Design of hydropathically complementary peptides for Big Endothelin affinity purification

Isolation of a novel basic FGF-binding peptide with potent antiangiogenetic activity

Basic fibroblast growth factor (bFGF), which plays an important role in tumour angiogenesis and progression, provides a potential target for cancer therapy. Here we screened a phage display heptapeptide library with bFGF and identified 11 specific bFGF-binding phage clones. Two of these clones had identical sequence and the corresponding peptide (referred to as P7) showed high homology to the immunoglobulin-like (Ig-like) domain III (D3) of high-affinity bFGF receptors, FGFR1 (IIIc) and FGFR2 (IIIc). The P7 peptide and its corresponding motif in D3 of FGFRs both carried negative charges and shared similar hydrophobic profiles. Functional analysis demonstrated that synthetic P7 peptides mediate strong inhibition of bFGF-induced cell proliferation and neovascularization. Our results demonstrate that the P7 peptide is a potent bFGF antagonist with strong antiangiogenetic activity, and might have therapeutic potential in cancer therapy.

Design, synthesis and screening of antisense peptide based combinatorial peptide libraries towards an aromatic region of SARS-CoV

A combination of high-performance affinity chromatography and antisense peptide based combinatorial peptide libraries was used to screen a potential inhibitor for SARS-CoV. An aromatic-amino acid-rich region within the transmembrane domain at the C terminal of spike (S) protein identified as a membrane-active region was chosen as the target sense peptide (SP) and immobilized as affinity ligand. Four antisense peptides were designed based on the degeneracy of genetic codes. One of them was screened as the lead peptide to construct the extended peptide libraries (EPL). The library screening was carried out at pH 5.5 so as to mimic the low-pH milieu required by virus fusion. After five cycles of screening, a dodecapeptide KKKKYRNIRRPG (DP) was identified to possess the highest binding affinity to the immobilized sense peptide. The dissociation constant of the complex between the DP and the SP was 5.64 x 10(-7) M in a physiological condition. The recognition between the DP and recombinant SARS S protein was demonstrated by ELISA assay to be in a saturable way. The competitive inhibition of the sense peptide in the competitive ELISA reveals the affinity binding between the DP and SARS S protein is specific and directed towards the target SP of the S protein. The results indicate this preferred polypeptide can be used as a lead compound of potent inhibitor of SARS-CoV. The mechanism study suggests the specific recognition between the DP and the target peptide was due to sequence-dependent and multi-modal affinity interaction.

Mechanistic Investigation into Complementary (Antisense) Peptide Mini-Receptor Inhibitors of Cytokine Interleukin-1

Sense peptides are coded for by the nucleotide sequence (read 5'-->3') of the sense (positive) strand of DNA. Conversely, a complementary peptide is coded for by the nucleotide sequence (read 5'-->3') of the complementary or antisense (negative) strand of DNA. In many instances, sense and corresponding complementary peptides have been observed to interact specifically. In order to study this process in more detail, longer, shorter and mutant variants of our original complementary peptide, VITFFSL, were synthesised and analysed for binding to and inhibition of cytokine human interleukin-1beta (IL- 1beta) in vitro. The behaviour of all peptides studied is discussed in terms of the Mekler- dlis (M-1) pair theory, a theory that accounts for specific sense-complementary peptide interactions in terms of through-space interactions between corresponding pairs of amino acid residues (M-1 pairs)] specified by the genetic code and its complement.

A monoclonal antibody directed against the neurokinin-1 receptor contains a peptide sequence with similar hydropathy and functional properties to substance P, the natural ligand for the receptor

Monoclonal antibody (mAb) PS12, obtained using the complementary peptide methodology, mimics the neuropeptide substance P (SP) in recognizing the SP-binding domain of the neurokinin-1 receptor (NK1R) and eliciting production of polyclonal antibodies cross-reacting with SP with a high affinity (Déry et al., 1997. J. Neuroimmunol. 76, 1-9). The aim of the present study was to investigate which structural features of mAb PS12 might account for this molecular mimicry. Cloning and sequencing of variable regions of both light (VL) and heavy (VH) chains of this 'SP-like' antibody did not indicate any primary sequence homology between SP and any antibody region. Instead, they revealed a striking similarity between the hydropathic profile of SP and that of an 11-amino-acid region in the light chain encompassing the second complementarity determining region (CDR2). When applied to CHO cells expressing the human NK1R, a synthetic extended 17-amino-acid peptide (denoted CDR2L) corresponding to this VL region inhibited the high-affinity binding of radiolabeled SP and antagonized the SP-induced inositol phosphate production. Moreover, a re-examination of the sequences of several antibodies that previously served in the design of CDR-derived bioactive peptides indicated that these antibodies also carried the hydropathic image of the respective ligands that they mimic. In agreement with previous observations on artificial synthetic peptides, our data thus suggest that the molecular mimicry between natural proteins (i.e. antibody and hormone, for example) could be understood on a structural level directly related, at least in part, to hydropathic homology. These results could then guide the search for bioactive paratope-derived peptides of potential pharmacological interest. We also observed inverse hydropathy between multiple CDRs of mAb PS12 (including CDR3H and CDR3L) and the peptide epitope, confirming the importance of hydropathic complementarity in antigen-antibody interactions.

Synthetic complementary peptides inhibit a neutrophil chemoattractant found in the alkali-injured cornea

PURPOSE

We have previously presented evidence that the neutrophil chemoattractant, N-acetyl-proline-glycine-proline (N-acetyl-PGP), triggers the initial polymorphonuclear leukocyte (PMN) invasion into the alkali-injured eye. In this study, sense-antisense methodology was used to develop novel complementary peptides to be potential inhibitors of N-acetyl-PGP.

METHODS

The polarization assay was used to measure the potential chemotactic response of PMNs to synthetic N-acetyl-PGP, the ultrafiltered tripeptide chemoattractants obtained from alkali-degraded rabbit corneas, or leukotriene B4 (LTB4). Inhibition was expressed as the peptide concentration producing 50% inhibition (ID50) of polarization. Five complementary peptides were tested as potential inhibitors of N-acetyl-PGP: arginine-threonine-arginine (RTR), RTR-glycine-glycine (RTRGG), RTR dimer, RTR tetramer, and alanine-serine-alanine (ASA) tetramer. In addition, the RTR tetramer and both monomeric peptides (RTR and RTRGG) were separately tested for inhibition of the ultrafiltered tripeptide chemoattractants or LTB4.

RESULTS

The complementary RTR tetrameric peptide was a powerful antagonist of N-acetyl-PGP-induced PMN polarization (ID50 of 200 nM). The RTR dimer was much less potent (ID50 of 105 microM). Both monomeric peptides, RTR and RTRGG, were only antagonistic at millimolar concentrations. The ASA tetramer showed no capacity to inhibit N-acetyl-PGP. The RTR tetramer also inhibited PMN activation by the ultrafiltered tripeptide chemoattractants (ID50 of 30 microM) but had no effect on LTB4.

CONCLUSIONS

A complementary peptide (RTR) was designed which is an effective inhibitor of the neutrophil chemoattractant, N-acetyl-PGP. The potency of the RTR complementary peptide is dramatically enhanced by tetramerization. Inhibition of N-acetyl-PGP by complementary peptides offers great promise for control of the inflammatory response in the alkali-injured eye.

A neuronal C5a receptor and an associated apoptotic signal transduction pathway

1. We report the first experimental evidence of a neuronal C5a receptor (nC5aR) in human cells of neuronal origin. Expression of nC5aR mRNA was demonstrated by the reverse transcriptase-polymerase chain reaction (RT-PCR) in TGW human neuroblastoma cells. 2. Expression of a functional C5aR was supported by the finding that C5a evoked a transient increase in the intracellular calcium level as measured by flow cytometry (FACS). 3. To analyse the function of the nC5aR, an antisense peptide fragment of the C5aR was used. Previous data showed that a C5aR fragment (a peptide termed PR226) has C5aR agonist and antagonist effects in U-937 cells depending on the concentration of the peptide. We found that a multiple antigenic peptide (MAP) form of the same peptide (termed PR226-MAP) induced rapid elevation of nuclear c-fos immunoreactivity and resulted in DNA fragmentation, a characteristic sign of apoptosis, in TGW cells. 4. Early electrophysiological events characteristic of apoptosis were also detected: intermittent calcium current pulses were recorded within 1-2 min of peptide administration. C5a pretreatment delayed the onset of this calcium influx. 5. We also demonstrated that the apoptotic pathway is linked to nC5aR via pertussis toxin-sensitive G-proteins. 6. Although the function of C5a and its receptor on neurons is unknown, these results suggest that an abnormal activation of this signal transduction pathway can result in apoptosis and, subsequently, in neurodegeneration.

Antisense homology box-derived peptides represent a new class of endothelin receptor inhibitors

Several peptides encoded by the sense and corresponding antisense DNA have been found to recognize and bind to each other. We developed software to search for sense-antisense regions within proteins taking into account the degeneracy of the genetic code, i.e., one amino acid can have several "antisense" counterparts. Using this approach, we searched endothelin receptor type A for intramolecular regions related in sense-antisense fashion. After locating these regions (termed "antisense homology boxes"), several corresponding peptides were synthesized. The four new ET(A) receptor fragment peptides ETR-P1 ("CALSVDRYRAVASW"), ETR-P3 ("QGIGPLITAIEI"), ETR-P4 ("IADNAERYSANLSSHV") and ETR-P6 ("LNRRNGSLRIALSEHLKNRREVA") reported here can inhibit ET-1 activity.

The antisense homology box: a new motif within proteins that encodes biologically active peptides

Amphiphilic peptides approximately fifteen amino acids in length and their corresponding antisense peptides exist within protein molecules. These regions (termed antisense homology boxes) are separated by approximately fifty amino acids. Because many sense-antisense peptide pairs have been reported to recognize and bind to each other, antisense homology boxes may be involved in folding, chaperoning and oligomer formation of proteins. The antisense homology box-derived peptide CALSVDRYRAVASW, a fragment of human endothelin A receptor, proved to be a specific inhibitor of endothelin peptide (ET-1) in a smooth muscle relaxation assay. The peptide was able to block endotoxin-induced shock in rats as well. Our finding of endothelin receptor inhibitor among antisense homology box-derived peptides indicates that searching proteins for this new motif may be useful in finding biologically active peptides.

Sequence-directed recognition peptides: inhibition of endothelin generation via a substrate-depletion mechanism

Sequence-directed recognition peptides (SDRPs) were constructed on the basis of their hydropathic complementarity for big-endothelin (bigET). These peptides can inhibit in vitro the proteolytic cleavage that generates endothelin (ET) from its bigET precursor. Comparison of dissociation constants of the complexes SDRP:bigET with kinetic constants obtained for the cleavage of bigET by alpha-chymotrypsin (taken as a model proteinase) provides evidence of the potential of SDRPs. This is a novel application of SDRPs used as inhibitors of a proteolytic reaction.

Affinity enhancement of complementary peptide recognition

A peptide hydropathically complementary to Big Endothelin [Big ET] residues 16-29 has been synthesized in a multimeric form starting from an octadentate polylysine core, essentially in a way similar to the procedure used for the production of multiple antigenic peptides [MAP's]. Interaction between the multimeric complementary peptide [8 delta ET] and the Big ET fragment 16-32 containing the target complementary region, also synthesized in a multimeric form [8ET], was evaluated by analytical high performance affinity chromatography and solid phase binding assays. While the binding interaction between the monomerics peptide pair was in the micromolar range, the recognition between the corresponding multimeric form was characterized by enhanced binding affinity of at least two orders of magnitude. In solution, complex formation between multimeric complementary peptide and target Big ET sequence in the monomeric and multimeric form was accompanied by precipitation at concentrations higher than 0.5 mg/mL and 0.1 mg/mL, respectively. Polyclonal antibodies raised against the multimeric target sequence recognized multimeric and monomeric ET target sequences with binding affinities similar to binding affinities exhibited by the multimeric complementary peptide. Multimerization of hydropathically complementary peptides could provide an improved opportunity to measure and thus probe quantitative binding properties of complementary peptides.