Di- and oligopeptide- binding protein OppAs play important roles in solute and nutrient uptake, sporulation, biofilm formation, cell wall muropeptides recycling, peptide-dependent quorum-sensing responses, adherence to host cells, and a variety of other biological processes. Soluble OppA from Thermoanaerobacter tengcongensis was expressed in Escherichia coli. The protein was found to be >95% pure with SDS-PAGE after a series of purification steps and the purity was further verified by mass spectrometry. The protein was crystallized using the sitting-drop vapour-diffusion method with PEG 400 as the precipitant. Crystal diffraction extended to 2.25 angstrom. The crystal belonged to space group C222(1), with unit-cell parameters of a = 69.395, b = 199.572, c = 131.673 angstrom, and alpha = beta = gamma = 90 degrees. (C) 2012 Elsevier Inc. All rights reserved.