FIG. 5.
Components of the maturation process for N2O reductase and topology. Single uppercase letters indicate the products of nos genes. The numbers indicate the approximate protein masses (in kilodaltons). Cu-containing proteins are indicated. NosZ is shown as a dimer, but otherwise no inferences about stoichiometries of protein complexes are drawn, nor is the composition of the Tat translocon indicated other than to show the supportive role of TatE. NosF has ATPase activity (Honisch and Zumft, unpublished data). NosD belongs to a protein family with carbohydrate and sugar hydrolase signatures (10). [S] is a sulfur donor whose chemical nature is not known. NosL is shown with a lipid anchor. Cu may enter the periplasm via NosA or another porin. The membrane-bound NosR carries putative FeS groups in its cytoplasmic domain and may have other functions in addition to acting as a transcriptional regulator for nosZ. IM and OM, cytoplasmic and outer membranes, respectively. For further discussion see the text.