Refolding, crystallization and preliminary X-ray crystallographic studies of the β-barrel domain of BamA, a membrane protein essential for outer membrane protein biogenesis

In Gram-negative bacteria, the assembly of outer membrane proteins (OMPs) requires a five-protein β-barrel assembly machinery (BAM) complex, of which BamA is an essential and evolutionarily conserved integral outer membrane protein. Here, the refolding, crystallization and preliminary X-ray crystallo­graphic characterization of the β-barrel domain of BamA from Escherichia coli (EcBamA) are reported. Native and selenomethionine-substituted EcBamA proteins were crystallized at 16°C and X-ray diffraction data were collected to 2.6 and 3.7 Å resolution, respectively. The native crystals belonged to space group P2₁2₁2, with unit-cell parameters a = 118.492, b = 159.883, c = 56.000 Å and two molecules in one asymmetric unit; selenomethionine-substituted protein crystals belonged to space group P4₃22, with unit-cell parameters a = b = 163.162, c = 46.388 Å and one molecule in one asymmetric unit. Initial phases for EcBamA β-barrel domain were obtained from a SeMet SAD data set. These preliminary X-ray crystallographic studies paved the way for further structural determination of the β-barrel domain of EcBamA.