Biosynthesis of the urease metallocenter

Abstract

Metalloenzymes often require elaborate metallocenter assembly systems to create functional active sites. The medically important dinuclear nickel enzyme urease provides an excellent model for studying metallocenter assembly. Nickel is inserted into the urease active site in a GTP-dependent process with the assistance of UreD/UreH, UreE, UreF, and UreG. These accessory proteins orchestrate apoprotein activation by delivering the appropriate metal, facilitating protein conformational changes, and possibly providing a requisite post-translational modification. The activation mechanism and roles of each accessory protein in urease maturation are the subject of ongoing studies, with the latest findings presented in this minireview.

Keywords: Biosynthesis; Chaperone Chaperonin; GTPase; Metalloenzymes; Nickel; Urease.

FIGURE 1.

Urease structures. A, three-subunit bacterial ureases (UreA, red; UreB, blue; UreC, green; with two more copies, yellow) assemble into a trimer of trimers (Protein Data Bank code 1FWJ). B, two-subunit Helicobacter ureases (a fusion of the two small domains, blue; large subunit, green; with two more copies, yellow) form a trimer of dimers, which interacts with three more trimers (gray surface view) to form a dodecamer of dimers (code 1E9Z). C, single-subunit urease of fungi and plants (a fusion of all three domains, green; with two more copies, yellow) forms a trimer that stacks back-to-back with a second trimer (gray surface view) (code 3LA4). D, dinuclear Ni²⁺ metallocenter of urease (Ni²⁺, magenta; solvent, red).

FIGURE 2.

Structure of UreH:UreF:UreG. Shown are two views of the (UreH:UreF:UreG)₂ complex from H. pylori (UreH, UreF, and UreG in shades of yellow, gray, and magenta, respectively). A GDP molecule (cyan) is located in each UreG.

FIGURE 3.

Model of K. aerogenes urease activation. The trimer-of-trimers urease apoprotein (UreA, red; UreB, blue; UreC, green) either sequentially binds UreD (yellow), UreF (gray), and UreG (magenta) or binds the UreDFG complex (only one protomer of each protein is shown, but the isolated complex contains two protomers of each). Formation of the active enzyme requires CO₂ to carbamylate Lys-217 at the native active site, GTP binding to and hydrolysis by UreG, and nickel delivery by dimeric UreE (cyan). It remains unclear whether the accessory proteins are released as a UreDFG unit or as individual proteins.