1-Cys peroxiredoxin, a bifunctional enzyme with glutathione peroxidase and phospholipase A2 activities

This report provides definitive evidence that the protein 1-Cys peroxiredoxin is a bifunctional ("moonlighting") enzyme with two distinct active sites. We have previously shown that human, rat, and bovine lungs contain an acidic Ca2+-independent phospholipase A(2) (aiPLA(2)). The cDNA encoding aiPLA(2) was found to be identical to that of a non-selenium glutathione peroxidase (NSGPx). Protein expressed using a previously reported E, coli construct which has a His-tag and 50 additional amino acids at the NH2 terminus, did not exhibit aiPLA(2) activity. A new construct which contains the His-tag plus two extra amino acids at the COOH terminus when expressed in Escherichia coli generated a protein that hydrolyzed the sn-2 acyl chain of phospholipids at pH 4, and exhibited NSGPx activity with H2O2 at pH 8. The expressed 1-Cys peroxiredoxin has identical functional properties to the native lung enzyme: aiPLA(2) activity is inhibited by the serine protease inhibitor, diethyl p-nitrophenyl phosphate, by the tetrahedral mimic 1-hexadecyl-3-trifluoroethylglycero-sn-2-phosphomethanol (MJ33), and by 1-Cys peroxiredoxin monoclonal antibody (mAb) 8H11 but these agents have no effect on NSGPx activity; NSGPx activity is inhibited by mercaptosuccinate and by 1-Cys peroxiredoxin mAb 8B3 antibody which have no effect on aiPLA(2) activity. Mutation of Ser(32) to Ala abolishes aiPLA(2) activity, yet the NSGPx activity remains unaffected; a Cys(47) to Ser mutant is devoid of peroxidase activity but aiPLA(2) activity remains intact. These results suggest that Ser32 in the GDSWG consensus sequence provides the catalytic nucleophile for the hydrolase activity of aiPLA(2) while Cys47 in the PVCTTE consensus sequence is at the active site for peroxidase activity. The bifunctional catalytic properties of 1-Cys peroxiredoxin are compatible with a simultaneous role for the protein in the regulation of phospholipid turnover as well as in protection against oxidative injury.