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 ( XpsEN), are reported. XpsEN has been crystallized at 277 K using PEG 400 as precipitant. These crystals belong to the tetragonal space group P4(1)2(1)2 ( or P4(3)2(1)2), with unit- cell parameters a = b = 56.1, c = 102.7 Angstrom. A 98.5% complete native data set from a frozen crystal has been collected to 2.0 Angstrom resolution at 100 K with an overall R-merge of 5.0%. The presence of one subunit of XpsEN per asymmetric unit gives a crystal volume per protein weight (V-M) of 1.92 Angstrom(3) Da(-1) and a solvent content of 36.1%.