Cation Specific Effects on the Domain-Domain Interaction of Heterogeneous Dimeric Protein Revealed by FRET Analysis
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ORIGINAL ARTICLE
Cation Specific Effects on the Domain-Domain Interaction of Heterogeneous Dimeric Protein Revealed by FRET Analysis Tomohiro Aoyama 1 & Akane Kato 1 & Etsuko Nishimoto 1 Received: 16 March 2020 / Accepted: 11 May 2020 # Springer Science+Business Media, LLC, part of Springer Nature 2020
Abstract Specific monovalent cation effects on the domain-domain interaction of heterogeneous dimeric protein were investigated using green fluorescent protein (GFP)-glutathione-s-transferase (GST) fusion protein as a model protein. Conjugating N-terminal of GST domain with a fluorescence probe Cyanine3, complementary increase and decrease of fluorescence intensities of Cyanine3 and GFP were recognized on the exclusive excitation of GFP and further the fluorescence decay of GFP was remarkably accelerated to show that an excellent Förster type of resonance excitation energy transfer (FRET) pair was constructed between GFP- and GST-domain. The spectral overlap integral and critical distance of the FRET pair were estimated to be 5.96×1013 M−1cm3 and 62.5 Å, respectively. The FRET rate and efficiency evaluated by fluorescence lifetime of the energy donor, GFP, were influenced by the monovalent cations included in the buffer solution to suggest that the domain-domain interactions of GFPGST fusion protein would be susceptible to cation species and their concentrations. The order affecting the domain-domain interaction was estimated to be Li+>NH4+ >Na+>K+>Cs+, almost corresponding to the reverse Hofmeister series. Keywords Specific cation effect, Hofmeister series, Domain-domain interaction, GFP-GST fusion protein, FRET, Fluorescence anisotropy decay
Introduction Many protein scientists try to design first optimum buffer systems on the start of their research. They empirically realize anions and/or cations specifically give decisive influences on the characteristics of protein. Indeed, some proteins and enzymes require peculiar ion species to keep the structural stability or to complete the superior activity, respectively. In aqueous solutions, ion species independently give specific effects on the viscosity, surface tension, density, and boiling and freezing points of the solution [1]. Moreover, co-existing with proteins, stability of protein [2–7], enzyme activity [8–13], protein-protein interaction [14], protein crystallization [15], and multiplication of microorganism [16] are also subjected to the ion specific effect.
* Etsuko Nishimoto [email protected] 1
Institute of Biophysical Chemistry, Faculty of Agriculture, Graduate School of Kyushu University, 744 Motooka, Nishi-ku, Fukuoka 819-0395, Japan
The ion specificity on protein systems were reported first by Hofmeister in 1888 [17]. He found that each ion precipitates eggwhite proteins under its own concentrations and determined the precipitation order by salting out. This order is known today as Hofmeister series. In the case of anion, the efficiency of the salting out he decided was higher in the order of SO42− > HPO42− > F− > CH3COO− > Cl− > Br− > NO3−
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