کد مقاله | کد نشریه | سال انتشار | مقاله انگلیسی | نسخه تمام متن |
---|---|---|---|---|
5371167 | 1503938 | 2013 | 7 صفحه PDF | دانلود رایگان |
![عکس صفحه اول مقاله: Thermodynamic parameters of anion binding to halorhodopsin from Natronomonas pharaonis by isothermal titration calorimetry Thermodynamic parameters of anion binding to halorhodopsin from Natronomonas pharaonis by isothermal titration calorimetry](/preview/png/5371167.png)
Halorhodopsin (HR), an inwardly directed, light-driven anion pump, is a membrane protein in halobacterial cells that contains the chromophore retinal, which binds to a specific lysine residue forming the Schiff base. An anion binds to the extracellular binding site near the Schiff base, and illumination makes this anion go to the intracellular channel, followed by its release from the protein and re-uptake from the opposite side. The thermodynamic properties of the anion binding in the dark, which have not been previously estimated, are determined using isothermal titration calorimetry (ITC). For Clâ as a typical substrate of HR from Natronomonas pharaonis, ÎG = âRT ln(1/Kd) = â 15.9 kJ/mol, ÎH = â 21.3 kJ/mol and TÎS = â 5.4 kJ/mol at 35 °C, where Kd represents the dissociation constant. In the dark, Kd values have been determined by the usual spectroscopic methods and are in agreement with the values estimated by ITC here. Opsin showed no Clâ binding ability, and the deprotonated Schiff base showed weak binding affinity, suggesting the importance of the positively charged protonated Schiff base for the anion binding.
Highlights⺠The thermodynamic parameters of anion binding to halorhodopsin were determined. ⺠The dilution heat was minimalized by considering water activities. ⺠Kd values were almost equal to those determined by the conventional spectroscopy. ⺠The protonated Schiff base was essential for the anion binding.
Journal: Biophysical Chemistry - Volume 172, February 2013, Pages 61-67