De novo design of peptides targeted to the EF hands of calmodulin

Calmodulin Binding Activates Chromobacterium CopC Effector to ADP-Riboxanate Host Apoptotic Caspases

Blocking host cell death is an important virulence strategy employed by many bacterial pathogens. We recently reported that Shigella flexneri inhibits host pyroptosis by delivering a type III secretion system (T3SS) effector OspC3 that catalyzes a novel arginine ADP-riboxanation modification on caspase-4/11. Here, we investigated the OspC3 homologue CopC from Chromobacterium violaceum, an opportunistic but sometimes deadly bacterial pathogen. CopC bears the same arginine ADP-riboxanase activity as OspC3, but with a different substrate specificity. Through proteomic analysis, we first identified host calmodulin (CaM) as a binding partner of CopC. The analyses additionally revealed that CopC preferably modifies apoptotic caspases including caspase-7, -8 and -9. This results in suppression of both extrinsic and intrinsic apoptosis programs in C. violaceum-infected cells. Biochemical reconstitution showed that CopC requires binding to CaM, specifically in the calcium-free state, to achieve efficient ADP-riboxanation of the caspases. We determined crystal structure of the CaM-CopC-CASP7 ternary complex, which illustrates the caspase recognition mechanism and a unique CaM-binding mode in CopC. Structure-directed mutagenesis validated the functional significance of CaM binding for stimulating CopC modification of its caspase substrates. CopC adopts an ADP-ribosyltransferase-like fold with a unique His-Phe-Glu catalytic triad, featuring two acidic residues critical for site-specific arginine ADP-riboxanation. Our study expands and deepens our understanding of the OspC family of ADP-riboxanase effectors.

Calmodulin Bidirectionally Regulates Evoked and Spontaneous Neurotransmitter Release at Retinal Ribbon Synapses

For decades, a role for the Ca²⁺-binding protein calmodulin (CaM) in Ca²⁺-dependent presynaptic modulation of synaptic transmission has been recognized. Here, we investigated the influence of CaM on evoked and spontaneous neurotransmission at rod bipolar (RB) cell→AII amacrine cell synapses in the mouse retina. Our work was motivated by the observations that expression of CaM in RB axon terminals is extremely high and that [Ca²⁺] in RB terminals normally rises sufficiently to saturate endogenous buffers, making tonic CaM activation likely. Taking advantage of a model in which RBs can be stimulated by expressed channelrhodopsin-2 (ChR2) to avoid dialysis of the presynaptic terminal, we found that inhibition of CaM dramatically decreased evoked release by inhibition of presynaptic Ca channels while at the same time potentiating both Ca²⁺-dependent and Ca²⁺-independent spontaneous release. Remarkably, inhibition of myosin light chain kinase (MLCK), but not other CaM-dependent targets, mimicked the effects of CaM inhibition on evoked and spontaneous release. Importantly, initial antagonism of CaM occluded the effect of subsequent inhibition of MLCK on spontaneous release. We conclude that CaM, by acting through MLCK, bidirectionally regulates evoked and spontaneous release at retinal ribbon synapses.

Targeting Aquaporin-4 Subcellular Localization to Treat Central Nervous System Edema

Swelling of the brain or spinal cord (CNS edema) affects millions of people every year. All potential pharmacological interventions have failed in clinical trials, meaning that symptom management is the only treatment option. The water channel protein aquaporin-4 (AQP4) is expressed in astrocytes and mediates water flux across the blood-brain and blood-spinal cord barriers. Here we show that AQP4 cell-surface abundance increases in response to hypoxia-induced cell swelling in a calmodulin-dependent manner. Calmodulin directly binds the AQP4 carboxyl terminus, causing a specific conformational change and driving AQP4 cell-surface localization. Inhibition of calmodulin in a rat spinal cord injury model with the licensed drug trifluoperazine inhibited AQP4 localization to the blood-spinal cord barrier, ablated CNS edema, and led to accelerated functional recovery compared with untreated animals. We propose that targeting the mechanism of calmodulin-mediated cell-surface localization of AQP4 is a viable strategy for development of CNS edema therapies.

Functional peptide-based drug delivery systems

Peptides are one of the most important functional motifs for constructing smart drug delivery systems (DDSs). Functional peptides can be conjugated with drugs or carriers via covalent bonds, or assembled into DDSs via supramolecular forces, which enables the DDSs to acquire desired functions such as targeting and/or environmental responsiveness. In this mini review, we first introduce the different types of functional peptides that are commonly used for constructing DDSs, and we highlight representative strategies for designing smart DDSs by using functional peptides in the past few years. We also state the challenges of peptide-based DDSs and come up with prospects.

Cdc42 activation couples fluid shear stress to apical endocytosis in proximal tubule cells

Cells lining the kidney proximal tubule (PT) respond to acute changes in glomerular filtration rate and the accompanying fluid shear stress (FSS) to regulate reabsorption of ions, glucose, and other filtered molecules and maintain glomerulotubular balance. Recently, we discovered that exposure of PT cells to FSS also stimulates an increase in apical endocytic capacity (Raghavan et al. PNAS, 111:8506–8511, 2014). We found that FSS triggered an increase in intracellular Ca²⁺ concentration ([Ca²⁺]_i) that required release of extracellular ATP and the presence of primary cilia. In this study, we elucidate steps downstream of the increase in [Ca²⁺]_i that link FSS‐induced calcium increase to increased apical endocytic capacity. Using an intramolecular FRET probe, we show that activation of Cdc42 is a necessary step in the FSS‐stimulated apical endocytosis cascade. Cdc42 activation requires the primary cilia and the FSS‐mediated increase in [Ca²⁺]_i. Moreover, Cdc42 activity and FSS‐stimulated endocytosis are coordinately modulated by activators and inhibitors of calmodulin. Together, these data suggest a mechanism by which PT cell exposure to FSS is translated into enhanced endocytic uptake of filtered molecules.

On BH3 Mimetics and Ca2+ Signaling

Preclinical Research

BH3 mimetics are anticancer agents that reproduce the spatial arrangement of the BH3 domain of Bcl‐2 family proteins. Just like the BH3‐only proteins, these compounds bind to the hydrophobic cleft of the pro‐survival Bcl‐2 members such as Bcl‐2 or Bcl‐xL, and disrupt their heterodimerization with pro‐apoptotic Bax or Bak, sensitizing cells to chemotherapy. In recent years, it has become clear that Bcl‐2 family proteins are engaged in regulation of intracellular Ca²⁺ homeostasis, including Ca²⁺ release from the intracellular stores as well as Ca²⁺ fluxes across the plasma membrane. Given that BH3 mimetics shift the balance between the prosurvival and proapoptotic Bcl‐2 members, they might indirectly exert effects on intracellular Ca²⁺ signals. Indeed, it has been reported that some BH3 mimetics release Ca²⁺ from the intracellular stores causing Ca²⁺ overload in the cytosol. Therefore, the effects of any new BH3 mimetics on cellular Ca²⁺ homeostasis should be tested before these compounds progress to clinical trials. Drug Dev Res 78 : 313–318, 2017. © 2017 Wiley Periodicals, Inc.

Calmodulin is responsible for Ca2+-dependent regulation of TRPA1 Channels

TRPA1 is a Ca²⁺-permeable ion channel involved in many sensory disorders such as pain, itch and neuropathy. Notably, the function of TRPA1 depends on Ca²⁺, with low Ca²⁺ potentiating and high Ca²⁺ inactivating TRPA1. However, it remains unknown how Ca²⁺ exerts such contrasting effects. Here, we show that Ca²⁺ regulates TRPA1 through calmodulin, which binds to TRPA1 in a Ca²⁺-dependent manner. Calmodulin binding enhanced TRPA1 sensitivity and Ca²⁺-evoked potentiation of TRPA1 at low Ca²⁺, but inhibited TRPA1 sensitivity and promoted TRPA1 desensitization at high Ca²⁺. Ca²⁺-dependent potentiation and inactivation of TRPA1 were selectively prevented by disrupting the interaction of the carboxy-lobe of calmodulin with a calmodulin-binding domain in the C-terminus of TRPA1. Calmodulin is thus a critical Ca²⁺ sensor enabling TRPA1 to respond to diverse Ca²⁺ signals distinctly.

BH3 mimetic-elicited Ca2+ signals in pancreatic acinar cells are dependent on Bax and can be reduced by Ca2+-like peptides

BH3 mimetics are small-molecule inhibitors of B-cell lymphoma-2 (Bcl-2) and Bcl-xL, which disrupt the heterodimerisation of anti- and pro-apoptotic Bcl-2 family members sensitising cells to apoptotic death. These compounds have been developed as anti-cancer agents to counteract increased levels of Bcl-2 proteins often present in cancer cells. Application of a chemotherapeutic drug supported with a BH3 mimetic has the potential to overcome drug resistance in cancers overexpressing anti-apoptotic Bcl-2 proteins and thus increase the success rate of the treatment. We have previously shown that the BH3 mimetics, BH3I-2' and HA14-1, induce Ca²⁺ release from intracellular stores followed by a sustained elevation of the cytosolic Ca²⁺ concentration. Here we demonstrate that loss of Bax, but not Bcl-2 or Bak, inhibits this sustained Ca²⁺ elevation. What is more, in the absence of Bax, thapsigargin-elicited responses were decreased; and in two-photon-permeabilised bax^-/- cells, Ca²⁺ loss from the ER was reduced compared to WT cells. The Ca²⁺-like peptides, CALP-1 and CALP-3, which activate EF hand motifs of Ca²⁺-binding proteins, significantly reduced excessive Ca²⁺ signals and necrosis caused by two BH3 mimetics: BH3I-2' and gossypol. In the presence of CALP-1, cell death was shifted from necrotic towards apoptotic, whereas CALP-3 increased the proportion of live cells. Importantly, neither of the CALPs markedly affected physiological Ca²⁺ signals elicited by ACh, or cholecystokinin. In conclusion, the reduction in passive ER Ca²⁺ leak in bax^-/- cells as well as the fact that BH3 mimetics trigger substantial Ca²⁺ signals by liberating Bax, indicate that Bax may regulate Ca²⁺ leak channels in the ER. This study also demonstrates proof-of-principle that pre-activation of EF hand Ca²⁺-binding sites by CALPs can be used to ameliorate excessive Ca²⁺ signals caused by BH3 mimetics and shift necrotic death towards apoptosis.

The Role of Adjuvants in the Efficacy of a Peptide Vaccine for Myasthenia Gravis

Myasthenia gravis (MG) and its animal model, experimental autoimmune (EA) MG, are caused by interference with neuromuscular transmission by autoantibodies against the nicotinic acetylcholine receptor (AChR) on muscle. Previously, we have shown that two peptides, denoted RhCA 67-16 and RhCA 611-001, designed to be complementary in structure to the main immunogenic region and the dominant Lewis rat T cell epitope (α-chain residues 100-116) of the AChR, respectively, are effective vaccines that prevent EAMG in rats by inducing anti-idiotypic/clonotypic antibodies (Ab) and lowering levels of AChR Ab. These studies employed keyhole limpet hemocyanin (KLH) as a carrier and complete Freunds adjuvant (CFA). In advance of a clinical trial the present study tested the efficacy of RhCA 611-001 when combined with different adjuvants that are approved for use in humans. Adjuvants chosen for comparison were incomplete Freunds adjuvant (IFA) and aluminum hydroxide (Alum). As a second goal we evaluated diphtheria toxin (DT) as an alternative carrier protein to KLH. Alum was found to be an effective adjuvant, particularly when used with the peptide conjugated to DT. This combination of carrier and adjuvant provided protection against EAMG comparable with that observed with CFA and KLH. Using enzyme-linked immunosorbent assays for Ab against RhCA 611-001, it was found that disease protection is qualitatively, but not quantitatively, related to the anti-peptide Ab response. Our results demonstrate a vaccine formulation that should be useful in the first soon-to-be-conducted clinical trials of peptide vaccines to specifically correct aberrant T and B cell responses in an autoimmune disease.

Characterization of the Interactions between Calmodulin and Death Receptor 5 in Triple-negative and Estrogen Receptor-positive Breast Cancer Cells: AN INTEGRATED EXPERIMENTAL AND COMPUTATIONAL STUDY

Activation of death receptor-5 (DR5) leads to the formation of death inducing signaling complex (DISC) for apoptotic signaling. Targeting DR5 to induce breast cancer apoptosis is a promising strategy to circumvent drug resistance and present a target for breast cancer treatment. Calmodulin (CaM) has been shown to regulate DR5-mediated apoptotic signaling, however, its mechanism remains unknown. In this study, we characterized CaM and DR5 interactions in breast cancer cells with integrated experimental and computational approaches. Results show that CaM directly binds to DR5 in a calcium dependent manner in breast cancer cells. The direct interaction of CaM with DR5 is localized at DR5 death domain. We have predicted and verified the CaM-binding site in DR5 being (354)WEPLMRKLGL(363) that is located at the α2 helix and the loop between α2 helix and α3 helix of DR5 DD. The residues of Trp-354, Arg-359, Glu-355, Leu-363, and Glu-367 in DR5 death domain that are important for DR5 recruitment of FADD and caspase-8 for DISC formation to signal apoptosis also play an important role for CaM-DR5 binding. The changed electrostatic potential distribution in the CaM-binding site in DR5 DD by the point mutations of W354A, E355K, R359A, L363N, or E367K in DR5 DD could directly contribute to the experimentally observed decreased CaM-DR5 binding by the point mutations of the key residues in DR5 DD. Results from this study provide a key step for the further investigation of the role of CaM-DR5 binding in DR5-mediated DISC formation for apoptosis in breast cancer cells.

SOCS1 Mimetics and Antagonists: A Complementary Approach to Positive and Negative Regulation of Immune Function

Suppressors of cytokine signaling (SOCS) are inducible intracellular proteins that play essential regulatory roles in both immune and non-immune function. Of the eight known members, SOCS1 and SOCS3 in conjunction with regulatory T cells play key roles in regulation of the immune system. Molecular tools such as gene transfections and siRNA have played a major role in our functional understanding of the SOCS proteins where a key functional domain of 12-amino acid residues called the kinase inhibitory region (KIR) has been identified on SOCS1 and SOCS3. KIR plays a key role in inhibition of the JAK2 tyrosine kinase, which in turn plays a key role in cytokine signaling. A peptide corresponding to KIR (SOCS1-KIR) bound to the activation loop of JAK2 and inhibited tyrosine phosphorylation of STAT1α transcription factor by JAK2. Cell internalized SOCS1-KIR is a potent therapeutic in the experimental allergic encephalomyelitis (EAE) mouse model of multiple sclerosis and showed promise in a psoriasis model and a model of diabetes-associated cardiovascular disease. By contrast, a peptide, pJAK2(1001-1013), that corresponds to the activation loop of JAK2 is a SOCS1 antagonist. The antagonist enhanced innate and adaptive immune response against a broad range of viruses including herpes simplex virus, vaccinia virus, and an EMC picornavirus. SOCS mimetics and antagonists are thus potential therapeutics for negative and positive regulation of the immune system.

The Ca(v)3.1 T-type calcium channel is required for neointimal formation in response to vascular injury in mice

AIMS

Restenosis is an undesirable consequence following percutaneous vascular interventions. However, the current strategy for preventing restenosis is inadequate. The aim of this study was to investigate the role of low-voltage gated T-type calcium channels in regulating vascular smooth muscle cell (VSMC) proliferation during neointimal formation.

METHODS AND RESULTS

Wire injury of mice carotid arteries resulted in neointimal formation in the wild-type and Ca(v)3.2(-/-) but not Ca(v)3.1(-/-) mice, indicating a critical role of Ca(v)3.1 in neointimal formation. In addition, we found a significant increase of Ca(v)3.1 mRNA and protein in injured arteries. Ca(v)3.1 knockout or knockdown (shCa(v)3.1) reduced VSMC proliferation. Since T-channels are expressed predominantly in the G(1) and S phases in VSMCs, we examined whether an abnormal G(1)/S transition was the cause of the reduced cell proliferation in shCa(v)3.1 VSMCs. We found a disrupted expression of cyclin E in shCa(v)3.1 VSMCs, and calmodulin agonist CALP1 partially rescued the defective cell proliferation. Furthermore, we demonstrated that infusion of NNC55-0396, a selective T-channel blocker, inhibited neointimal formation in wild-type mice.

CONCLUSION

Ca(v)3.1 is required for VSMC proliferation during neointimal formation, and blocking of Ca(v)3.1 may be beneficial for preventing restenosis.

A chemical genetic approach identifies piperazine antipsychotics as promoters of CNS neurite growth on inhibitory substrates

Injury to the central nervous system (CNS) can result in lifelong loss of function due in part to the regenerative failure of CNS neurons. Inhibitory proteins derived from myelin and the astroglial scar are major barriers for the successful regeneration of injured CNS neurons. Previously, we described the identification of a novel compound, F05, which promotes neurite growth from neurons challenged with inhibitory substrates in vitro, and promotes axonal regeneration in vivo (Usher et al., 2010). To identify additional regeneration-promoting compounds, we used F05-induced gene expression profiles to query the Broad Institute Connectivity Map, a gene expression database of cells treated with >1300 compounds. Despite no shared chemical similarity, F05-induced changes in gene expression were remarkably similar to those seen with a group of piperazine phenothiazine antipsychotics (PhAPs). In contrast to antipsychotics of other structural classes, PhAPs promoted neurite growth of CNS neurons challenged with two different glial derived inhibitory substrates. Our pharmacological studies suggest a mechanism whereby PhAPs promote growth through antagonism of calmodulin signaling, independent of dopamine receptor antagonism. These findings shed light on mechanisms underlying neurite-inhibitory signaling, and suggest that clinically approved antipsychotic compounds may be repurposed for use in CNS injured patients.

Molecular recognition theory and sense-antisense interaction: therapeutic applications in autoimmunity

Perhaps behind only the understanding of the genetic code in importance is the comprehension of protein sequence and structure in its effect on modern scientific investigation. How proteins are structured and interact dictates a considerable amount of the body's processes in maintaining homeostasis. Unfortunately, in diseases of autoimmunity, these processes are directed against the body itself and most of the current clinical responses are severely lacking. This review addresses current therapeutics involved in the treatment of various autoimmune diseases and details potential future therapeutics designed with a more targeted approach. Detailed in this manuscript is the concept of utilizing peptides possessing an inverse hydropathy to the immunogenic region of proteins to generate anti-idiotypic (anti-Id) and anti-clonotypic T cell receptor (TCR) antibodies (Abs). Theoretically, the anti-Id Abs cross react with Id Abs and negate the powerful machinery of the adaptive immune response with little to no side effects. A series of studies by a number of groups have shown this to be an exciting and intriguing concept that will likely play a role in the future treatment of autoimmune diseases.

RyRCa2+ leak limits cardiac Ca2+ window current overcoming the tonic effect of calmodulinin mice

Ca²⁺ mediates the functional coupling between L-type Ca²⁺ channel (LTCC) and sarcoplasmic reticulum (SR) Ca²⁺ release channel (ryanodine receptor, RyR), participating in key pathophysiological processes. This crosstalk manifests as the orthograde Ca²⁺-induced Ca²⁺-release (CICR) mechanism triggered by Ca²⁺ influx, but also as the retrograde Ca²⁺-dependent inactivation (CDI) of LTCC, which depends on both Ca²⁺ permeating through the LTCC itself and on SR Ca²⁺ release through the RyR. This latter effect has been suggested to rely on local rather than global Ca²⁺ signaling, which might parallel the nanodomain control of CDI carried out through calmodulin (CaM). Analyzing the CICR in catecholaminergic polymorphic ventricular tachycardia (CPVT) mice as a model of RyR-generated Ca²⁺ leak, we evidence here that increased occurrence of the discrete local SR Ca²⁺ releases through the RyRs (Ca²⁺ sparks) causea depolarizing shift in activation and a hyperpolarizing shift inisochronic inactivation of cardiac LTCC current resulting in the reduction of window current. Both increasing fast [Ca²⁺]_i buffer capacity or depleting SR Ca²⁺ store blunted these changes, which could be reproduced in WT cells by RyRCa²⁺ leak induced with Ryanodol and CaM inhibition.Our results unveiled a new paradigm for CaM-dependent effect on LTCC gating and further the nanodomain Ca²⁺ control of LTCC, emphasizing the importance of spatio-temporal relationships between Ca²⁺ signals and CaM function.

Ca(2+) regulation of connexin 43 hemichannels in C6 glioma and glial cells

Connexin hemichannels have a low open probability under normal conditions but open in response to various stimuli, forming a release pathway for small paracrine messengers. We investigated hemichannel-mediated ATP responses triggered by changes of intracellular Ca(2+) ([Ca(2+)](i)) in Cx43 expressing glioma cells and primary glial cells. The involvement of hemichannels was confirmed with gja1 gene-silencing and exclusion of other release mechanisms. Hemichannel responses were triggered when [Ca(2+)](i) was in the 500nM range but the responses disappeared with larger [Ca(2+)](i) transients. Ca(2+)-triggered responses induced by A23187 and glutamate activated a signaling cascade that involved calmodulin (CaM), CaM-dependent kinase II, p38 mitogen activated kinase, phospholipase A2, arachidonic acid (AA), lipoxygenases, cyclo-oxygenases, reactive oxygen species, nitric oxide and depolarization. Hemichannel responses were also triggered by activation of CaM with a Ca(2+)-like peptide or exogenous application of AA, and the cascade was furthermore operational in primary glial cells isolated from rat cortex. In addition, several positive feed-back loops contributed to amplify the responses. We conclude that an elevation of [Ca(2+)](i) triggers hemichannel opening, not by a direct action of Ca(2+) on hemichannels but via multiple intermediate signaling steps that are adjoined by distinct signaling mechanisms activated by high [Ca(2+)](i) and acting to restrain cellular ATP loss.

Ca2+ -calmodulin feedback mediates sensory adaptation and inhibits pheromone-sensitive ion channels in the vomeronasal organ

The mammalian vomeronasal organ (VNO) mediates the regulation of social behaviors by complex chemical signals. These cues trigger transient elevations of intracellular Ca(2+) in vomeronasal sensory neurons (VSNs), but the functional role of such Ca(2+) elevations is unknown. We show that stimulus-induced Ca(2+) entry plays an essential role as a negative feedback regulator of VSN sensitivity. Electrophysiological VSN responses undergo effective sensory adaptation that requires the influx of Ca(2+) and is mediated by calmodulin (CaM). Removal of the Ca(2+)-CaM feedback eliminates this form of adaptation. A key target of this feedback module is the pheromone-sensitive TRPC2-dependent cation channel of VSNs, as its activation is strongly inhibited by Ca(2+)-CaM. Our results reveal a previously unrecognized CaM-signaling pathway that endows the VSNs with a mechanism for adjusting gain and sensitivity of chemosensory signaling in the VNO.

A complementary La/SSB epitope anchored to Sequential Oligopeptide Carrier regulates the anti-La/SSB response in immunized animals

Complementary peptide epitopes, derived from complementary RNA sequences, have been used for suppressing the autoimmune response in experimental autoimmune diseases as myasthenia gravis, allergic neuritis and allergic encephalomyelitis. Aiming at contributing to the development of a tool that could regulate the autoantibody production against La/SSB, which is the main target of autoantibodies in Sjogren's syndrome (SS) and systemic lupus erythematosus (SLE), the complementary epitope, cpep349-364, of the minor T/major B cell epitope of La/SSB, pep349-364, was utilized for the induction of neutralizing anti-cpep349-364 antibodies in rabbit immunizations. Complementary peptides were coupled to an artificial carrier, developed in our laboratory, in order to enhance the complementary potency of cpep349-364 and its counterpart. This carrier, named Sequential Oligopeptide Carrier, SOC(n), formed by the repeating tripeptide Lys-Aib-Gly, adopts helical conformation, which allows the anchored peptide epitopes to preserve their initial reactivity such as molecular recognition, antigenicity/immunogenicity. Our study provides proof of evidence of specific interactions between idiotypic (Id)/anti-idiotypic (anti-Id) antibodies generated in immunized animals by the sense epitope (conjugate I) of La/SSB and its complementary counterpart (conjugate II). It was also demonstrated that the Id/anti-Id association is specifically disrupted by adding either the sense epitope (conjugate I) or its complementary counterpart (conjugate II). A mutual neutralization of Id/anti-Id antibodies was observed in vivo, which implies that generation of anti-Id antibodies by immunization with the complementary La/SSB epitope could scavenge the anti-La/SSB response.

Transient receptor potential channel A1 is directly gated by calcium ions

Members of the superfamily of transient receptor potential (TRP) channels are proposed to play important roles in sensory physiology. As an excitatory ion channel TRPA1 is robustly activated by pungent irritants in mustard and garlic and is suggested to mediate the inflammatory actions of environmental irritants and proalgesic agents. Here, we demonstrate that, in addition to pungent natural compounds, Ca(2+) directly gates heterologously expressed TRPA1 in whole-cell and excised-patch recordings with an apparent EC(50) of 905 nm. Pharmacological experiments and site-directed mutagenesis indicate that the N-terminal EF-hand calcium-binding domain of the channel is involved in Ca(2+)-dependent activation. Furthermore, we determine Ca(2+) as prerequisite for icilin activity on TRPA1.

Possible therapeutic vaccines for canine myasthenia gravis: implications for the human disease and associated fatigue

Myasthenia gravis (MG) is caused by T cell-dependent antibodies reactive with acetylcholine receptors. These autoreactive antibodies cause muscle weakness by interfering with neuromuscular transmission via removal of acetylcholine receptors from the neuromuscular junction as well as changing the architecture of the junction itself. Consequently, muscle fatigue is a debilitating aspect of MG often leading to more general feelings of tiredness not directly due to muscle weakness. We have previously described two peptides that are mimetics of antigen receptors on certain autoreactive T and B cells that are involved in MG. When used as vaccines in the rat model of MG, these peptides prevented and ameliorated disease and muscle fatigue by blunting acetylcholine receptor antibody responses. Such disease protection resulted from vaccine-induced anergizing antibodies against acetylcholine receptor-specific T and B cell antigen receptors. The present study prospectively evaluated the efficacy of these two vaccines in spontaneous acquired MG in pet dogs. When compared to historical controls that were prospectively studied, the vaccines increased the proportion of remitted dogs from 17 to 75%. In comparison to retrospectively studied historical controls that spontaneously remitted from MG, the vaccines accelerated the rate of decline in acetylcholine receptor antibody titers which resulted in a 3-fold decrease in the mean time to remission. These results are suggestive of a new type of targeted therapy that can drive autoimmune responses into long-term remission and possibly afford a means of determining whether correction of a physical cause of muscle weakness also corrects the perception of chronic, generalized fatigue.

Peptide inhibitors of protein kinases-discovery, characterisation and use

Protein kinases are now the second largest group of drug targets, and most protein kinase inhibitors in clinical development are directed towards the ATP-binding site. However, these inhibitors must compete with high intracellular ATP concentrations and they must discriminate between the ATP-binding sites of all protein kinases as well the other proteins that also utilise ATP. It would therefore be beneficial to target sites on protein kinases other than the ATP-binding site. This review describes the discovery, characterisation and use of peptide inhibitors of protein kinases. In many cases, the development of these peptides has resulted from an understanding of the specific protein-binding partners for a particular protein kinase. In addition, novel peptide sequences have been discovered in library screening approaches and have provided new leads in the discovery and/or design of peptide inhibitors of protein kinases. These approaches are therefore providing exciting new opportunities in the development of ATP non-competitive inhibitors of protein kinases.

A complementary peptide approach applied to the design of novel semaphorin/neuropilin antagonists

Semaphorin 3A can inhibit axonal growth and induce neuronal apoptosis following binding to neuropilin-1, with the membrane proximal MAM (meprin, A5, mu) domain in neuropilin-1 playing a key role in the formation of a higher order receptor complex. If functional motifs on semaphorin 3A and/or the MAM domain can be identified, then small-constrained peptides might be developed as antagonists. We have scored peptide pairs for complementary hydropathy and antisense homology to identify a candidate functional motif in the Ig domain of semaphorin 3A, and in the MAM domain of neuropilin-1. Synthetic peptides corresponding to these sequences fully inhibit growth cone collapse induced by semaphorin 3A. A number of smaller peptides derived from the parental sequence also inhibited the response, particularly after they were constrained by a disulfide bond. Finally, we have used an algorithm to design a peptide that is a near-perfect hydropathic complement of the candidate functional site in the MAM domain; this also inhibits the semaphorin 3A response. Thus, an algorithm-driven methodology has led to the identification of three independent semaphorin 3A antagonists. Semaphorin 3F stimulates growth cone collapse following binding to the closest relative to neuropilin-1 in the genome, neuropilin-2. Where tested, the peptides that antagonise semaphorin 3A failed to inhibit the semaphorin 3F response.

Phosphorylated amyloid-beta: the toxic intermediate in alzheimer's disease neurodegeneration

Phosphorylated Amyloid-beta (Abeta) was identified in Alzheimer's disease (AD) brain. Using an anti-sense peptide approach the human cyclin-dependent kinase-1 (CDK-1) was identified as being responsible for Abeta phosphorylation. The phosphorylated Abeta peptide showed increased neurotoxicity and reduced ability to form Congo red-positive fibrils. Mutation of the serine 26 residue and inhibition of Abeta phosphorylation by the CDK-1 inhibitor olomoucine prevented Abeta toxicity, suggesting that the phosphorylated Abeta peptide represents a toxic intermediate. Cannabinoids prevented phosphorylated Abeta toxicity. The results from this study suggest that Abeta phosphorylation could play a role in AD pathology and represent a novel therapeutic target.

Characterization of a peptide inhibitor of Janus kinase 2 that mimics suppressor of cytokine signaling 1 function

Positive and negative regulation of cytokines such as IFN-gamma are key to normal homeostatic function. Negative regulation of IFN-gamma in cells occurs via proteins called suppressors of cytokine signaling (SOCS)1 and -3. SOCS-1 inhibits IFN-gamma function by binding to the autophosphorylation site of the tyrosine kinase Janus kinase (JAK)2. We have developed a short 12-mer peptide, WLVFFVIFYFFR, that binds to the autophosphorylation site of JAK2, resulting in inhibition of its autophosphorylation as well as its phosphorylation of IFN-gamma receptor subunit IFNGR-1. The JAK2 tyrosine kinase inhibitor peptide (Tkip) did not bind to or inhibit tyrosine autophosphorylation of vascular endothelial growth factor receptor or phosphorylation of a substrate peptide by the protooncogene tyrosine kinase c-src. Tkip also inhibited epidermal growth factor receptor autophosphorylation, consistent with the fact that epidermal growth factor receptor is regulated by SOCS-1 and SOCS-3, similar to JAK2. Although Tkip binds to unphosphorylated JAK2 autophosphorylation site peptide, it binds significantly better to tyrosine-1007 phosphorylated JAK2 autophosphorylation site peptide. SOCS-1 only recognizes the JAK2 site in its phosphorylated state. Thus, Tkip recognizes the JAK2 autophosphorylation site similar to SOCS-1, but not precisely the same way. Consistent with inhibition of JAK2, Tkip inhibited the ability of IFN-gamma to induce an antiviral state as well as up-regulate MHC class I molecules on cells at a concentration of approximately 10 microM. This is similar to the K(d) of SOCS-3 for the erythropoietin receptor. These data represent a proof-of-concept demonstration of a peptide mimetic of SOCS-1 that regulates JAK2 tyrosine kinase function.

Ca2+ sensors modulate asthmatic symptoms in an allergic model for asthma

We previously described two novel peptides, Ca2+-like peptide (CALP) 1 and CALP2, which interact with Ca2+-binding EF hand motifs, and therefore have the characteristics to define the role of the Ca2+-sensing regulatory protein calmodulin in asthma. In the present study, the effects of the calcium-like peptides were investigated in an animal model for allergic asthma. For that purpose, sensitized guinea pigs were intratracheally pretreated with CALP1 or CALP2. Thirty minutes later, the animals were challenged with aerosolized ovalbumin. Acute bronchoconstriction was measured as well as characteristic features of asthma 6 and 24 hours (h) after challenge. Neither CALP1 nor CALP2 prevented the anaphylactic response elicited by ovalbumin challenge. However, CALP1 pretreatment attenuated the influx of inflammatory cells in the lungs 6 h after challenge. Furthermore, radical production by these cells was diminished both 6 and 24 h after challenge. Moreover, CALP1 completely inhibited airway hyperresponsiveness in vitro 24 h after challenge. We conclude that CALP1, as a selective calmodulin agonist, inhibits the development of asthmatic features probably via the attenuation of mast cell degranulation and radical production. Specific modulation of calmodulin activity might therefore be a potential new target for the treatment of allergic asthma.

Pharmacological properties of peptides derived from an antibody against the tachykinin NK1 receptor for the neuropeptide substance P

Two peptides were derived from the structural analysis of a previously described monoclonal antibody [Mol. Immunol. 37 (2000) 423] against the tachykinin NK(1) receptor for the neuropeptide substance P. Here we show that these two peptides were able to inhibit the inositol phosphate transduction pathway triggered both by substance P and neurokinin A, another high-affinity endogenous ligand for the tachykinin NK(1) receptor. They also reduced the cAMP production induced by substance P. By contrast, only one antagonist peptide was able to prevent substance P and neurokinin A from binding the receptor, as revealed both by biochemical and autoradiographic studies. First, these results illustrate the generality of the antibody-based strategy for developing new bioactive peptides. Second, they indicate that antagonists, even exhibiting very close amino acid composition, can interact with the tachykinin NK(1) receptor at different contact sites, some of them clearly distinct from the contact domains for endogenous agonists.

Nitric oxide in respiratory diseases

The formation and modulation of nitric oxide (NO) in the lungs is reviewed. Its beneficial and deleterious roles in airways diseases, including asthma, chronic obstructive pulmonary disease, and cystic fibrosis, and in animal models is discussed. The pharmacological effects of agents that modulate NO production or act as NO donors are described. The clinical pharmacology of these agents is described and the therapeutic potential for their use in airways disease is considered.

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.

Cloning, localization, and axonemal function of Tetrahymena centrin

Centrin, an EF hand Ca(2+) binding protein, has been cloned in Tetrahymena thermophila. It is a 167 amino acid protein of 19.4 kDa with a unique N-terminal region, coded by a single gene containing an 85-base pair intron. It has > 80% homology to other centrins and high homology to Tetrahymena EF hand proteins calmodulin, TCBP23, and TCBP25. Specific cellular localizations of the closely related Tetrahymena EF hand proteins are different from centrin. Centrin is localized to basal bodies, cortical fibers in oral apparatus and ciliary rootlets, the apical filament ring and to inner arm (14S) dynein (IAD) along the ciliary axoneme. The function of centrin in Ca(2+) control of IAD activity was explored using in vitro microtubule (MT) motility assays. Ca(2+) or the Ca(2+)-mimicking peptide CALP1, which binds EF hand proteins in the absence of Ca(2+), increased MT sliding velocity. Antibodies to centrin abrogated this increase. This is the first demonstration of a specific centrin function associated with axonemal dynein. It suggests that centrin is a key regulatory protein for Tetrahymena axonemal Ca(2+) responses, including ciliary reversal or chemotaxis.

The anti-adhesive activity of thrombospondin is mediated by the N-terminal domain of cell surface calreticulin

Thrombospondin (TSP) induces reorganization of the actin cytoskeleton and restructuring of focal adhesions through binding of amino acids (aa) 17-35 (hep I peptide) of thrombospondin to a cell surface form of calreticulin (CRT). In this report we provide further evidence for the involvement of calreticulin in thrombospondin signaling and characterize thrombospondin-calreticulin interactions. Wild type but not crt(-/-) cells respond to hep I/TSP. Responsiveness can be restored by incubation of cells with exogenous calreticulin or by transfection with calreticulin. Thrombospondin forms complexes with the CRT-N-domain that are enhanced by physiologic levels of calcium and zinc. Consistent with thrombospondin/CRT-N-domain binding, only the CRT-N-domain blocks hep I- and thrombospondin-stimulated focal adhesion disassembly. A series of glutathione S-transferase-N-domain mutants were used to map the sequence within the N-domain that interacts with TSP/hep I. A construct containing aa 1-43 but not a construct of aa 1-31 supported thrombospondin binding and focal adhesion disassembly. A series of overlapping peptides were used to further map the thrombospondin-binding site. Peptides spanning aa 19-36 (RWIESKHKSDFGKFVLSS) blocked hep I-stimulated focal adhesion disassembly, indicating that the TSP/hep I-binding site is located to this sequence in calreticulin. A mutant fusion protein lacking aa 19-36 (glutathione S-transferase-CRTDeltahep I) failed to restore responsiveness to hep I in crt(-/-) cells, bind thrombospondin, or competitively block focal adhesion disassembly, providing evidence for the role of this calreticulin sequence in mediating thrombospondin signaling.

Ligand-dependent and independent modulation of aryl hydrocarbon receptor localization, degradation, and gene regulation

Changes in the concentration or subcellular location of the key proteins involved in signal transduction pathways have been shown to impact gene regulation. Studies were designed to evaluate the relationship between aryl hydrocarbon receptor (AHR) localization, stability, and gene regulation in a defined system where the endogenous AHR protein could be evaluated. The findings indicate that treatment of cells with geldanamycin (GA) or MG-132 (an inhibitor of the 26S proteasome) results in nuclear translocation of the endogenous AHR in both human HepG2 and murine Hepa-1 cells without induction of endogenous CYP1A1 protein. Exposure to GA resulted in the degradation of AHR by >90% in the nucleus via the 26S proteasome. Importantly, the reduced level of AHR resulted in a 50% reduction in the maximal level of CYP1A1 induced by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). In all treatments the concentration of the AHR nuclear translocator (ARNT) protein was unchanged and had no impact on the localization of the AHR. Thus, ligand-independent translocation of the AHR to the nucleus was not sufficient to induce CYP1A1 in the absence of ligand, but reductions in the level of the endogenous AHR protein pool shifted the dose-response curve for TCDD to the right.

Hydropathic complementarity determines interaction of epitope (869)HITDTNNK(876) in Manduca sexta Bt-R(1) receptor with loop 2 of domain II of Bacillus thuringiensis Cry1A toxins

In susceptible insects, Cry toxin specificity correlates with receptor recognition. In previous work, we characterized an scFv antibody (scFv73) that inhibits binding of Cry1A toxins to cadherin-like receptor. The CDR3 region of scFv73 shared homology with an 8-amino acid epitope ((869)HITDTNNK(876)) of the Manduca sexta cadherin-like receptor Bt-R(1) (Gomez, I., Oltean, D. I., Gill, S. S., Bravo, A., and Soberón, M. (2001) J. Biol. Chem. 276, 28906-28912). In this work, we show that the previous sequence of scFv73 CDR3 region was obtained from the noncoding DNA strand. However, most importantly, both scFv73 CDR3 amino acid sequences of the coding and noncoding DNA strands have similar binding capabilities to Cry1Ab toxin as Bt-R(1) (869)HITDTNNK(876) epitope, as demonstrated by the competition of scFv73 with binding to Cry1Ab with synthetic peptides with amino acid sequences corresponding to these regions. Using synthetic peptides corresponding to three exposed loop regions of domain II of Cry1Aa and Cry1Ab toxins, we found that loop 2 synthetic peptide competed with binding of scFv73 to Cry1A toxins in Western blot experiments. Also, loop 2 mutations that affect toxicity of Cry1Ab toxin are affected in scFv73 binding. Toxin overlay assays of Cry1A toxins to M. sexta brush border membrane proteins showed that loop 2 synthetic peptides competed with binding of Cry1A toxins to cadherin-like Bt-R(1) receptor. These experiments identified loop 2 in domain II of as the cognate binding partner of Bt-R(1) (869)HITDTNNK(876). Finally, 10 amino acids from beta-6-loop 2 region of Cry1Ab toxin ((363)SSTLYRRPFNI(373)) showed hydropathic pattern complementarity to a 10-amino acid region of Bt-R(1) ((865)NITIHITDTNN(875)), suggesting that binding of Cry1A toxins to Bt-R(1) is determined by hydropathic complementarity and that the binding epitope of Bt-R(1) may be larger than the one identified by amino acid sequence similarity to scFv73.

Anti-allergen antibodies can be neutralized by antibodies obtained against a peptide complementary to the allergen: towards a new peptide therapy for allergy

The concept of specific immune treatment against allergic diseases requires the development of antibodies capable of specifically neutralizing anti-allergen antibodies. The aim of the present study was to investigate whether a novel approach, consisting in raising anti-idiotypic blocking antibodies through peptide immunization, could be envisaged in the field of allergy. Using allergy to cow's milk as a model, we prepared polyclonal antibodies against a peptide that is complementary (i.e. hydropathically opposed) to a major epitope of bovine beta-lactoglobulin (BLG), one of the main allergens of bovine milk. Anti-complementary peptide antibodies were found to neutralize in vitro both well-characterized anti-BLG monoclonal antibodies from mice sensitized to BLG and anti-BLG IgE from two patients suffering from milk allergy. These results suggest a new strategy for the functional inhibition of specific disease-associated IgE that may be applicable to the specific treatment of various allergic disorders.

Survey of the year 2000 commercial optical biosensor literature

We have compiled a comprehensive list of the articles published in the year 2000 that describe work employing commercial optical biosensors. Selected reviews of interest for the general biosensor user are highlighted. Emerging applications in areas of drug discovery, clinical support, food and environment monitoring, and cell membrane biology are emphasized. In addition, the experimental design and data processing steps necessary to achieve high-quality biosensor data are described and examples of well-performed kinetic analysis are provided.

Allergen-induced impairment of bronchoprotective nitric oxide synthesis in asthma

BACKGROUND

Endogenous nitric oxide protects against airway hyperresponsiveness (AHR) to bradykinin in mild asthma, whereas AHR to bradykinin is enhanced by inhaled allergens.

OBJECTIVE

Hypothesizing that allergen exposure impairs bronchoprotective nitric oxide within the airways, we studied the effect of the inhaled nitric oxide synthase (NOS) inhibitor N(G)-monomethyl-L-arginine (L-NMMA) on AHR to bradykinin before and after allergen challenge in 10 subjects with atopic asthma.

METHODS

The study consisted of 3 periods (1 diluent and 2 allergen challenges). AHR to bradykinin (PD(20)BK) was examined before and 48 hours after allergen challenge, both after double-blinded pretreatment with L-NMMA or placebo. The accompanying expression of the various NOS isoforms (ecNOS, nNOS, and iNOS) was examined by means of immunohistochemistry in bronchial biopsies obtained after diluent and allergen challenge.

RESULTS

After placebo, AHR to BK worsened after allergen challenge in comparison with before allergen challenge (PD(20)BK, 70.8 nmol [range, 6.3-331] and 257 nmol [35.5-2041], respectively; P =.0004). After L-NMMA, preallergen and postallergen PD(20)BK values (50.1 nmol [1.8-200] vs 52.5 nmol [6.9-204]; P =.88) were similarly reduced (P <.01) and not different from the postplacebo/postallergen value (P >.05). After allergen challenge, the intensity of staining in bronchial epithelium decreased for ecNOS (P =.03) and increased for iNOS (P =.009). These changes in immunostaining were correlated with the accompanying worsening in AHR to BK (R(s) = -0.66 and 0.71; P <.04).

CONCLUSIONS

These data indicate that allergen exposure in asthma induces increased airway hyperresponsiveness to bradykinin through impaired release of bronchoprotective nitric oxide associated with downregulation of ecNOS. This suggests that new therapeutic strategies towards restoring the balance among the NOS isoforms during asthma exacerbations are warranted.

Prevention and reversal of experimental autoimmune myasthenia gravis by a monoclonal antibody against acetylcholine receptor-specific T cells

We have recently described an algorithm to design, among others, peptides with complementarity contour to autoimmune epitopes. Immunization with one such peptide resulted in a monoclonal antibody (mAb), termed CTCR8, that specifically recognized Vbeta15 containing TCR on acetylcholine receptor (AChR) alpha-chain residue 100-116-specific T cells. CTCR8 was found to label the cell surface of AChR100-116-specific T cell lines and clones, immunoprecipitate the TCR from such cells, and block their proliferative responses to AChRalpha100-116. In the present report, we have found that there is a marked reduction in IFN-gamma and no effect on IL-10 production in a CTCR8-treated AChRalpha100-116-specific T cell line. Interestingly, when AChR100-116-primed, primary T cells were stimulated with peptide and treated with CTCR8, there was once again inhibition of IFN-gamma but also marked stimulation of IL-10 production. The change in the Th1/Th2 cytokine profile was paralleled by a reduction in AChR-specific IgG2a and IgM with no effect on IgG1. Remarkably, the most profoundly inhibited Ab population was that which causes experimental autoimmune myasthenia gravis (EAMG) by reaction with the main immunogenic region (alpha61-76) of the AChR. Based on these results, CTCR8 was tested for prophylactic and therapeutic effects in EAMG. EAMG induced by immunization with purified native Torpedo AChR was both inhibited and reversed by CTCR8. These findings suggest a means to produce therapeutic mAb for the treatment of autoimmune diseases.

Attenuation of very late antigen-5-mediated adhesion of bone marrow-derived mast cells to fibronectin by peptides with inverted hydropathy to EF-hands

Release of allergic mediators from mast cells is enhanced by very late Ag (VLA)-5-mediated interaction of these cells with fibronectin. In this report, we show that VLA-5-mediated adhesion of bone marrow-derived mast cells to fibronectin can be induced by two different pathways: first, FcepsilonRI clustering, which depends on calmodulin activation and extracellular Ca(2+), and, second, by Mn(2+) stimulation, which is independent of calmodulin activation and antagonized by Ca(2+). Previous studies have shown the presence of several cation-binding domains in VLA-5 that are homologous to the calcium-binding EF-hands of calmodulin. To show a role for EF-hands of different proteins in VLA-5-mediated adhesion, we used calcium-like peptides (CALP), CALP1 and CALP2, designed to bind to EF-hands based on inverted hydropathy. CALP1 and, more potently, CALP2 inhibited FcepsilonRI-induced adhesion to fibronectin via different mechanisms. The target for the effects of CALP1 and 2 on FcepsilonRI-induced adhesion and degranulation was intracellular and likely involved calmodulin. Interestingly only CALP2 was able to inhibit Mn(2+)-induced calmodulin-independent adhesion by interfering with an extracellular target, which is probably VLA-5. We conclude that CALP1 and 2 can inhibit VLA-5-mediated adhesion of mast cells to fibronectin through binding to EF-hands of multiple proteins, and that these peptides can be used as lead compounds for the development of future therapy against allergy.

Cellular uptake and in situ binding of a peptide agonist for calmodulin

We have used the method of inverted hydropathy to develop peptides that interact with EF hands of calmodulin (CaM). Previously we have shown these peptides specifically interact with their desired target in a productive manner, in that they activated CaM in the absence of Ca(2+). Therefore, we sought to determine whether these peptides would enter cells, remain intact, and interact with CaM in the interior of the cell. Using several techniques we have demonstrated cellular uptake, stability, and an intracellular interaction with CaM with fluorescein-labeled and radiolabeled peptides in Jurkat T cells. The results suggest that these peptides may be useful in the study and the manipulation of Ca(2+)-mediated pathways in cells.

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.