Preliminary diffraction analysis of Salmonella Typhi YfdX crystallized in the dimeric state under high pH conditions

Abstract

YfdX is a bacterial protein that has been identified in a number of gram-negative species, including Salmonella enterica serovar Typhi, which is the causative agent of typhoid fever. Previously, we reported the pH-dependent change of the oligomeric state of S. Typhi YfdX between tetrameric (at pH 5.5) and dimeric (at pH 8.0) forms, which was demonstrated by size exclusion chromatography-multiangle light scattering and small angle X-ray scattering. However, only the threedimensional structure of tetrameric YfdX determined using crystals obtained under low pH conditions was presented in our previous study. In this study, in an effort to obtain structural information for YfdX in the dimeric state at high pH, wildtype and Sel-Met-substituted recombinant S. Typhi YfdX proteins were produced in an Escherichia coli expression system, purified using Ni-NTA affinity chromatography and size exclusion chromatography, and crystallized. Crystals obtained at high pH were selected for further optimization to determine the crystal structure of dimeric YfdX. X-ray diffraction data were collected at resolutions of 1.70 A and 1.90 A for native and Sel-Met-substituted crystals, respectively. A preliminary diffraction analysis was conducted, which indicated that our crystals commonly belong to the P2 space group, with six YfdX molecules present in the single asymmetric unit.