Expression, purification, and characterization of NosL, a novel Cu(II) protein of the nitrous oxide reductase (nos) gene cluster

NosL, one of the accessory proteins of the nos (nitrous oxide reductase) ge ne cluster, has been heterologously expressed, purified, and characterized. NosL is a monomeric protein of 18,540 MW that specifically and stoichiomet rically binds Cu(I). The copper ion in NosL is ligated by a Cys residue, an d one Met and one His are thought to serve as the other ligands. While it i s possible to oxidize Cu(I)-NosL with ferricyanide; the Cu(II) ion thus for med appears to dissociate from the protein. The function of Cu(I)NosL is no t yet known, but the data indicate that NosL does not act as an electron tr ansfer partner to nitrous oxide reductase. NosL is encoded on the same tran script as three other gene products (NosD, NosF, and NosY). These have been shown to be required for assembly of the active site in nitrous oxide redu ctase, which is thought to be a copper cluster. Accordingly, it is possible that NosL is a copper chaperone involved in metallocenter assembly.