Transformation of oligomers of lipidated peptide induced by change in pH.

Oligomerization of lipidated peptides is of general scientific interest and is important in biomedical and pharmaceutical applications. We investigated the solution properties of a lipidated peptide, Liraglutide, which is one of the glucagon-like peptide-1 (GLP-1) agonists used for the treatment of type II diabetes. Liraglutide can serve as a model system for studying biophysical and biochemical properties of micelle-like self-assemblies of the lipidated peptides. Here, we report a transformation induced in Liraglutide oligomers by changing pH in the vicinity of pH 7. This fully reversible transformation is characterized by changes in the size and aggregation number of the oligomer and an associated change in the secondary structure of the constituent peptides. This transformation has quite slow kinetics: the equilibrium is reached in a course of several days. Interestingly, while the transformation is induced by changing pH, its kinetics is essentially independent of the final pH. We interpreted these findings using a model in which desorption of the monomer from the oligomer is the rate-limiting step in the transformation, and we determined the rate constant of the monomer desorption.