Stability and gelation behavior of bovine serum albumin pre-aggregates in the presence of calcium chloride

Abstract

We study, using wide-angle and small-angle light scattering techniques, the stability and aggregation/gelation behaviors of denatured filamentous bovine serum albumin pre-aggregates (BSA-PAs), induced by CaCl(2). It is observed that transparent filamentous gels can be formed not only at low CaCl(2) concentrations but also at high CaCl(2) concentrations, while turbid gels are obtained at intermediate CaCl(2) concentrations. Although the filamentous gels at low CaCl(2) concentrations and the turbid gels at intermediate CaCl(2) concentrations are consistent with the literature observations, the filamentous gels at high CaCl(2) concentrations have to be explained by different mechanisms. The latter is attributed to the repulsive hydration interactions originating from increased surface dipoles generated by counterion binding. Since such surface dipole-induced hydration is very short-range and occurs mainly on charged or polar patches of proteins (thus protected from aggregation), the aggregation of the filamentous BSA-PAs at hydrophobic patches at the two ends is still possible, leading to formation of the filamentous gels.

Sulfate Anion Delays the Self-Assembly of Human Insulin by Modifying the Aggregation Pathway

“…Ions and other cosolutes, such as sugars, polyols, and amino acids, mediate protein intra-and intermolecular interactions via a combination of several effects such as charge screening, ion binding, preferential exclusion, and dipole interactions, therefore affecting the protein secondary and quaternary structure (14)(15)(16)(17)(18)(19) as well as the individual microscopic events underlying the aggregation process (20). Peculiar effects such as ion specificity and restabilization behavior at large salt concentrations have been observed in the aggregation of many different proteins, ranging from short peptides to globular multidomain proteins (21)(22)(23)(24)(25). In the amyloid field, specific ion effects have been observed for instance in the aggregation of the Ab peptide (26), a-synuclein (27), islet amyloid polypeptide (28), prion protein (29), and HypF-N (30).…”

Light Scattering – The Application of Static Light Scattering: Zimm Plot

“…Note that the obtained R g value should be independent of the particle concentration. In this case of BSA, the dn 0 /dc value has been well determined in the literature, 14,15 as being equal to 0.186 cm 3 g À1 . 14 Step 2: Perform Zimm plot I to obtain the average molecular weight and the second virial coefficient From eqn [17], to perform Zimm plot I, computing K and R ex (0) is required.…”

“…This approach has been applied to investigate the colloidal stability (B 2 ) of the BSA clusters mentioned earlier as a function of the CaCl 2 concentration, C s , and the results have been reproduced from the original work 14 in Figure 5 (open circles). A particularly interesting finding is that at low CaCl 2 concentration, the B 2 value decreases as C s increases, that is, as expected, the stability of the BSA clusters decreases as the CaCl 2 concentration increases.…”

“…In this way, the I ex (0) value, as well as the radius of gyration, R g , is obtained from the slope of the line. 14 Step 2: Perform Zimm plot I to obtain the average molecular weight and the second virial coefficient From eqn [17], to perform Zimm plot I, computing K and R ex (0) is required. Note that the obtained R g value should be independent of the particle concentration.…”

“…9 The general equation of the Zimm plot in this case can be obtained by substituting eqn [14] into eqn [6] to replace S(q) so as to have, after rearrangement, The above expansion is valid at not too high concentrations.…”