A Modified Lumry-Eyring Analysis for the Determination of the Predominant Mechanism Underlying the Diminution of Protein Aggregation by Glycerol

Aggregation of aspartate-β-semialdehyde dehydrogenase (ASD) was analyzed by applying modified Lumry-Eyring with nucleated polymerization (LENP) model. Intrinsic nucleation time scales were determined. In absence of glycerol, ASD undergoes concentration and time-dependent polymerization into low-molecular weight soluble aggregates and thereafter condensation into insoluble aggregates. In the presence of increasing solvent glycerol concentration, the aggregation becomes more and more nucleation dominated, with slower polymerization to low-molecular weights soluble aggregates, without any condensation into insoluble aggregates. Effective nucleus size as well as the number of monomers in each irreversible growth event were sensitive to the changes in solvent glycerol concentration. Glycerol-directed diminution of aggregation appears to be largely due to the inhibition of rearrangement (decreased nucleation rearrangement rate coefficient, K _r,x) because of compaction induced due to preferential hydration, thus, preventing the soluble aggregates from locking into irreversible soluble nuclei. Appreciably decreased K _r,x (as compared to nucleation dissociation constant, K _d,x), appears to be responsible for increased nucleus size at higher solvent glycerol concentration. This study explains how modified LENP model can be applied to determine the predominant mechanism responsible for the diminution of aggregation by polyhydric alcohols (glycerol).