Oligomeric protein associations: transition from stochastic to deterministic equilibrium

Abstract

Transfer of electronic excitation energy (sensitized fluorescence) between donor and acceptor fluorophores separately attached to dimer or tetramer proteins is used to demonstrate the exchange of subunits among the undissociated particles. In dimers subjected to a pressure that produces half-dissociation, the exchange occurs at a rate that approaches the rate of dissociation. In the tetramers of glyceraldehydephosphate dehydrogenase and lactate dehydrogenase at 0 degrees C, the times for subunit exchange are nearly 2 orders of magnitude, and at room temperature 5-10 times longer than the time required to reach the dissociation equilibrium. By application of a novel method, pressure is shown to preferentially increase the rate of dissociation in dimers and decrease the rate of association in tetramers. From these observations, we conclude that the tetramers constitute a heterogeneous population, the members of which are dissociated by pressure according to individual molecular properties that can be retained over periods of time much longer than the time for equilibration of the dissociation. The dissociation of dimers exhibits the characteristics of the classical stochastic chemical equilibria, while those of the tetramers, like the more complex protein aggregates, must already be considered similar to the deterministic mechanical equilibria of macroscopic bodies.

Characterization of a Partially Folded Monomer of the DNA-binding Domain of Human Papillomavirus E2 Protein Obtained at High Pressure

“…process complies with the law of mass action in the concentration range analyzed and that there is no significant conformational heterogeneity as observed in multisubunit complexes (34), tetramers (35), and more recently in a dimeric protein (36).…”

Dissociation of F‐actin induced by hydrostatic pressure

“…It should be noted that, for the dimeric proteins so far studied under pressure (Verjovski-Almeida et al, 1986;Ruan and Weber, 1988;Erijman and Weber, 1991 ;Coelho-Sampaio et al, 1993), there was a displacement in the pressure profile with changes in protein concentration. Recently, Erijman and Weber (1991) pointed out that in the polymeric aggregates that do not show appreciable concentration effects upon pressure-induced dissociation, the polymer probably constitutes a heterogencous population, each member having its own characteristic dissociation pressure. It is interesting to note that the dissociation of F-actin under pressure (at protein concentrations below the critical concentration) results in the accumulation of basically two populations (Fig.…”

“…3A). The dissociation of F-actin under pressure seems to be an interesting case that illustratcs the deterministic behavior of large polymeric aggregates, first characterized by Erijman and Weber (1991), for the dissociation of a number of tetrameric proteins.…”

“…c i the degree of dissociation of the aggregate and C the molar concentration of protein expressed as aggregate. The effect of hydrostatic pressure (p) on the apparent dissociation constant [K(p)] of polymeric proteins can be described by the relation (Paladini and Weber, 1981 ;Erijman and Weber, 1991) K…”

“…3B between peaks I and 11. It has been shown that hydrostatic pressure increases the rate of dissociation and decreases the rate of association of polymeric proteins (Erijman and Weber, 1991), thus decreasing the time required to attain equilibrium after a perturbation such as thc dilution of the polymer. The shift towards the monomer observed in Fig.…”