Lucia De Rosa

β-Hairpin Peptide That Targets Vascular Endothelial Growth Factor (VEGF) Receptors DESIGN, NMR CHARACTERIZATION, AND BIOLOGICAL ACTIVITY

VEGF receptors have been the target of intense research aimed to develop molecules able to inhibit or stimulate angiogenesis. Based on the x-ray structure of the complex placental growth factor-VEGF receptor 1D2, we designed a VEGF receptor-binding peptide reproducing the placental growth factor β-hairpin region Gln87–Val100 that is involved in receptor recognition. A conformational analysis showed that the designed peptide adopts the expected fold in pure water. Moreover, a combination of NMR interaction analysis and cell binding studies were used to demonstrate that the peptide targets VEGF receptors. The VEGF receptor 1D2-interacting residues were characterized at the molecular level, and they correspond to the residues recognizing the placental growth factor sequence Gln87–Val100. Finally, the peptide biological activity was characterized in vitro and in vivo, and it showed a VEGF-like behavior. Indeed, the peptide activated VEGF-dependent intracellular pathways, induced endothelial cell proliferation and rescue from apoptosis, and promoted angiogenesis in vivo. This compound is one of the few peptides known with proangiogenic activity, which makes it a candidate for the development of a novel peptide-based drug for medical applications in therapeutic angiogenesis.

Peptides Targeting Angiogenesis Related Growth Factor Receptors

Growth factors (GFs) are extracellular signaling polypeptides regulating cell proliferation, differentiation and survival. They exert a wide spectrum of biological activities selectively binding to and activating specific membrane receptors which then transfer the message to cell interior inducing specific biochemical pathways. GFs are especially involved in the regulation of angiogenesis, a physiological process underlining several pathologies. Molecules able to modulate angiogenesis, interfering with the molecular recognition between a GF and its receptor, have a big pharmacologic interest. Either GF and the receptor are potential drug target. Peptides are useful molecules to develop new lead compounds disrupting protein-protein interface for pharmacological applications. In this review we describe peptides targeting the receptors of the pro-angiogenic growth factors FGF, PDGF and VEGF. The biological function and the structure of each growth factor/receptor system are discussed, as well as the molecular interaction between peptides and the receptors. Finally, we highlight the pharmacological and diagnostic applications of these peptides in angiogenesis related diseases.

Functional Binding Surface of a β‐Hairpin VEGF Receptor Targeting Peptide Determined by NMR Spectroscopy in Living Cells

In this study, the functional interaction of HPLW peptide with VEGFR2 (Vascular Endothelial Growth Factor Receptor 2) was determined by using fast (15)N-edited NMR spectroscopic experiments. To this aim, (15)N uniformly labelled HPLW has been added to Porcine Aortic Endothelial Cells. The acquisition of isotope-edited NMR spectroscopic experiments, including (15)N relaxation measurements, allowed a precise characterization of the in-cell HPLW epitope recognized by VEGFR2.

Semi-Synthesis of Labeled Proteins for Spectroscopic Applications

Since the introduction of SPPS by Merrifield in the 60s, peptide chemists have considered the possibility of preparing large proteins. The introduction of native chemical ligation in the 90s and then of expressed protein ligation have opened the way to the preparation of synthetic proteins without size limitations. This review focuses on semi-synthetic strategies useful to prepare proteins decorated with spectroscopic probes, like fluorescent labels and stable isotopes, and their biophysical applications. We show that expressed protein ligation, combining the advantages of organic chemistry with the easy and size limitless recombinant protein expression, is an excellent strategy for the chemical synthesis of labeled proteins, enabling a single protein to be functionalized at one or even more distinct positions with different probes.

Structural investigation of the VEGF receptor interaction with a helical antagonist peptide

Angiogenesis is mainly regulated by the vascular endothelial growth factor (VEGF), a mitogen specific for endothelial cells, which binds two tyrosine kinase receptors, VEGFR1 and VEGFR2, on the surface of endothelial cells. Molecules targeting VEGF receptors are attractive to pharmacologically treat diseases associated with angiogenesis or to be used as probes in angiogenesis imaging. Recently, we reported a designed peptide targeting VEGF receptors and able to inhibit the VEGF‐angiogenic response in vitro and in vivo. In this study, we employed NMR and molecular modeling methodology to investigate the molecular determinants of the interaction peptide‐receptor. In particular, the peptide binding site on VEGFR1 domain 2 and the residues involved in receptor recognition have been determined. These results provide significant information to develop a new class of molecules able to recognize the VEGF receptors overexpressed in pathological angiogenesis. Copyright

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.

Long range Trp-Trp interaction initiates the folding pathway of a pro-angiogenic β-hairpin peptide

HPLW, a designed VEGF (Vascular Endothelium Growth Factor) receptor-binding peptide, assumes a well folded β-hairpin conformation in water and is able to induce angiogenesis in vivo. In this study, we investigated at atomic resolution the thermal folding/unfolding pathway of HPLW by means of an original multi-technique approach combining DSC, NMR, MD and mutagenesis analyses. In particular, careful NMR investigation of the single proton melting temperatures together with DSC analysis accurately delineate the peptide folding mechanism, which is corroborated by computational folding/unfolding simulations. The HPLW folding process consists of two main events, which are successive but do not superimpose. The first folding step initiates at 320 K upon the hydrophobic collapse of the Trp5 and Trp13 side-chains which stabilizes the concurrent β-turn formation, whose COi-HNi + 3 hydrogen bond (Asp10 → Arg7) appears particularly stable. At 316 K, once the β-turn is completely formed, the two β-strands pair, very likely starting by Trp5 and Trp13, which thus play a key role also in the final step of the β-hairpin folding. Overall, here we describe a multi-state hierarchical folding pathway of a highly structured β-hairpin, which can be classified as a broken-zipper mechanism.

Analysis of the haptoglobin binding region on the apolipoprotein A‐I‐derived P2a peptide

Apolipoprotein A‐I (ApoA‐I) is the main protein component of the high density lipoproteins and it plays an important role in the reverse cholesterol transport. In particular, it stimulates cholesterol efflux from peripheral cells toward liver and activates the enzyme lecithin‐cholesterol acyltransferase (LCAT). Haptoglobin (Hpt), a plasma α2‐glycoprotein belonging to the family of acute‐phase proteins, binds to ApoA‐I inhibiting the stimulation of the enzyme LCAT. Previously, we reported that a synthetic peptide, P2a, binds to and displaces Hpt from ApoA‐I restoring the LCAT cholesterol esterification activity in the presence of Hpt. Here, we investigate the molecular determinants underlining the interaction between Hpt and P2a peptide. Analysis of truncated P2a analogs showed that P2a sequence can only be slight reduced in length at the N‐terminal to preserve the ability of binding to Hpt. Binding assays showed that charged residues are not involved in Hpt recognition; actually, E146A and D157A substitutions increase the binding affinity to Hpt. Biological characterization of the corresponding P2a peptide analogs, Apo146 and Apo157, showed that the two peptides interfere with Hpt binding to HDL and are more effective than P2a peptide in rescue LCAT activity from Hpt inhibition. This result suggests novel hints to design peptides with anti‐atherogenic activity. Copyright

Structure and biological activity of a conformational constrained apolipoprotein A-I-derived helical peptide targeting the protein haptoglobin

The development of novel pharmacological treatments for atherosclerosis is an active research field in medicinal chemistry. It has been shown that the acute phase protein haptoglobin (Hpt) plays a role in modulating the reverse cholesterol transport binding to the HDL-major protein Apolipoprotein A-I, and it also plays a role in impairing the activity of the lecithin–cholesterol acyltransferase (LCAT). We reported that the peptide P2a in vitro and in vivo restores the LCAT activity in the presence of Hpt. Now, we have designed and characterized a conformational constrained P2a analogue, ApoAib, with the intention of improving Hpt binding and metabolic stability. Using non-proteogenic aminoisobutyric acid residues, we have obtained a well folded α-helical peptide with high proteolytic stability in serum. It binds to Hpt, impairs haptoglobin binding to HDL, and restores LCAT activity in the presence of haptoglobin. Furthermore, an interaction analysis using NMR revealed the peptide binding site involved in haptoglobin molecular recognition. In conclusion, ApoAib represents a promising candidate to improve reverse cholesterol transport for application in cardiovascular diseases.

VEGFR Recognition Interface of a Proangiogenic VEGF-Mimetic Peptide Determined In Vitro and in the Presence of Endothelial Cells by NMR Spectroscopy

QK peptide is a vascular endothelial growth factor (VEGF)-mimetic molecule with significant proangiogenic activity. In particular, QK is able to bind and activate VEGF receptors (VEGFRs) to stimulate a functional response in endothelial cells. To characterize the peptide bioactivity and its molecular recognition properties, a detailed picture of the interaction between peptide QK and VEGF receptors is reported. By combining NMR spectroscopy studies in solution on the purified receptor and in the presence of intact endothelial cells, a molecular description of the binding interaction between peptide QK and VEGFR2 in the cellular context is obtained. These results reveal useful insights into the peptide biological mechanism, which opens the way to further optimization of this class of VEGF-mimicking peptides.