On antisense peptides: the parathyroid hormone as an experimental example and a critical theoretical view

Peptide self-aggregation and peptide complementarity as bases for the evolution of peptide receptors: a review

This paper reviews the three major theories of peptide receptor evolution: (1) Dwyer's theory that peptide receptors evolved from self-aggregating peptides; (2) Root-Bernstein's theory that peptide receptors evolved from functionally and structurally complementary peptides; and (3) Blalock's theory that receptors evolved from hydropathically complementary sequences encoded in the antisense strand of the DNA encoding each peptide. The evidence to date suggests that the co-yevolution of peptides and their receptors is strongly constrained by one or more of these physicochemically based mechanisms, which argues against a random or frozen accident' model. The data also suggest that structure and function are integrally related from the earliest steps of receptor-ligand evolution so that peptide functionality is non-random and highly conserved in its origin. The result is a molecular paleontology' that reveals the evolutionary constraints that shaped the interaction of structure and function.

Rational design of peptide vaccines for autoimmune disease: harnessing molecular recognition to fix a broken network

Autoreactive T-cells and antibodies are found at low levels in normal individuals and are thought to be kept at bay by regulatory T-cells and a network of idiotypic and anti-idiotype-bearing antigen receptors on lymphocytes as well as idiotypic anti-idiotypic antibodies. Disruption of this network by genetic, environmental and unknown factors is thought to result in autoimmune diseases. An obvious, ideal and specific therapy for such disorders would be to harness this regulatory network to re-establish immunologic homeostasis. In practice, however, this is not an easy task as most autoimmune diseases involve polyclonal responses to self antigen. Thus, we are faced with the conundrum of not knowing which autoreactive idiotype-bearing antibody or antigen receptor(s) to target in order to restore or induce network regulatory function. The thesis of this review is that understanding a fundamental property governing peptide/protein shape can be used in part to circumvent the problems of self reactivity and polyclonality in autoimmune disorders. More specifically, an algorithm has been developed to design peptide vaccines with shapes that are thought to be complementary in contour to self epitopes which seem to be the focus of autoimmunity. In theory, such complementary shapes should be engendered in certain autoreactive antigen receptors--these complementary constructs consequently represent receptor mimetics. By targeting an immune response against such mimetics, one generates a polyclonal anti-idiotype response that matches the complexity of the autoimmune response itself. This article will describe the algorithm for vaccine design, summarize the in vitro and in vivo evidence for its efficacy and discuss possible therapeutic utility in human autoimmune diseases.

Molecular complementarity III. peptide complementarity as a basis for peptide receptor evolution: a bioinformatic case study of insulin, glucagon and gastrin

Dwyer has suggested that peptide receptors evolved from self-aggregating peptides so that peptide receptors should incorporate regions of high homology with the peptide ligand. If one considers self-aggregation to be a particular manifestation of molecular complementarity in general, then it is possible to extend Dwyer's hypothesis to a broader set of peptides: complementary peptides that bind to each other. In the latter case, one would expect to find homologous copies of the complementary peptide in the receptor. Thirteen peptides, 10 of which are not known to self-aggregate (amylin, ACTH, LHRH, angiotensin II, atrial natriuretic peptide, somatostatin, oxytocin, neurotensin, vasopressin, and substance P), and three that are known to self-aggregate (insulin, glucagon, and gastrin), were chosen. In addition to being self-aggregating, insulin and glucagon are also known to bind to each other, making them a mutually complementary pair. All possible combinations of the 13 peptides and the extracellular regions of their receptors were investigated using bioinformatic tools (a total of 325 combinations). Multiple, statistically significant homologies were found for insulin in the insulin receptor; insulin in the glucagon receptor; glucagon in the glucagon receptor; glucagon in the insulin receptor; and gastrin in gastrin binding protein and its receptor. Most of these homologies are in regions or sequences known to contribute to receptor binding of the respective hormone. These results suggest that the Dwyer hypothesis for receptor evolution may be generalizable beyond self-aggregating to complementary peptides. The evolution of receptors may have been driven by small molecule complementarity augmented by modular evolutionary processes that left a "molecular paleontology" that is still evident in the genome today. This "paleontology" may allow identification of peptide receptor sites.

Inhibition of HIV-1 infection by an intramolecular antisense peptide to T20 in gp160

Antisense amino acids are amino acids which can be translated from the corresponding anti-codons of a sense amino acid. Antisense peptides encoded by the noncoding DNA strand have a tendency to interact with each other. We have demonstrated that antisense peptide sequences are present intramolecularly, and these may contribute to the folding and maintenance of the tertiary structure of a protein. T20 is a synthetic peptide with an amino acid sequence in the gp41 of HIV-1 and has been demonstrated to be a potent inhibitor of HIV-1 infection. We searched for intramolecular peptide sequences which are antisense to portions of T20. A synthetic peptide (TA-1L) consisting of amino acids 84 to 97 of gp160, which contains an antisense peptide sequence (TA-1) to T20, was shown to inhibit HIV-1(IIIB) infection of MT-4 cells. Interaction of these antisense peptides could be involved in sustaining HIV-1 infectivity. The TA-1L site, which exists in the C1 domain of gp160, is highly homologous among strains of HIV-1, especially at TA-1 and in the amino acids flanking the C terminus. Although the TA-1 sites of 18 out of 30 HIV-1 strains were antisense to the T20 region, those of the remaining 12 strains, including HIV-1(MN), were not. However, TA-1L inhibited infection by HIV-1(MN), which has no antisense peptide in T20 corresponding to TA-1, although the inhibitory effect was weaker. TA-1L may thus also interfere with the gp160 interaction with CD4, which has an antisense sequence to TA-1.

Antisense peptide interactions studied by electrospray ionization mass spectrometry

Non-covalent interactions between met- and leu-enkephalins and their antisense peptides were studied by electrospray ionization mass spectrometry. Mixtures of sense and antisense peptides gave both the corresponding homodimers and heterodimers. The relative abundance ratios of the heterodimer to that of the homodimer of the sense peptide and the relative stability constants of the heterodimers were compared with the corresponding values from mixtures of the sense peptides and a control peptide. The results show that there is a preferential interaction between the sense and antisense peptides compared with that between the sense and control peptides.

Augmentation of aortic ring contractions by angiotensin II antisense peptide

Previous biochemical experiments have revealed two antisense peptide antagonists to human angiotensin II (Ang II), one encoded in the cDNA in the antiparallel reading, the other in the parallel reading. Neither peptide's ability to produce physiological antagonism has been demonstrated previously. Both peptides were tested for their ability to antagonize Ang II-induced contractions on rabbit aorta smooth muscle. Neither peptide had any direct contractile activity. The antiparallel Ang II peptide had physiological antagonism to Ang II contractions at a lower sensitivity than reported in biochemical studies, and its antagonist activity was partially blocked by Ang II antiserum, suggesting that it is not an antipeptide but an Ang II homologue. The parallel Ang II antipeptide also required high concentrations for physiological inhibition. Its contractile inhibition was not affected by Ang II antiserum and diminished the Ang II contraction at high micromolar concentrations, findings consistent with physicochemical data showing that it is an Ang II complement. The concentration of either peptide required to produce an antagonistic physiological effect was too high to predict any pharmacological usefulness. The parallel antipeptide, however, significantly increased the force of muscle contractions at high nanomolar concentrations, thus displaying a unique dual augmentation/antagonist activity. This antipeptide seems to have highly sequence-specific activity because other similar parallel antipeptides had no activity. The parallel antipeptide augmentation mimics the shift in the Ang II dose-response curve produced in hypertension studies of the slow pressor effect of Ang II and may be useful in deducing the currently unknown cause of the slow pressor effect. It may also have some uses in migraine studies.

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.

Studies on T-cell receptors involved in experimental autoimmune encephalomyelitis using the complementary peptide recognition approach

Based upon Blalock's complementary recognition approach, a complementary or antisense peptide (CP) was designed to the experimental autoimmune encephalomyelitis (EAE) epitope peptide, rat myelin basic protein (MBP) peptide 72-82. This peptide (EAE CP) was shown to have some sequence similarities to T-cell receptors (TCR) and MHC II molecules in a sequence homology search. Solid-phase binding assays demonstrated specific and high affinity binding (3 and 4 microM) between the EAE CP and the rat and guinea pig EAE epitope peptides (Rt72-82 and Gp69-82), respectively. This EAE CP was also found to be immunogenic in rats in an ear swelling test for delayed type hypersensitivity (DTH) reactions and an ELISA for antibody responses. However, a rabbit antibody generated to EAE CP was shown to be unable to stain the V beta 8+ EAE susceptible T-cells in immunofluorescence analyses. This EAE CP was also used in attempts to down-regulate EAE and the results showed that prior immunization with EAE CP in complete Freund's adjuvant could not prevent the Lewis rats from developing EAE. Although the data on sense-antisense peptide interaction were positive and the EAE CP was immunogenic, the inability of EAE CP to regulate EAE indicates that the CP approach may not be generally applicable.

Canine parietal cell binding by antibodies to the complementary peptide of somatostatin

Using antibodies to a complementary peptide of somatostatin, putative somatostatin binding proteins were characterized on canine parietal cells. A synthetic peptide (S-C1) was derived from the complementary mRNA sequence for somatostatin-14. Antiserum containing antibodies to S-C1 inhibited competitively 125I-Tyr11-somatostatin binding to canine oxyntic mucosal membranes. Canine parietal cell preparations were incubated with carbachol in the presence or absence of somatostatin and antisera to S-C1. Antibodies to S-C1 produced a decrease in carbachol-stimulated 14C-aminopyrine uptake comparable with that produced by 10(-6) M somatostatin. In immunocytochemical studies by light microscopy, antibodies to S-C1 produced positive staining of parietal cells throughout the oxyntic gland area. By electron microscopy using immunogold techniques, binding by antibodies to somatostatin C-1 was localized ultrastructurally to basolateral and intracellular membranes and to secretory canalicular membranes of parietal cells. These studies support the conclusion that antibodies to the somatostatin complementary peptide demonstrate properties similar to those of somatostatin in that they inhibit carbachol-stimulated aminopyrine uptake and 125I-somatostatin binding. Furthermore, these antibodies localize to specific regions on plasma membranes of parietal cells, which may represent somatostatin binding sites.

Lack of interaction of vasopressin with its antisense peptides: a functional and immunological study

The peptide encoded in the 5' to 3' direction by rat vasopressin complementary RNA, rat PVA (H-Ser-Ser-Trp-Ala-Val-Leu-Glu-Val-Ala- OH) and the corresponding bovine PVA (H-Ala-Pro-Trp-Ala-Val-Leu-Glu-Val-Ala-OH) were investigated with respect to their interaction with [8-arginine] vasopressin (AVP) and V2 vasopressin receptor binding and function. Rat or bovine PVA did neither affect the binding of the hormone to the V2 receptor of bovine kidney membranes and LLC-PK1 pig kidney cells nor influence the AVP-induced cAMP-production in LLC-PK1 cells. Rat PVA was further investigated by the use of vasopressin-specific polyclonal and monoclonal antibodies with different affinity and epitope specificity. Consistent with receptor binding studies no inhibition of [3H]AVP-binding in fluid- or solid-phase antibody binding tests after preincubation with PVA was found. Direct interaction of rat PVA and [3H]AVP measured on solid surface was not observed in contrast to specific binding of the hormone with NP II and antibodies. In our study no evidence for an interaction of AVP and its antisense peptides was found.

Critical evaluation of a theory of molecular recognition using human insulin-like-growth-factor-I fragment 21-40 and its complementary peptide

Using solid-phase methods we have synthesized human insulin-like-growth-factor-I (IGF-I) fragment 21-40 (IGF-I 21-40) and the peptide derived from the 5'----3' translation of the complementary nucleic acid of this peptide, 'I-FGI 20-40' (the complementary peptide). According to a recently proposed theory of molecular recognition, these two peptides should bind specifically to each other. We have tested this theory by using both solid- and solution-phase direct-binding assays for this complementary-peptide pair. We have also investigated the ability of I-FGI 20-40 to interfere with native IGF-I binding during radioimmunoassay (r.i.a.), radio-receptor (r.r.a.) assay and ligand-blot analysis of IGF-binding proteins. We have obtained no evidence of any interaction between IGF-I 21-40 and I-FGI 20-40 in either solid- or solution-phase assays. In addition, I-FGI 20-40 does not interfere in the assays used to detect IGF-I binding antibodies (r.i.a.), receptors (r.r.a.) or binding proteins (ligand blots). Our data therefore question the universality of this particular theory of molecular recognition.

Antagonist effect of a receptor-mimicking peptide encoded by human angiotensin II complementary RNA

This article reports on the binding and the angiotensin II (Ang II) antagonistic properties of a peptide, referred to as hIIA, encoded by an RNA strand complementary to the human Ang II messenger RNA. Although Ang II and hIIA (H2N-Glu-Gly-Val-Tyr-Val-His-Pro-Val-COOH) share four amino acids, the iodinated and tritiated forms of hIIA were unreactive with seven monoclonal antibodies defining four distinct epitopes on the Ang II molecule and failed to bind to Ang II hepatic and mesangial receptors. However, hIIA did inhibit binding of 125I-Ang II to rat hepatocyte membranes (IC50, 2 x 10(-7) M) and to the various monoclonal antibodies. The lowest IC50 (5 x 10(-7) M) was measured with the monoclonal antibody specific for the Ang II sequence generally considered as implicated in receptor recognition. As predicted from the binding studies, hIIA was further shown to antagonize some biological properties of Ang II. On mesangial cells, hIIA alone had no effect on intracellular calcium concentration ([Ca2+]i) and prostaglandin E2 synthesis but did abolish the transient increase in [Ca2+]i in response to 100 nM Ang II and did induce a specific dose-dependent inhibition of the Ang II-stimulated prostaglandin E2 release. Furthermore, intravenous infusion of hIIA (200 micrograms.kg-1.min-1) inhibited by 66 +/- 3% the rat hypertensive response to 100 ng.kg-1 Ang II but had no effect on the pressor activity of agents such as alpha 1-adrenergic and HT2 serotonin agonists. Our data suggest that the "complementary" peptide hIIA interacts directly with Ang II by mimicking the Ang II complementary site on the receptor and can inhibit the physiological effects of Ang II. This type of Ang II complementary peptide may serve as a model for a new class of antihypertensive drugs.

Affinity capture of [Arg8]vasopressin-receptor complex using immobilized antisense peptide

Solubilized noncovalent complexes of [Arg8]-vasopressin (AVP) with receptor proteins from rat liver membranes were isolated by selective binding to silica-immobilized antisense (AS) peptide. The affinity chromatographic support was prepared with a chemically synthesized AS peptide whose sequence is encoded by the AS DNA corresponding to the 20 amino-terminal residues of the AVP bovine neurophysin II biosynthetic precursor [pro-AVP/BNPII-(20-1)], a region that includes the AVP sequence at residues 1-9. The AVP-related AS peptide previously was shown to bind selectively to AVP. The AS peptide-AVP interaction mechanism hypothesized, contact by hydropathic complementarily at multiple sites along the peptide chains, led to the prediction that AVP bound to its receptor would still have enough free surface to interact with immobilized AS peptide. To test this prediction of a three-way interaction, [3H]AVP-receptor was obtained as a solubilized, partially purified fraction from rat liver membrane. When this fraction was eluted through AS pro-AVP/BNPII-(20-1) silica, a complex containing [3H]AVP was bound and separated from the major, unretarded membrane protein fraction as well as from free AVP. Chemical crosslinking of [3H]AVP complex, SDS/PAGE of the products, and analysis of gel slices by scintillation counting led to detection of two major radiolabeled bands of 31 and 38 kDa. Covalent labeling was blocked when unlabeled AVP was added as a competitor before crosslinking. A third radiolabeled protein band of 15 kDa was found when the receptor complex was solubilized from rat liver membranes in the absence of the protease inhibitor phenylmethylsulfonyl fluoride. Covalently crosslinked [3H]AVP complex also was bound to the AS peptide column; binding was blocked by competition with unlabeled AVP in the elution buffer. Since the AVP-linked 31- and 38-kDa proteins have the same apparent molecular mass on SDS/PAGE as found previously by photo-affinity labeling, we conclude that the AS peptide column has affinity-captured AVP-receptor complexes. The 15-kDa protein appears to be an active AVP-receptor fragment of one or both of the larger proteins. It is generally concluded that immobilized AS peptides may be useful to isolate peptide and protein-receptor complexes in other systems as well.

Antisense peptides: tools for receptor isolation? Lack of antisense MSH and ACTH to interact with their sense peptides and to induce receptor-specific antibodies

The use of antisense peptides for receptor isolation as proposed by Blalock and his colleagues (e.g. TIBTECH 8, 140-144, 1990) was tested for human ACTH as well as alpha- and beta-MSH. We synthesized the corresponding antisense peptides HTCAh, HSM-alpha and HSM-beta and analyzed them for specific interaction with the sense peptides using several types of binding assay and bioassay. Similarly HTCAh antibodies were tested for binding to ACTH receptors and ACTH antibodies. All these experiments were negative, i.e. there was no specific interaction between sense and antisense peptides nor between the corresponding antibodies. Receptor binding of the sense peptides was not affected by the antisense peptides or HTCAh antibodies. Unexpectedly, HTCAh but not HSM-alpha or HSM-beta was a weak MSH agonist acting through a site independent of the MSH receptor. A detailed analysis of the concept of antisense peptides revealed that the theoretical background of the hypothesis of the 'molecular recognition theory' is rather weak, explaining the failure of various attempts to obtain specific receptor antibodies.

Is genetic code redundancy related to retention of structural information in both DNA strands?

We have noted that the sense-antisense relationships inherent in the genetic code divide the amino acids into three separate groups. The nature of the amino acids in each group may allow the polypeptides coded by the antisense strand to retain the secondary structure patterns of the translated strand. Also, this relationship requires all but eight of the codons in the eukaryotic code and all but four in the mitochondrial code. Thus, genetic code redundancy could be related to evolutionary pressure toward retention of protein structural information in both strands of DNA.

Conformational behavior of fragments of adrenocorticotropin and their antisense peptides determined by NMR spectroscopy and CD spectropolarimetry

An 'antisense' peptide ('HTCA'), whose sequence was generated by reading the antisense RNA sequence corresponding to ACTH (1-24) was shown to bind ACTH (1-24) with a Kd of 0.3 nM in a solid-matrix binding assay [( 1986) Biochem. J. 234, 679 683]. Two-dimensional NMR spectra were used to examine the conformational behavior in methanol and in water solution of two fragments of adrenocorticotropin, ACTH(1-24) and ACTH (1-13), as well as their antisense peptides, HTCA and HTCA(12-24). The conformations are extended chains in these solutions, both as isolated molecules and when mixed with their antisense complements. The Kd values are greater than 1 mM.