Characterization and crystallization of a novel haemoglobinase from pathogenic Escherichia coli

A haemoglobin-degrading enzyme from pathogenic Escherichia coli has been cloned, expressed and purified to homogeneity. The pure protein proteolyses haemoglobin and binds haem. In vivo, its role is to remove haem from haemoglobin and pass it to the bacteria, allowing them to overcome the limiting concentration of iron available in the body. The protein has been crystallized using polyethylene glycol to give crystals in a hexagonal space group with unit-cell parameters a = b = 114.6, c = 434.3 A. X-ray data have been collected to 2.5 A resolution. This is the first member of the SPATE (serine protease autotransporters of Enterobacteriaceae) family of autotransporter proteins to be crystallized.