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.Metallocenters serve essential biological functions such as transferring electrons, stabilizing biomolecules, binding substrates, and catalyzing desirable reactions. Synthesis of these sites must be tightly controlled because simple competition between metals may lead to misincorporation with loss of function and because excess cytoplasmic concentrations of free metal ions can have toxic cellular effects. In many cases, cells have evolved elaborate metallocenter assembly systems that sequester metal cofactors from the cellular milieu, thus offering protection from adventitious reactions while ensuring the fidelity of metal insertion. In addition to maintaining metal homeostasis, these assembly systems facilitate protein conformational changes and active site modifications that are required for full enzymatic activity. Several metalloproteins have been investigated as models to understand the mechanisms and dynamics of active site assembly and the complex orchestrations of their metallocenter assembly systems. In this minireview, we discuss recent findings related to maturation of the nickel-containing enzyme urease.

A Bacillus paralicheniformis Iron-Containing Urease Reduces Urea Concentrations in Rice Wine

“…In addition, a multiple-sequence alignment of BpUreC with other UreC proteins, including the iron-containing HmUreC2 (Fig. 1B), confirmed that all the amino acids involved in nickel binding (His137, His139, Lys220, His247, His275, and Asp363) and catalysis (His222 and His323) are highly conserved (3,4,31,32). The Gly280, Cys322, Arg339, and Ala366 residues, which are thought to be important for the catalytic mechanism, but not for metal binding, are also strictly conserved (32).…”

“…UreE, a metallochaperone, delivers nickel to urease apoprotein via the chaperone complex (UreD-UreF-UreG) 3 , in which UreD functions as a scaffold for the recruitment of other accessory subunits, UreF guarantees metallocenter fidelity, and UreG is a GTPase for the incorporation of nickel ions (3,4,(19)(20)(21). Although the ureD gene in Helicobacter species (18) was renamed ureH, its function is consistent with that of other UreD accessory proteins.…”

“…and H 2 N-COOH ϩ H 2 O ¡ H 2 CO 3 ϩ NH 3 ), have been found in plants and many microorganisms (1)(2)(3)(4)(5). Because of their multifaceted contributions to the environmental cycling of nitrogen and localized neutralization of pH (1,6,7), ureases have always attracted intensive attention.…”

“…To understand the activation mechanisms of ureases and the roles of accessory proteins in the posttranslational modifications of ureases, many different microbial nickel-containing ureases have been identified and characterized. Although the structural subunits and enzyme active sites have been well studied (3)(4)(5)(10)(11)(12)(13)(14)(15), the function of each accessory protein and the urease maturation mechanism are still poorly understood (3,4,(16)(17)(18)(19)(20).…”

“…In most of the microbial ureases identified, the accessory proteins (UreE, UreD, UreG, and UreF) are essential for active-site metalation and urease maturation (3,4,20). UreE, a metallochaperone, delivers nickel to urease apoprotein via the chaperone complex (UreD-UreF-UreG) 3 , in which UreD functions as a scaffold for the recruitment of other accessory subunits, UreF guarantees metallocenter fidelity, and UreG is a GTPase for the incorporation of nickel ions (3,4,(19)(20)(21).…”