4MYN: Crystal Structure Of Trypanosoma Cruzi Formiminoglutamase N114h Variant With Mn2+2

The crystal structure of formiminoglutamase from Trypanosoma cruzi (TcFIGase) is reported at 1.85 A resolution. Although the structure of this enzyme was previously determined by the Structural Genomics of Pathogenic Protozoa Consortium (PDB accession code 2A0M), this structure was determined at low pH and lacked bound metal ions; accordingly, the protein was simply annotated as "arginase superfamily protein" with undetermined function. We show that reconstitution of this protein with Mn(2)(+) confers maximal catalytic activity in the hydrolysis of formiminoglutamate to yield glutamate and formamide, thereby demonstrating that this protein is a metal-dependent formiminoglutamase. Equilibration of TcFIGase crystals with MnCl(2) at higher pH yields a binuclear manganese cluster similar to that observed in arginase, except that the histidine ligand to the Mn(2)(+)(A) ion of arginase is an asparagine ligand (N114) to the Mn(2)(+)(A) ion of TcFIGase. The crystal structure of N114H TcFIGase reveals a binuclear manganese cluster essentially identical to that of arginase, but the mutant exhibits a modest 35% loss of catalytic efficiency (k(cat)/K(M)). Interestingly, when TcFIGase is prepared and crystallized in the absence of reducing agents at low pH, a disulfide linkage forms between C35 and C242 in the active site. When reconstituted with Mn(2)(+) at higher pH, this oxidized enzyme exhibits a modest 33% loss of catalytic efficiency. Structure determinations of the metal-free and metal-bound forms of oxidized TcFIGase reveal that although disulfide formation constricts the main entrance to the active site, other structural changes open alternative channels to the active site that may help sustain catalytic activity.
PDB ID: 4MYNDownload
MMDB ID: 115541
PDB Deposition Date: 2013/9/27
Updated in MMDB: 2013/11
Experimental Method:
x-ray diffraction
Resolution: 1.8  Å
Source Organism:
Similar Structures:
Biological Unit for 4MYN: trimeric; determined by author and by software (PISA)
Molecular Components in 4MYN
Label Count Molecule
Proteins (3 molecules)
Molecule annotation
Chemicals (6 molecules)
* Click molecule labels to explore molecular sequence information.

Citing MMDB