Methionine sulfoxide reductase (Msr) is a repair enzyme that reduces oxidized methionine to methionine. The Msr enzyme is divided into MsrA and MsrB, which reduce the S and R configurations of the substrate, respectively. In some pathogenic bacteria MsrA and MsrB exist
in a fusion‐protein form, MsrAB. In this study, the recombinant MsrA part of MsrAB from Haemophilus influenzae (HIMsrA) was overexpressed, purified and crystallized using the hanging‐drop vapour‐diffusion method. A diffraction data set was collected to 1.6 Å
resolution. The crystal of HIMsrA was found to belong to space group P41212, with unit‐cell parameters a = b = 57.29, c = 186.28 Å, a calculated Matthews coefficient of 1.82 Å3 Da−1
and two molecules per asymmetric unit. A preliminary solution was determined by molecular replacement. Refinement of the structure is currently in progress.