Crystallization and preliminary X-ray crystallographic analysis of the N-terminal domain of XpsE protein from Xanthomonas campestris, an essential component of the type II protein-secretion machinery

Secretion of pre-folded extracellular proteins across the outer membrane of Gram-negative bacteria is mainly assisted by the type II secretion machinery composed of 12-15 proteins. Here, the crystallization and preliminary analysis of one of the essential components of Xanthomonas campestris secretion machinery, the 21 kDa N-terminal domain of XpsE protein (XpsE_N), are reported. XpsE_N has been crystallized at 277 K using PEG 400 as precipitant. These crystals belong to the tetragonal space group P4₁2₁2 (or P4₃2₁2), with unit-cell parameters a = b = 56.1, c = 102.7 Å. A 98.5% complete native data set from a frozen crystal has been collected to 2.0 Å resolution at 100 K with an overall R_merge of 5.0%. The presence of one subunit of XpsE_N per asymmetric unit gives a crystal volume per protein weight (V_M) of 1.92 Å³ Da^-1 and a solvent content of 36.1%.