HIV-derived peptide mimics

Miniaturizing VEGF: Peptides mimicking the discontinuous VEGF receptor-binding site modulate the angiogenic response

The angiogenic properties of VEGF are mediated through the binding of VEGF to its receptor VEGFR2. The VEGF/VEGFR interface is constituted by a discontinuous binding region distributed on both VEGF monomers. We attempted to reproduce this discontinuous binding site by covalently linking into a single molecular entity two VEGF segments involved in receptor recognition. We designed and synthesized by chemical ligation a set of peptides differing in length and flexibility of the molecular linker joining the two VEGF segments. The biological activity of the peptides was characterized in vitro and in vivo showing a VEGF-like activity. The most biologically active mini-VEGF was further analyzed by NMR to determine the atomic details of its interaction with the receptor.

Ligand selectivity of a synthetic CXCR4 mimetic peptide

The chemokine receptor CXCR4 belongs to the family of seven-transmembrane G-protein coupled receptors (GPCRs). It is activated by its natural ligand SDF-1α. In addition, CXCR4, along with CCR5, serve as coreceptors during HIV-1 entry into its target cell. Recently, we introduced a CXCR4 mimetic peptide, termed CX4-M1, which presents the three extracellular loops (ECLs) of the receptor. CX4-M1 was shown to selectively bind to gp120 of X4-tropic, that is, CXCR4 using, HIV-1, as well as to peptides that present the V3-loops of these gp120 proteins. Furthermore, CX4-M1 selectively inhibits infection of cells with X4-tropic HIV-1. We have now adapted the sequence of the ECLs presented by CX4-M1 to the recently published crystal structure of CXCR4. The binding behavior, as well as the effect on HIV-1 infection, of the resulting peptide (CX4-Mc) was very similar to CX4-M1, validating retrospectively the original design of CX4-M1. A peptide presenting the ECLs of CCR5 (CR5-M), on the other hand, did neither bind to gp120 from X4-tropic HIV-1, nor did it inhibit infection of cells with X4-tropic HIV-1. Furthermore, we could show that CX4-M1, as well as CX4-Mc, but not CR5-M, are selectively recognized by anti-CXCR4 antibodies, bind to SDF-1α, and also inhibit SDF-1α signaling, extending the scope of selective functional CXCR4 mimicry through CX4-M1.

Enhancement and induction of HIV-1 infection through an assembled peptide derived from the CD4 binding site of gp120

Contact between the human immunodeficiency virus (HIV-1) and its target cell is initiated by the interaction of viral gp120 with cellular CD4. An assembled peptide (CD4bs-M) that presents the CD4 binding site of gp120 was previously shown to inhibit the gp120-CD4 interaction. Here, we demonstrate that CD4bs-M selectively enhances infection of cells with HIV-1, whereas infection with herpes simplex virus remains largely unaffected. The effects of CD4bs-M variants containing D-amino acids, or prolines at selected positions, point to the importance of side chain orientation and spatial orientation of this fragment. Furthermore, CD4bs-M was shown to assemble into amyloid-like fibrils that capture HIV-1 particles, which likely contributes to the infection-enhancing effect. Beyond infection enhancement, CD4bs-M enabled HIV-1 infection of CD4-negative cells, suggesting that binding of the peptide to gp120 facilitates interaction of gp120 with coreceptors, which might in turn enhance HIV-1 entry.

Mimicking Protein-Protein Interactions through Peptide-Peptide Interactions: HIV-1 gp120 and CXCR4

We have recently designed a soluble synthetic peptide that functionally mimics the HIV-1 coreceptor CXCR4, which is a chemokine receptor that 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 cell 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 indicate that interactions of the HIV-1 Env with coreceptors can be mimicked by synthetic peptides, which may be useful to explore these interactions at the molecular level in more detail.