 |
PDBsum entry 1fp4
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
 |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
Oxidoreductase
|
PDB id
|
|
|
|
1fp4
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
 |
Contents |
 |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
* Residue conservation analysis
|
|
|
|
|
References listed in PDB file
|
|
|
Key reference
|
|
|
Title
|
|
Mechanistic features and structure of the nitrogenase alpha-Gln195 mofe protein.
|
|
|
Authors
|
|
M.Sørlie,
J.Christiansen,
B.J.Lemon,
J.W.Peters,
D.R.Dean,
B.J.Hales.
|
|
|
Ref.
|
|
Biochemistry, 2001,
40,
1540-1549.
[DOI no: ]
|
|
|
PubMed id
|
|
|
|
|
|
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.
|
|
|
|
|
|
|
