Structure-based Insights into the Catalytic Power and Conformational Dexterity of Peroxiredoxins

Abstract

Peroxiredoxins (Prxs), some of nature's dominant peroxidases, use a conserved Cys residue to reduce peroxides. They are highly expressed in organisms from all kingdoms, and in eukaryotes they participate in hydrogen peroxide signaling. Seventy-two Prx structures have been determined that cover much of the diversity of the family. We review here the current knowledge and show that Prxs can be effectively classified by a structural/evolutionary organization into six subfamilies followed by specification of a 1-Cys or 2-Cys mechanism, and for 2-Cys Prxs, the structural location of the resolving Cys. We visualize the varied catalytic structural transitions and highlight how they differ depending on the location of the resolving Cys. We also review new insights into the question of how Prxs are such effective catalysts: the enzyme activates not only the conserved Cys thiolate but also the peroxide substrate. Moreover, the hydrogen-bonding network created by the four residues conserved in all Prx active sites stabilizes the transition state of the peroxidatic S(N)2 displacement reaction. Strict conservation of the peroxidatic active site along with the variation in structural transitions provides a fascinating picture of how the diverse Prxs function to break down peroxide substrates rapidly.

Multilevel Regulation of 2-Cys Peroxiredoxin Reaction Cycle by S-Nitrosylation

“…Structural studies suggest that disulfide bond formation between C P and C R is accompanied by stabilization of a locally unfolded conformation of the active site, which leads to destabilization of the decamer (for review, see Ref. 34). Nitrosylation-mediated disulfide formation between C P and C R may similarly destabilize the decamer.…”

“…2D). Thus, it appears that nitrosylation of Cys-52 promotes disulfide bond formation with Cys-173, thereby disrupting the decameric structure (34).…”

A Redox 2-Cys Mechanism Regulates the Catalytic Activity of Divergent Cyclophilins

“…Interestingly, the process involved in such disulfide bridge formation in CsCyp seems to be a conserved redox 2-Cys mechanism observed in the catalytic cycle of peroxiredoxins (Hall et al, 2011). In this group of enzymes, a Cys referred to as peroxidatic Cys is located at the end of a helix (as Cys-40 is in divergent Cyps).…”

“…In this group of enzymes, a Cys referred to as peroxidatic Cys is located at the end of a helix (as Cys-40 is in divergent Cyps). When this Cys is in the reduced state, the helix adopts a fully folded (FF) conformation, whereas under oxidizing conditions (S-S bond), it adopts a locally unfolded (LU) conformation, which is required for disulfide bond formation between the peroxidatic Cys and the so-called resolving Cys located at the C terminus of the protein, just as Cys-168 is in CsCyp (Hall et al, 2011). Thus, analogously to peroxiredoxins, an FF→LU transition in CsCyp, mediated or stabilized by the disulfide bond formation between Cys-40 and Cys-168, would cause a significant change in the conformation of the divergent loop, as envisaged by our mechanistic model (Fig.…”

Model for the Exceptional Reactivity of Peroxiredoxins 2 and 3 with Hydrogen Peroxide

“…There are six subfamilies (Prx1, Prx6, AhpE (one-cysteine peroxiredoxin from Mycobacterium tuberculosis), Prx5, Tpx, and bacterioferritin comigratory protein), categorized by amino acid sequence, which share a similar catalytic cycle. A number of highly conserved amino acid residues promote similar structures around their active site cysteine (peroxidatic cysteine; C p ) (9). Based on mechanistic considerations they are further subcategorized into 1-Cys and 2-Cys Prx.…”