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J. Biol. Chem., Vol. 263, Issue 6, 2794-2801, Feb, 1988
TG Consler, EC Uberbacher, GJ Bunick, MN Liebman and JC Lee
The effects of ligands on the structure of rabbit muscle pyruvate kinase
were studied by small angle neutron scattering. The radius of gyration, RG,
decreases by about 1 A in the presence of the substrate
phosphoenolpyruvate, but increases by about the same magnitude in the
presence of the allosteric inhibitor phenylalanine. With increasing pH or
in the absence of Mg2+ and K+, the RG of pyruvate kinase increases. Hence,
there is a 2-A difference in RG between two alternative conformations.
Length distribution analysis indicates that, under all experimental
conditions which increase the radius of gyration, there is a pronounced
increase observed in the probability for interatomic distance between 80
and 110 A. These small angle neutron scattering results indicate a
"contraction" and "expansion" of the enzyme when it transforms between its
active and inactive forms. Using the alpha- carbon coordinates of
crystalline cat muscle pyruvate kinase, a length distribution profile was
calculated, and it matches the scattering profile of the inactive form.
These observations are expected since the crystals were grown in the
absence of divalent cations (Stuart, D. I., Levine, M., Muirhead, H., and
Stammers, D. K. (1979) J. Mol. Biol. 134, 109-142). Hence, results from
neutron scattering, x-ray crystallographic, and sedimentation studies
(Oberfelder, R. W., Lee, L. L.-Y., and Lee, J.C. (1984) Biochemistry 23,
3813-3821) are totally consistent with each other. With the aid of computer
modeling, the crystal structure has been manipulated in order to effect
changes that are consistent with the conformational change described by the
solution scattering data. The structural manipulation involves the rotation
of the B domain relative to the A domain, leading to the closure of the
cleft between these domains. These manipulations resulted in the generation
of new sets of atomic (C-alpha) coordinates, which were utilized in
calculations, the result of which compared favorably with the solution
data.
Domain interaction in rabbit muscle pyruvate kinase. II. Small angle neutron scattering and computer simulation
E. A. Doisy Department of Biochemistry, St. Louis University School of Medicine, Missouri 63104.
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