Proteins aggregation-disaggregation

Heating milk to > 100°C for 15 to 20 min, as in the forewarming of milk for evaporated milk manufacture, effectively denatures and complexes whey proteins with casein micelles and causes simultaneous aggregation and disaggregation of these complexed milk protein aggregates (Morr 1975). 

Cashikar AG, Duennwald M, Lindquist SL (2005) A chaperone pathway in protein disaggregation. Hsp26 alters the nature of protein aggregates to facilitate reactivation by Hspl04. J Biol Chem 280 23869-23875... 

Diamant, S., Ben-Zvi, A. P., Bukau, B., and Goloubinoff, P. (2000). Size-dependent disaggregation of stable protein aggregates by the DnaK chaperone machinery. J. Biol. Chem. 275, 21107-21113. 

Proteins of egg white denature more rapidly than those of whey protein concentrate (13, 34). However, isolated p-lactoglobulin from the whey concentrate was more susceptible to surface denaturation than egg white ovalbumin. These data suggest that whey contains substances that protect the proteins from surface denaturation and may account for the lower stability of whey protein concentrate foams than those of egg white protein. A balance between the disaggregation effect of select pH values and the tendency toward greater aggregation of proteins at higher heating temperatures were correlated closely with maximum foam stability (13, 15). 

Figure 4. ORD of mitochondrial structural protein in the disaggregated state at pH 11 and the aggregated state at pH 9. Spectra were taken in distilled water, and pH was adjusted with HCl or KOH...

Under certain conditions, the stress-70 proteins can participate in the renaturation of denatured or inactivated proteins. The renaturation capabilities of E. coli dnaK protein have been most extensively documented. It has been shown that in vitro, dnaK can protect E. coli RNA polymerase from aggregation when the polymerase is incubated at elevated temperatures that would normally result in loss of activity, and, further, that dnaK can disaggregate and reactivate polymerase, once it has been inactivated by heat denaturation (Skowyra et al., 1990). These activities are absolutely dependent on ATP hydrolysis. The mutant dnaK756 protein is effective in protecting active RNA polymerase against heat inactivation, but is incapable of disaggregating and reactivating polymerase, once it has been heat inactivated. 

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