On the basis of elastic light scattering, we have compared the capacity of the multi-block,
surfactant copolymers Poloxamer 108 (P108), Poloxamer 188 (P188), and Tetronic 1107
(T1107), of average molecular weight 4700, 8400, and 15,000, respectively, with that
of polyethylene glycol (PEG, molecular weight 8000) to suppress aggregation of heat-denatured
hen egg white lysozyme (HEWL) and bovine serum albumin (BSA). We also compared the
capacity of P188 to that of PEG to suppress aggregation of carboxypeptidase A denatured
in the presence of trifluoroethanol and to facilitate recovery of catalytic activity.
In contrast to the multi-block copolymers, PEG had no effect in inhibiting aggregation
of HEWL or of carboxypeptidase A with the recovery of catalytic activity. At very
high polymer:protein ratios (>or=10:1), PEG increased aggregation of heat-denatured
HEWL and BSA, consistent with its known properties to promote macromolecular crowding
and crystallization of proteins. At a polymer:protein ratio of 2:1, the tetra-block
copolymer T1107 was the most effective of the three surfactant copolymers, completely
suppressing aggregation of heat-denatured HEWL. At a T1107:BSA ratio of 10:1, the
poloxamer suppressed aggregation of heat-denatured BSA by 50% compared to that observed
in the absence of the polymer. We showed that the extent of suppression of aggregation
of heat-denatured proteins by multi-block surfactant copolymers is dependent on the
size of the protein and the copolymer:protein molar ratio. We also concluded that
at least one of the tertiary nitrogens in the ethylene-1,2-diamine structural core
of the T1107 copolymer is protonated, and that this electrostatic factor underlies
its capacity to suppress aggregation of denatured proteins more effectively than nonionic,
multi-block poloxamers. These results indicate that amphiphilic, surfactant, multi-block
copolymers are efficient as additives to suppress aggregation and to facilitate refolding
of denatured proteins in solution. Because of these properties, multi-block, surfactant
copolymers are suitable for application to a variety of biotechnological and biomedical
problems in which refolding of denatured or misfolded proteins and suppression of
aggregation are important objectives.