Modulation of protein-protein interactions by stabilizing/mimicking protein secondary structure elements

In view of the crucial role of protein-protein intercommunication both in biological and pathological processes, the search of modulators of protein-protein interactions (PPIs) is currently a challenging issue. The development of rational strategies to imitate key secondary structure elements of protein interfaces is complementary to other approaches based on the screening of synthetic or virtual libraries. In this sense, the present review provides representative examples of compounds that are able to disturb PPIs of therapeutic relevance, through the stabilization or the imitation of peptide hot-spots detected in contact areas of the interacting proteins. The review is divided into three sections, covering mimetics of the three main secondary structural elements found in proteins, in general, and in protein-protein interfaces, in particular (alpha-helices, beta-sheets, and reverse turns). Once the secondary element has been identified, the first approach typically involves the translation of the primary peptide structure into different cyclic analogues. This is normally followed by gradual decrease of the peptide nature through combination of peptide and non-peptide fragments in the same molecule. The final step usually consists in the development of pertinent organic scaffolds for appending key functional groups in the right spatial disposition, as a means towards totally non-peptide small molecule PPI modulators.