Functional interactions between nitrite reductase and nitric oxide reductase from Paracoccus denitrificans

摘要

Denitrification is a microbial pathway that constitutes an important part of the nitrogen cycle on earth. Denitrifying organisms use nitrate as a terminal electron acceptor and reduce it stepwise to nitrogen gas, a process that produces the toxic nitric oxide (NO) molecule as an intermediate. In this work, we have investigated the possible functional interaction between the enzyme that produces NO; the cdsub1/sub nitrite reductase (cdsub1/subNiR) and the enzyme that reduces NO; the c-type nitric oxide reductase (cNOR), from the model soil bacterium P. denitrificans. Such an interaction was observed previously between purified components from P. aeruginosa and could help channeling the NO (directly from the site of formation to the side of reduction), in order to protect the cell from this toxic intermediate. We find that electron donation to cNOR is inhibited in the presence of cdsub1/subNiR, presumably because cdsub1/subNiR binds cNOR at the same location as the electron donor. We further find that the presence of cNOR influences the dimerization of cdsub1/subNiR. Overall, although we find no evidence for a high-affinity, constant interaction between the two enzymes, our data supports transient interactions between cdsub1/subNiR and cNOR that influence enzymatic properties of cNOR and oligomerization properties of cdsub1/subNiR. We speculate that this could be of particular importance in vivo during metabolic switches between aerobic and denitrifying conditions.