
Author to whom correspondence should be addressed.
Present address: Department of Biotechnology and Enzyme Catalysis, Institute of Biochemistry, University of Greifswald, 17487 Greifswald, Germany.
Biosensors 2020, 10(3), 29; https://doi.org/10.3390/bios10030029
Received: 25 February 2020 / Revised: 17 March 2020 / Accepted: 19 March 2020 / Published: 23 March 2020
Fluorescent proteins exhibit fluorescence quenching by specific transition metals, suggesting their potential as fluorescent protein-based metal biosensors. Each fluorescent protein exhibits unique spectroscopic properties and mechanisms for fluorescence quenching by metals. Therefore, the metal-induced fluorescence quenching analysis of various new fluorescent proteins would be important step towards the development of such fluorescent protein-based metal biosensors. Here, we first report the spectroscopic and structural analysis of the yellow fluorescent protein ZsYellow, following its metal-induced quenching. Spectroscopic analysis showed that ZsYellow exhibited a high degree of fluorescence quenching by Cu2+. During Cu2+-induced ZsYellow quenching, fluorescence emission was recovered by adding EDTA. The crystal structure of ZsYellow soaked in Cu2+ solution was determined at a 2.6 Å resolution. The electron density map did not indicate the presence of Cu2+ around the chromophore or the β-barrel surface, which resulted in fluorescence quenching without Cu2+ binding to specific site in ZsYellow. Based on these results, we propose the fluorescence quenching to occur in a distance-dependent manner between the metal and the fluorescent protein, when these components get to a closer vicinity at higher metal concentrations. Our results provide useful insights for future development of fluorescent protein-based metal biosensors.