The structure of urease activation complexes examined by flexibility analysis, mutagenesis, and small-angle X-ray scattering.

Conformational changes of Klebsiella aerogenes urease apoprotein (UreABC)(3) induced upon binding of the UreD and UreF accessory proteins were examined by a combination of flexibility analysis, mutagenesis, and small-angle X-ray scattering (SAXS). ProFlex analysis of urease provided evidence that the major domain of UreB can move in a hinge-like motion to account for prior chemical cross-linking results. Rigidification of the UreB hinge region, accomplished through a G11P mutation, reduced the extent of urease activation, in part by decreasing the nickel content of the mutant enzyme, and by sequestering a portion of the urease apoprotein in a novel activation complex that includes all of the accessory proteins. SAXS analyses of urease, (UreABC-UreD)(3), and (UreABC-UreDF)(3) confirm that UreD and UreF bind near UreB at the periphery of the (UreAC)(3) structure. This study supports an activation model in which a domain-shifted UreB conformation in (UreABC-UreDF)(3) allows CO(2) and nickel ions to gain access to the nascent active site.