A novel peroxiredoxin of the plant Sedum lineare is a homologue of Escherichia coli bacterioferritin co-migratory protein (Bcp)

We cloned a gene encoding a 17-kDa protein from a cDNA library of the plant Sedum lineare and found that its deduced amino acid sequence showed simila rities to those of Escherichia coil bacterioferritin co-migratory protein ( Bcp) and its homologues, which comprise a discrete group associated with th e peroxiredoxin (Prx) family. Studies of the recombinant 17-kDa protein pro duced in E. coli cells revealed that it actually had a thioredoxin-dependen t peroxidase activity, the hallmark of the Prx family. PrxQ, as we now desi gnate the 17-kDa protein, had two cysteine residues (Cys-44 and Cys-49) wel l conserved among proteins of the Bcp group. These two cysteines were demon strated to be essential for the thioredoxin-dependent peroxidase activity b y analysis of mutant proteins, suggesting that these residues are involved in the formation of an intramolecular disulphide bond as an intermediate in the reaction cycle. Expression of PrxQ suppressed the hypersensitivity of an E. coli bcp mutant to peroxides, indicating that it might exert an antio xidant activity in vivo.