Putative thioredoxin Trx1 from Thermosipho africanus strain TCF52B: expression, purification and structural determination using S-SAD

Thioredoxin is a small ubiquitous protein that plays a role in many biological processes. A putative thioredoxin, Trx1, from Thermosipho africanus strain TCF52B, which has low sequence identity to its closest homologues, was successfully cloned, overexpressed and purified. The protein was crystallized using the microbatch-under-oil technique at 289 K in a variety of conditions; crystals grown in 0.2 M MgCl2, 0.1 M bis-tris pH 6.5, 25%(w/v) PEG 3350, which grew as irregular trapezoids to maximum dimensions of 1.2 x 1.5 x 0.80 mm, were used for sulfur single-wavelength anomalous dispersion analysis. The anomalous sulfur signal could be detected to 2.83 angstrom resolution using synchrotron radiation on the 08B1-1 beamline at the Canadian Light Source. The crystals belonged to space group P2(1)2(1)2(1), with unit-cell parameters a = 40.6, b = 41.5, c = 56.4 angstrom, alpha = beta = gamma = 90.0 degrees.