These results suggested that ASR could be a photochromic color sensor, whereas nothing was well-known about the structural changes and scheme of its photochromic reactions when we started the study.Figure 4.(Left) X-ray crystallographic structure of ASR (1XIO). Purple ribbons, green spheres, yellow and white sticks correspond to helices, water molecules, retinal and amino acid www.selleckchem.com/products/SB-203580.html residues, respectively. (Right) The Schiff base region of ASR and BR (translucent …Amino acid sequence comparison between ASR and BR reveals that some important residues for pumping protons are replaced in ASR. The proton donor to the Schiff base (Asp96 in BR) and one of proton release groups Inhibitors,Modulators,Libraries (Glu194 in BR) are replaced by serine residues, Ser86 and Ser188, respectively (Figure 5).Figure 5.
Comparison of amino acid sequences of ASR and BR. The transmembrane topology is based on the Inhibitors,Modulators,Libraries crystallographic three-dimensional structures. The sequence alignment was done using CLUSTAL W  with the default settings. Single letters in a circle denote …Ten amino acid residues out of twenty-five which constitute the retinal binding site are different from those of BR, probably accounting for the different absorption maximum and photochromic behavior of ASR. Among them, the most characteristic replacement is Pro206 located at the position of Asp212 in BR, which is one of the counterions of the Schiff base and a well conserved amino acid residue in archaeal type rhodopsins (Figure 6). The influence of Pro206 on the hydrogen bonds around the Schiff base should be studied precisely for elucidating the difference in the structural changes of retinal and protein between ASR and BR upon their activation.
Figure Inhibitors,Modulators,Libraries 6.The 25 amino acid sequence of archaeal-type rhodopsin around retinal. First, second, third, fourth and fifth categories represent the families of bacteriorhodopsin, halorhodopsin, sensory rhodopsin I, sensory rhodopsin II and other archaeal-type rhodopsins, …As shown above, ASR is a Inhibitors,Modulators,Libraries unique archaeal-type rhodopsin. However, the molecular properties, particularly the nature of its photochromic behavior, were Brefeldin_A much less known. Thus, in the last five years, we have studied various properties of ASR, mainly by use of spectroscopic techniques. Since ASR possesses visible absorption, UV-visible spectroscopy is the basic technique to study the properties of this molecule.
Low-temperature UV-visible spectroscopy was used to study the photochromism of ASR described in Section 4. In the photochromic reaction, the isomeric states of the retinal chromophore play an important role, and HPLC analysis is the direct method to determine the isomeric composition of the retinal chromophore. We used this method in the work described in Section www.selleckchem.com/products/Paclitaxel(Taxol).html 3. On the other hand, in our studies we have mostly used low-temperature Fourier-transform infrared (FTIR) spectroscopy [22,23].