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Crystallization and preliminary X-ray structure determination of jack bean urease with a bound antibody fragment.

Urease allows organisms to use exogenous and internally generated urea as a nitrogen source, by catalyzing the hydrolysis of urea to form ammonia and carbon dioxide. Urease may also participate in the systemic nitrogen-transport pathways and possibly acts as a toxic defence protein. Jack bean urease (JBU) was the first nickel-metalloenzyme identified and was crystallized as early as 1926. Despite this, the structure has not yet been determined. An antibody fragment, Fv, that has a high affinity for JBU has been used to aid crystallization. The complex, which retains full enzyme activity, forms very small crystals that diffract weakly to 3.3 A. The crystals belong to the rhombohedral space group R32, with unit-cell parameters a = b = 228.6, c = 130.9 A. The structure of the urease molecule has been solved by molecular replacement using the structure of homogenous enzyme from Klebsiella aerogenes as a search model.