Model of the Fe protein cycle with reduction preceding nucleotide exchange.
1, the MgATP-bound Fe protein (tan, PDB code 4WZB) transiently associates with one-half of the MoFe protein (orange, PDB code 2NIP). 2, the MgATP-bound Fe protein transfers an electron to the MoFe protein upon complex formation. 3, nucleotide hydrolysis of 2MgATP to 2MgADP and 2Pi occurs. 4, inorganic phosphate is released from the Fe protein (MgADP2)–MoFe protein complex. 5, the MoFe protein and MgADP-bound Fe protein dissociate. 6, Fld (violet, PDB code 1YOB) delivers an electron to the MgADP-bound Fe protein (light blue, PDB code 1FP6). 7, MgADP is exchanged for MgATP, and this induces structural changes in the MgATP-bound Fe protein to promote interactions with the MoFe protein.