J. Biol. Chem., Vol. 265, Issue 13, 7351-7359, 05, 1990
Kinetic analysis of the pre-equilibrium steps in the self-assembly of RecA protein from Escherichia coli
DH Wilson and AS Benight
Department of Chemistry, University of Illinois, Chicago 60680.
Total intensity light scattering is employed to investigate the self-
assembly kinetics of RecA protein. Reaction conditions are employed where
the kinetics of self-assembly are slow enough to yield reliable scattered
intensity measurements over the range of scattering angles from 40 to 130
degrees as a function of time. From these measurements the time-dependent
behavior of the weight average molecular weight, Mr, and radius of
gyration, RG, of the associating protein species as a function of [MgCl2],
[NaCl], [RecA], and pH was determined. The temperature dependence of RecA
self-assembly was also investigated and allowed an evaluation of the
activation thermodynamic parameters of association. Results reveal RecA
self-assembly is bi-phasic under all conditions examined. The first phase,
referred to as "filamentation" is second-order in [RecA] and occurs via a
quasi linear condensation scheme with an Arrhenius activation energy of
88.6 kcal/mol. Filamentation assembly involves the uptake of one proton,
one MgCl2, the release of five to six NaCls, and is driven by the release
of approximately 70 water molecules. The evaluated activation parameters of
the first kinetic phase are consistent with the proposition that linear
self-assembly of RecA protein into ordered filaments is entropically
driven. The second kinetic phase, referred to as "bundling" is greater than
second-order in both [RecA] and [MgCl2], is considerably slower that
filamentation assembly, and is apparently initiated by 2nd order collisions
of linear filaments.