The Measurement Of H-C-C-H Torsional Angle Of The Retinal Ligand In Bacteriorhodopsin

Bacteriorhodopsin(bR) is the crucial membrane protein generated by the Halobacterium salinarum, contains seven helices linked by loops on both sides of the cell membranes, with twenty-six kDa. It functions as proton pump, electronic charge separation and photochromic. Each bR contains one molecule retinal which covalently linked to Lys216as a schiff base. After illumination, the retinal chromophore will transfer the optical energy to Chemical energy in order to initiate the proton transfer. During the vectorial transport from cytoplasm to extracellular region of the proton, the retinal appears cascade photoisomerism and plays a sole role. Different crystal lographic structures show that:the energy promoting the proton transfer conserved in the distorted single bond and in twists of two double bonds in the conjugate segment of the retinal.Solid State NMR (SSNMR) is one of the powerful methods focusing mainly on solid samples. SSNMR has signature strength in the area such as transmembrane proteins, large proteins (>30kDa) and amyloid peptide fibrils, which cannot be crystallized or dissolved easily. For the biosamples, using specific ssNMR methods can detect the precise structure of a certain fragment. NMR technique can only detect those nuclei that their spin number is not zero, while the natural abundance nuclei of carbon is zero. Therefore we have to using I3C labeled samples in the experiments.In our project, we using [14,15-13C2]-retinal as our sample, choosing ssNMR technique the2Q-HLF method, research the torsional angel of H-14C-15C-H segment, which is just approached to the N nuclei of Schiff base. The double quantum coherence of the two neighbored13C2spin pair is excited by C7squence, evolution under the FSLG decoupling sequence in variable increment time. We can acquire the geometry of the13C2pair with their bonded H nuclei from the coherence evolutions under the local fields providing by their bonded H nuclei, that is the torsional angle. Our work may offer some experimental evidence to the study of bR and its photocycle and proton pump function from atom level.