No abstract

Arginyl-tRNA synthetase (ArgRS) recognizes two major identity elements of tRNA Arg : A20, located at the outside corner of the L-shaped tRNA, and C35, the second letter of the anticodon. Only a few exceptional organisms, such as the yeast Saccharomyces cerevisiae, lack A20 in tRNA Arg . In the present study, we solved the crystal structure of a typical A20-recognizing ArgRS from Thermus thermophilus at 2.3 Å resolution. The structure of the T. thermophilus ArgRS was found to be similar to that of the previously reported

Cell-free expression has become a highly promising tool for the efficient production of membrane proteins. In this study, we used a dialysis-based Escherichia coli cell-free system for the production of a membrane protein actively integrated into liposomes. The membrane protein was the light-driven proton pump bacteriorhodopsin, consisting of seven transmembrane a-helices. The cell-free expression system in the dialysis mode was supplemented with a combination of a detergent and a natural lipid, phosphatidylcholine from egg yolk, in only the reaction mixture. By examining a variety of detergents, we found that the combination of a steroid detergent (digitonin, cholate, or CHAPS) and egg phosphatidylcholine yielded a large amount (0.3-0.7 mg/mL reaction mixture) of the fully functional bacteriorhodopsin. We also analyzed the process of functional expression in our system. The synthesized polypeptide was well protected from aggregation by the detergent-lipid mixed micelles and/or lipid disks, and was integrated into liposomes upon detergent removal by dialysis. This approach might be useful for the high yield production of functional membrane proteins.