1FP4

CRYSTAL STRUCTURE OF THE ALPHA-H195Q MUTANT OF NITROGENASE

Summary for 1FP4

• Entry DOI: 10.2210/pdb1fp4/pdb
• Related: 1MIO 2MIN
• Descriptor: NITROGENASE MOLYBDENUM-IRON PROTEIN ALPHA CHAIN, NITROGENASE MOLYBDENUM-IRON PROTEIN BETA CHAIN, 3-HYDROXY-3-CARBOXY-ADIPIC ACID, ... (7 entities in total)
• Functional Keywords: iron-sulfur-molybdenum protein, oxidoreductase
• Biological source: Azotobacter vinelandii; More
• Total number of polymer chains: 4
• Total formula weight: 233227.71

Authors

Sorlie, M.,Christiansen, J.,Lemon, B.J.,Peters, J.W.,Dean, D.R.,Hales, B.J. (deposition date: 2000-08-30, release date: 2002-11-20, Last modification date: 2024-05-29)

Primary citation

Sorlie, M.,Christiansen, J.,Lemon, B.J.,Peters, J.W.,Dean, D.R.,Hales, B.J.
Mechanistic features and structure of the nitrogenase alpha-Gln195 MoFe protein
Biochemistry, 40:1540-1549, 2001

PubMed Abstract: EPR signals observed under CO and C(2)H(2) during nitrogenase turnover were investigated for the alpha-Gln(195) MoFe protein, an altered form for which the alpha-His(195) residue has been substituted by glutamine. Under CO, samples show S = 1/2 hi- and lo-CO EPR signals identical to those recognized for the wild-type protein, whereas the S = 3/2 signals generated under high CO/high flux conditions differ. Previous work has revealed that the EPR spectrum generated under C(2)H(2) exhibits a signal (S(EPR1)) originating from the FeMo-cofactor having two or more bound C(2)H(2) adducts and a second signal (S(EPR2)) arising from a radical species [Sørlie, M., Christiansen, J., Dean, D. R., and Hales, B. J. (1999) J. Am. Chem. Soc. 121, 9457-9458]. Pressure-dependent studies show that the intensity of these signals has a sigmoidal dependency at low pressures and maximized at 0.1 atm C(2)H(2) with a subsequent decrease in steady-state intensity at higher pressures. Analogous signals are not recognized for the wild-type MoFe protein. Analysis of the principal g-factors of S(EPR2) suggests that it either represents an unusual metal cluster or is a carboxylate centered radical possibly originating from homocitrate. Both S(EPR1) and S(EPR2) exhibit similar relaxation properties that are atypical for S = 1/2 signals originating from Fe-S clusters or radicals and indicate a coupled relaxation pathway. The alpha-Gln(195) MoFe protein also exhibits these signals when incubated under turnover conditions in the presence of C(2)H(4). Under these conditions, additional inflections in the g 4-6 region assigned to ground-state transitions of an S = 3/2 spin system are also recognized and assigned to turnover states of the MoFe protein without C(2)H(4) bound. The structure of alpha-Gln(195) was crystallographically determined and found to be virtually identical to that of the wild-type MoFe protein except for replacement of an NuH-S hydrogen bond interaction between FeMo-cofactor and the imidazole side chain of alpha-His(195) by an analogous interaction involving Gln.

PubMed: 11327812
DOI: 10.1021/bi0013997

Experimental method

X-RAY DIFFRACTION (2.5 Å)