3EMP

Crystal Structure of the S-acetanilide modified form of C165S AhpC

Summary for 3EMP

• Entry DOI: 10.2210/pdb3emp/pdb
• Related: 1N8J 1YF1
• Descriptor: Alkyl hydroperoxide reductase subunit C (1 entity in total)
• Functional Keywords: oxidoreductase, ahpc, peroxiredoxin, antioxidant, peroxidase, redox-active center
• Biological source: Salmonella typhimurium
• Cellular location: Cytoplasm : P0A251
• Total number of polymer chains: 5
• Total formula weight: 103125.61

Authors

Karplus, P.A.,Hall, A. (deposition date: 2008-09-24, release date: 2009-03-03, Last modification date: 2023-09-06)

Primary citation

Nelson, K.J.,Parsonage, D.,Hall, A.,Karplus, P.A.,Poole, L.B.
Cysteine pK(a) Values for the Bacterial Peroxiredoxin AhpC
Biochemistry, 47:12860-12868, 2008

PubMed Abstract: Salmonella typhimurium AhpC is a founding member of the peroxiredoxin family, a ubiquitous group of cysteine-based peroxidases with high reactivity toward hydrogen peroxide, organic hydroperoxides, and peroxynitrite. For all of the peroxiredoxins, the catalytic cysteine, referred to as the peroxidatic cysteine (C(P)), acts as a nucleophile in attacking the peroxide substrate, forming a cysteine sulfenic acid at the active site. Because thiolates are far stronger nucleophiles than thiol groups, it is generally accepted that cysteine-based peroxidases should exhibit pK(a) values lower than an unperturbed value of 8.3-8.5. In this investigation, several independent approaches were used to assess the pK(a) of the two cysteinyl residues of AhpC. Methods using two different iodoacetamide derivatives yielded unperturbed pK(a) values (7.9-8.7) for both cysteines, apparently due to reactivity with the wrong conformation of C(P) (i.e., locally unfolded and flipped out of the active site), as supported by X-ray crystallographic analyses. A functional pK(a) of 5.94 +/- 0.10 presumably reflecting the titration of C(P) within the fully folded active site was obtained by measuring AhpC competition with horseradish peroxidase for hydrogen peroxide; this value is quite similar to that obtained by analyzing the pH dependence of the epsilon(240) of wild-type AhpC (5.84 +/- 0.02) and similar to those obtained for two typical 2-cysteine peroxiredoxins from Saccharomyces cerevisiae (5.4 and 6.0). Thus, the pK(a) value of AhpC balances the need for a deprotonated thiol (at pH 7, approximately 90% of the C(P) would be deprotonated) with the fact that thiolates with higher pK(a) values are stronger nucleophiles.

PubMed: 18986167
DOI: 10.1021/bi801718d

Experimental method

X-RAY DIFFRACTION (4 Å)