Quantitative assessment of the relative contributions of steric repulsion and chemical interactions to macromolecular crowding - PubMed (original) (raw)

Quantitative assessment of the relative contributions of steric repulsion and chemical interactions to macromolecular crowding

Allen P Minton. Biopolymers. 2013 Apr.

Abstract

The term "macromolecular crowding" denotes the combined effects of high volume fractions of nominally unrelated macromolecules upon the equilibrium and transport properties of all macrosolutes, dilute as well as concentrated, in the crowded medium. We present a formal partitioning of the total crowding effect into contributions from steric exclusion (excluded volume) and weak, nonspecific attractive interactions between a concentrated "crowding agent" and reactant and product species present at trace concentration. A numerical example of the combined effect of both steric and chemical interactions between crowder and tracer upon the reversible dimerization of tracer is presented, based upon reasonable estimates of the magnitude of both repulsive and attractive interactions between tracer and crowder species.

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Figures

Figure 1

Figure 1

Thermodynamic cycle indicating free energy changes accompanying dimerization in dilute and crowded media, and transfer of monomer and dimer from a dilute to a crowded medium.

Figure 2

Figure 2

Equivalent convex particles described in text superimposed on molecular models of monomeric and dimeric alpha-chymotrypsin (PDB 4CHA).

Figure 3

Figure 3

Temperature dependence of the equilibrium association constant for binding of urea to unfolded ribonuclease A, calculated as described in text.

Figure 4

Figure 4

Dependence of the crowding factor for dimerization of trace molecules upon volume fraction of background species B and temperature, calculated as described in text. Dashed curve: calculated for pure excluded volume – no chemical interaction. Solid curves: red, green, blue, magenta, and black curves are calculated for T = 40, 30, 20, 10, and 0°C respectively.

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