Overexpression, purification, crystallization, and preliminary X-ray characterization of a methionine sulfoxide reductase AB from Helicobacter pylori

The main function of methionine sulfoxide reductases (Msr) in many organisms is to protect cells against oxidative stress caused by the catalyzed reduction of oxidized methionine to normal methionine. In a few micro-organisms, the existence of Msr as a fusion protein on a single polypeptide, MsrAB, was reported. However, Msr generally exists as separate enzymes MsrA and MsrB. Here, MsrAB from Helicobacter pylori (HpMsrAB) was overexpressed in Escherichia coli, purified, and crystallized to determine its structure. HpMsrAB X-ray diffraction data were collected to the resolution of 3.3 Å, and the crystals were found to belong to the tetragonal space group P4₁2₁2, with the unit cell parameters a =100.91, b =100.91, and c =160.08 Å. The crystals corresponded to 5.38 ų Da^-1 of Matthews coefficient and 77.2% solvent content from the molecular replacement suggest that there is a single molecule in an asymmetric unit. Due to their unusually high solvent content, diffraction of these crystals only reach a resolution of 3.3 Å. A preliminary solution was determined by molecular replacement. Further refinement of the structure is in progress.