4MAB: Resolving Cys to Ala variant of Salmonella Alkyl Hydroperoxide Reductase C in its substrate-ready conformation

To reduce peroxides, peroxiredoxins (Prxs) require a key "peroxidatic" Cys that, in a substrate-ready fully folded (FF) conformation, is oxidized to sulfenic acid and then, after a local unfolding (LU) of the active site, forms a disulfide bond with a second "resolving" Cys. For Salmonella typhimurium alkyl hydroperoxide reductase C (StAhpC) and some other Prxs, the FF structure is only known for a peroxidatic Cys-->Ser variant, which may not accurately represent the wild-type enzyme. Here, we obtain the structure of authentic reduced wild-type StAhpC by dithiothreitol treatment of disulfide form crystals that fortuitously accommodate both the LU and FF conformations. The unique environment of one molecule in the crystal reveals a thermodynamic linkage between the folding of the active site loop and C-terminal regions, and comparisons with the Ser variant show structural and mobility differences from which we infer that the Cys-->Ser mutation stabilizes the FF active site. A structure for the C165A variant (a resolving Cys to Ala mutant) in the same crystal form reveals that this mutation destabilizes the folding of the C-terminal region. These structures prove that subtle modifications to Prx structures can substantially influence enzymatic properties. We also present a simple thermodynamic framework for understanding the various mixtures of FF and LU conformations seen in these structures. On the basis of this framework, we rationalize how physiologically relevant regulatory post-translational modifications may modulate activity, and we propose a nonconventional strategy for designing selective Prx inhibitors.
PDB ID: 4MABDownload
MMDB ID: 115313
PDB Deposition Date: 2013/8/15
Updated in MMDB: 2013/11
Experimental Method:
x-ray diffraction
Resolution: 1.9  Å
Source Organism:
Similar Structures:
Biological Unit for 4MAB: decameric; determined by author and by software (PISA)
Molecular Components in 4MAB
Label Count Molecule
Proteins (10 molecules)
Alkyl Hydroperoxide Reductase Subunit C(Gene symbol: ahpC)
Molecule annotation
Chemicals (15 molecules)
* Click molecule labels to explore molecular sequence information.

Citing MMDB