Figure 1.

Nitrogenase cofactor, synthetic compound and protein scaffold. Structural models of the M-cluster (A) and the Fe₆^RHH compound (B), and the overlay of the two structures (C) in top (left) and side (right) views. PDB entry 3U7Q^[12] and data from ref. 15 were used to generate these models. Atoms are colored as follows: Fe, orange; S, yellow; Mo, cyan; O, red; C (M-cluster), light gray; C (Fe₆^RHH), green; H (Fe₆^RHH), gray. (D) Comparison of the α-subunits of the wild-type NifDK (NifDK^holo) and the cofactor-deficient NifDK (NifDK^apo), which reveals the presence of a positively-charged cofactor-insertion path in NifDK^apo (right) that is closed up in NifDK^holo upon insertion of the cofactor (left).