1fp4
From Proteopedia
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CRYSTAL STRUCTURE OF THE ALPHA-H195Q MUTANT OF NITROGENASE
Overview
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 [Sorlie, 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.
About this Structure
1FP4 is a Protein complex structure of sequences from Azotobacter vinelandii with CA, HCA, CFM and CLP as ligands. Active as Nitrogenase, with EC number 1.18.6.1 Full crystallographic information is available from OCA.
Reference
Mechanistic features and structure of the nitrogenase alpha-Gln195 MoFe protein., Sorlie M, Christiansen J, Lemon BJ, Peters JW, Dean DR, Hales BJ, Biochemistry. 2001 Feb 13;40(6):1540-9. PMID:11327812
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