Molecular structure and nickel-binding capacity of Proteus mirabilis UreE

UreE is a nickel chaperone that is required for the safe and efficient delivery of nickel to the active site of the metalloenzyme urease, which is a key virulence factor of the urinary-tract pathogen Proteus mirabilis. We investigated the structural features of P. mirabilis UreE (PmUreE) using protein X-ray crystallography and its nickel-binding capacity by inductively coupled plasma mass spectrometry. Here, we report a 2.0 Å resolution crystal structure of homodimeric PmUreE and show that it has the capacity to bind five Ni(II) ions per dimer. Truncation of the histidine-rich C-terminus reduced the nickel-binding capacity by two Ni(II) ions per dimer, and comparison with homologous UreE structures allowed the assignment of putative nickel-binding sites within the PmUreE structure. These findings increase our understanding of how PmUreE binds nickel and ultimately prevents this toxic metal from causing significant cellular damage in P. mirabilis.