Preliminary X-ray analysis of XC5848, a hypothetical ORFan protein with an Sm-like motif from Xanthomonas campestris.

XC5848, a hypothetical protein from the pathogenic bacterium Xanthomonas campestris that causes black rot, has been chosen as a potential target for the discovery of novel folds. It is unique to the Xanthomonas genus and has significant sequence identity mainly to corresponding proteins from the Xanthomonas genus. In this paper, the cloning, overexpression, purification and crystallization of the XC5848 protein are reported. The XC5848 crystals diffracted to a resolution of at least 1.68 A. They belong to the orthorhombic space group P2(1)2(1)2(1), with unit-cell parameters a = 48.13, b = 51.62, c = 82.32 A. Two molecules were found in each asymmetric unit. Preliminary structural studies nevertheless indicate that XC5848 belongs to the highly conserved Sm-like alpha-beta-beta-beta-beta fold. However, significant differences in sequence and structure were observed. It therefore represents a novel variant of the crucial Sm-like motif that is heavily involved in mRNA splicing and degradation.