tailieunhanh - Báo cáo khoa học: d1 haem biogenesis – assessing the roles of three nir gene products

The synthesis of the modified tetrapyrrole known asd1haem requires sev-eral dedicated proteins which are coded for by a set of genes that are often found adjacent to the structural gene, nirS, for cytochrome cd1 nitrite reductase. NirE, the product of the first gene in the nirbiogenesis operon, was anticipated to catalyse the conversion of uroporphyrinogen III into precorrin-2 | ỊFEBS Journal d1 haem biogenesis - assessing the roles of three nir gene products Richard S. Zajicek1 z Shilpa Bali1 z Simon Arnold1 Amanda A. Brindley2 Martin J. Warren2 and Stuart J. Ferguson1 1 Department of Biochemistry University of Oxford UK 2 Department of Biosciences University of Kent Canterbury UK Keywords d1 haem nitrite reductase precorrin-2 sirohydrochlorin uroporphyrinogen III Correspondence S. J. Ferguson Department of Biochemistry University of Oxford South Parks Road Oxford OX1 3QU UK Fax 44 01865 275259 Tel 44 01865 275240 E-mail These authors contributed equally to this work Received 2 July 2009 revised 28 August 2009 accepted 4 September 2009 doi The synthesis of the modified tetrapyrrole known as d1 haem requires several dedicated proteins which are coded for by a set of genes that are often found adjacent to the structural gene nirS for cytochrome cd1 nitrite reductase. NirE the product of the first gene in the nir biogenesis operon was anticipated to catalyse the conversion of uroporphyrinogen III into precorrin-2 this was confirmed but it was shown that this enzyme is less sensitive to product inhibition than similar enzymes that function in other biosynthetic pathways. Sequence analysis suggesting that one of these proteins NirN is a c-type cytochrome and has similarity to the part of cytochrome cd1 that binds d1 was validated by recombinant production and characterization of NirN. A NirN-d1 haem complex was demonstrated to release the cofactor to a semi-apo form of cytochrome cd1 from which d1 was extracted suggesting a role for NirN in the assembly of cytochrome cd1 NirS . However inactivation of nirN surprisingly led to only a marginal attenuation of growth of Paracoccus pantotrophus under anaerobic denitrifying conditions. As predicted NirC is a c-type cytochrome it was shown in vitro to be an electron donor to the NirN-d1 complex. Introduction The reduction of nitrite to .