Protein aggregates can be stabilised by disulphide bridges. The whey protein b-lactoglobulin (b-lac) contains a disulphide bridge and a free cysteine that are shielded from the solvent by an a-helix. These groups are important in the thioldisulphide exchange that occurs during aggregation and gelation of b-lac. Replica exchange molecular dynamics simulations show that the exposure mechanism is very different for the two buried groups. While melting of the a-helix enhances exposure of the free cysteine, it does not for the buried bridge. These findings shed light on the molecular mechanism of the first step of b-lac denaturation and aggregation.
We report a numerical study of beta-lactoglobulin aggregation using grand canonical Monte Carlo simulations of a simple lattice model in which the proteins are represented by a single lattice point and interact via a sum of a short-ranged attraction, and a long-ranged screened electrostatic repulsion. For certain values of the potential parameters we observe the so-called cluster phase, in which protein aggregates of finite size repel each other. The properties of the cluster phase are dependent on the salt concentration, the charge of the protein, and the strength of the short-ranged attraction. Disulfide bridges are modeled by covalent bonds between the lattice points, and can exchange with free thiols. Allowing the thiol-disulfide exchange leads to a severe lowering in the chemical potential of the cluster transition, or equivalently, a lower monomer density. Moreover, we find that the disulfide bridges (or the free thiol groups) are not uniformly distributed over the aggregate. The free thiol groups are significantly more abundant on the surface than in the core of the aggregate, making the surface more reactive than the inner core. This finding might explain why films made of beta-lactoglobulin by cold gelation, after resolvation, reconstitute finite aggregates rather than a monomer solution.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.