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. 2010 May 26;132(20):6894-5.
doi: 10.1021/ja101737f.

Conformational gating of electron transfer from the nitrogenase Fe protein to MoFe protein

Karamatullah Danyal  1 , Diana Mayweather, Dennis R Dean, Lance C Seefeldt, Brian M Hoffman
Affiliations

Conformational gating of electron transfer from the nitrogenase Fe protein to MoFe protein

Karamatullah Danyal et al. J Am Chem Soc. .

Abstract

The nitrogenase Fe protein contains a [4Fe-4S] cluster and delivers one electron at a time to the catalytic MoFe protein. During this electron delivery, the Fe protein in its [4Fe-4S](1+) reduced state (Fe(red)) binds two MgATP and forms a complex with the MoFe protein, with subsequent transfer of one electron to the MoFe protein in a reaction coupled to the hydrolysis of two ATP. Crystal structures with the nitrogenase complex in different nucleotide-bound states show major conformational changes which provide a structural underpinning to suggestions that intercomponent electron transfer (ET) is "gated" by conformational changes of the complex and/or of its component proteins. Although electron delivery is coupled to ATP hydrolysis, their connection is puzzling, for it appears that ET precedes both ATP hydrolysis and Pi release. We here test the gating hypothesis with studies of the intracomplex oxidation of Fe(red) by MoFe protein in the presence of a variety of solutes. Conformational control of this process (gating) is revealed by the finding that it responds to changes in osmotic pressure (but not viscosity), with no fewer than 80 waters being bound during the reaction. The absence of a solvent kinetic isotope effect further implies that ATP hydrolysis does not occur during the rate-limiting step of ET.

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Figures

Figure 1
Figure 1
Representation of complexes between Fe protein (top) and MoFe protein (bottom) in ATP- like (dashed) and ADP-like bound forms; (adapted from Tezcan and coworkers3).
Figure 2
Figure 2
Stopped-flow oxidation of Fered within [Fered(MgATP)2: MoFe] complex. Sucrose concentrations vary from 0 to 2 m. Traces for m = 0 in H2O and D2O overlay so that the latter would barely be visible if shown, and hence is not (traces have same k2 within error). Conditions: 75 μM Fe protein, 20 μM MoFe protein; 100 mM HEPES buffer, pH 7.4: 25 C.
Figure 3
Figure 3
Log of the rate constants for oxidation of Fered within the [Fered(MgATP)2: MoFe] complex as a function of osmolyte concentration.
See this image and copyright information in PMC

References

    1. Burgess BK, Lowe DJ. Chemical Reviews (Washington, D C) 1996;96:2983–3011. - PubMed
    1. Seefeldt LC, Hoffman BM, Dean DR. Annu Rev Biochem. 2009;78:701–722. - PMC - PubMed
    1. Tezcan FA, Kaiser JT, Mustafi D, Walton MY, Howard JB, Rees DC. Science (Washington, DC, U S) 2005;309:1377–1380. - PubMed
    1. Rees DC, Tezcan FA, Haynes CA, Walton MY, Andrade S, Einsle O, Howard JB. Phil Trans R Soc A. 2005;363:971–984. - PubMed
    1. Lanzilotta WN, Parker VD, Seefeldt LC. Biochemistry. 1998;37:399–407. - PubMed

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