Abstract

Exploring Protein-protein Interactions Using Scaffolded and Assembled Peptides as Synthetic Binding Site Mimics

Jutta Eichler, Professor, University of Erlangen-Nuremberg

The design and generation of peptides capable of mimicking the binding and/or functional sites of proteins, represents a promising strategy for the exploration and modulation of protein function through controlled interference with the underlying protein-ligand interactions.  We have recently designed a soluble synthetic peptide that functionally mimics the HIV-1 coreceptor CXCR4, which belongs to the family of seven-transmembrane GPCRs. This CXCR4 mimetic peptide, termed CX4-M1, presents the three extracellular loops (ECLs) of the receptor. In binding assays involving recombinant proteins, as well as in cellular infection assays, CX4-M1 was found to selectively recognize gp120 from HIV-1 strains that use CXCR4 for cellular entry (X4 tropic HIV-1). Furthermore, anti-HIV-1 antibodies modulate this interaction in a molecular mechanism related to that of their impact on the gp120-CXCR4 interaction. We could now show that the selectivity of CX4-M1 pertains not only to gp120 from X4 tropic HIV-1, but also to synthetic peptides presenting the V3 loops of these gp120 proteins. The V3 loop is thought to be an essential part of the coreceptor binding site of gp120 that contacts the second ECL of the coreceptor. We were able to experimentally confirm this notion in binding assays using substitution analogs of CX4-M1 and the V3 loop peptides, respectively, as well as in cellular infection assays.  These results demonstrate the feasibility of mimicking protein-protein interactions through peptide-peptide interactions, as well as the utility of these mimetic peptides to explore protein-protein interactions at the molecular level.