Mapping the site(s) of MgATP and MgADP interaction with the nitrogenase of Azotobacter vinelandii. Lysine 15 of the iron protein plays a major role in MgATP interaction.

The Critical E4 State of Nitrogenase Catalysis

“…This was interpreted to indicate that substrate binding occurs on the cluster face situated below this residue, in particular at Fe6, with a possible end-on binding of N 2 to this site . As a result, the Fe6–C bond should elongate, resulting in a trigonal bipyramidal geometry that inspired extensive synthetic work by Peters and co-workers, who showed that such complexes would not only bind but also activate and catalytically reduce N 2 . − Similarly, Seefeldt, Hoffman, and Dean suggested that the formation of hydrides would occur on the same cluster face in the form of bridging hydrides that are typically less likely to be lost through protonation than their terminal counterparts. , The precise placement of such hydrides remained an open question, as much as the more fundamental point as to which exact features of the cluster determine this reactivity.…”

“…47−49 Similarly, Seefeldt, Hoffman, and Dean suggested that the formation of hydrides would occur on the same cluster face in the form of bridging hydrides that are typically less likely to be lost through protonation than their terminal counterparts. 50,51 The precise placement of such hydrides remained an open question, as much as the more fundamental point as to which exact features of the cluster determine this reactivity.…”

Role of Nucleotides in Nitrogenase Catalysis

“…Evidence supporting this model was provided by characterization of altered Fe proteins substituted at either the Lys-15 37,40 or Asp-125 41 able to bind MgATP, but this binding event is not communicated to the [4Fe-4S] cluster. 37 Conversely, substitution by Glu at the Asp-125 position results in an Fe protein that mimics certain properties of the MgATPbound form when it has MgADP, rather than MgATP, bound.…”

“…Evidence supporting this model was provided by characterization of altered Fe proteins substituted at either the Lys-15 37,40 or Asp-125 41 able to bind MgATP, but this binding event is not communicated to the [4Fe-4S] cluster. 37 Conversely, substitution by Glu at the Asp-125 position results in an Fe protein that mimics certain properties of the MgATPbound form when it has MgADP, rather than MgATP, bound. 41 This latter result makes sense when it is considered that the extra methylene group in Glu should permit it to reach the R-and β-phosphates of bound MgADP in a way that might approximate the normal Asp interaction with the β-and γ-phosphates of MgATP (Figure 3).…”

Roles for Nucleotides in Nitrogenase Catalysis

“…It is known that nucleotide binding to the Fe protein results in protein conformational changes that impact the properties of the [4Fe-4S] cluster (Burgess, Lowe, 1996). From a series of site-directed mutagenesis studies (Lanzilotta et al, 1997;Seefeldt et al, 1992;Seefeldt, Mortenson, 1993;Wolle et al, 1992) and x-ray crystal structures of both the uncomplexed Fe protein (Georgiadis et al, 1992;Schlessman et al, 1998) and the Fe protein complexed to the MoFe protein (Rees et al, 1998;Schindelin et al, 1997), it is clear that nucleotides bind some 20 Å away from the [4Fe-4S] cluster (Georgiadis et al, 1992) and the MoFe protein docking surface (Schindelin et al, 1997). Thus, this demands that nucleotides act via long range protein conformational changes.…”