d(1) haem biogenesis - assessing the roles of three nir gene products.
The synthesis of the modified tetrapyrrole known as d(1) 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 cd(1) 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 cd(1) that binds d(1), was validated by recombinant production and characterization of NirN. A NirN-d(1) haem complex was demonstrated to release the cofactor to a semi-apo form of cytochrome cd(1) from which d(1) was extracted, suggesting a role for NirN in the assembly of cytochrome cd(1) (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-d(1) complex.
Department of Biochemistry, University of Oxford, UK.
Richard S
RS
Zajicek
Shilpa
S
Bali
Simon
S
Arnold
Amanda A
AA
Brindley
Martin J
MJ
Warren
Stuart J
SJ
Ferguson
D027321:Anion Transport Proteins / Q000502:physiology; D001419:Bacteria / Q000378:metabolism*; D003580:Cytochromes / Q000502:physiology; D029968:Escherichia coli Proteins / Q000502:physiology; D006418:Heme / Q000031:analogs & derivatives / Q000096:biosynthesis*; D009572:Nitrite Reductases / Q000502:physiology*; D042084:Paracoccus pantotrophus / Q000235:genetics / Q000254:growth & development; D014577:Uroporphyrinogens / Q000378:metabolism; D014578:Uroporphyrins / Q000096:biosynthesis
D027321:Anion Transport Proteins; D003580:Cytochromes; D029968:Escherichia coli Proteins; C490243:NirC protein, E coli; D014577:Uroporphyrinogens; D014578:Uroporphyrins; D006418:Heme; C063209:15,23-dihydrosirohydrochlorin; D009572:Nitrite Reductases; C028123:nitrite reductase (NO-forming)