Showing papers by "Torrey Pines Institute for Molecular Studies published in 2000"
TL;DR: The identification of non-acetylated, poly-d-arginine-derived molecules may represent excellent lead compounds for the development of therapeutically useful furin inhibitors, and they are shown to show extended subsite recognition by furin and PC2.
226 citations
TL;DR: Novel approaches to neuroregeneration will, when most effective, make use of the activity-related effects on neurons in the adult brain to activate these stem cells in a targeted manner to enhance brain function.
Abstract: Plasticity is an essential characteristic of the brain: it is part of how the brain functions and is continuous while the brain interacts with the outer world. The state of activation and the level of activity of the entire organism affect the brain's plastic response. Brain plasticity has many substrates, ranging from synapses to neurites and entire cells. The production of new neurons is part of plasticity even in the adult and old brain, but under normal conditions neurogenesis only occurs in two privileged regions of the adult brain: hippocampus and olfactory system. At least in the hippocampus, physical activity stimulates neurogenesis by acting on the proliferation of neuronal stem cells. More specific functions such as learning may be able to recruit new neurons from the pool of cells with neurogenic potential. In a broader context neuronal stem cells can likely be found throughout the brain. Therefore, novel approaches to neuroregeneration will, when most effective, make use of the activity-related effects on neuronal stem cells in the adult brain to activate these stem cells in a targeted manner to enhance brain function.
206 citations
TL;DR: The results indicate that FA solubility plays a major role in governing binding affinities; affinITIES tend to increase with increasing hydrophobicity (decreasing solubilities) of the FA; and thermodynamic parameters are quite different for paralogous but are quite similar for orthologous FABP, suggesting tissue-specific differences in FABPs function that may be conserved across species.
Abstract: Fatty acid binding proteins (FABP) form a family of proteins displaying tissue-specific expression. These proteins are involved in fatty acid (FA) transport and metabolism by mechanisms that also appear to be tissue-specific. Cellular retinoid binding proteins are related proteins with unknown roles in FA transport and metabolism. To better understand the origin of these tissue-specific differences we report new measurements, using the acrylodated intestinal fatty acid binding protein (ADIFAB) method, of the binding of fatty acids (FA) to human fatty acid binding proteins (FABP) from brain, heart, intestine, liver, and myelin. We also measured binding of FA to a retinoic acid (CRABP-I) and a retinol (CRBP-II) binding protein and we have extended to 19 different FA our characterization of the FA-ADIFAB and FA-rat intestinal FABP interactions. These studies extend our previous analyses of human FABP from adipocyte and rat FABPs from heart, intestine, and liver. Binding affinities varied according to the order brain approximately myelin approximately heart > liver > intestine > CRABP > CRBP. In contrast to previous studies, no protein revealed a high degree of selectivity for particular FA. The results indicate that FA solubility (hydrophobicity) plays a major role in governing binding affinities; affinities tend to increase with increasing hydrophobicity (decreasing solubility) of the FA. However, our results also reveal that, with the exception of the intestinal protein, FABPs exhibit an additional attractive interaction for unsaturated FA that partially compensates for their trend toward lower affinities due to their higher aqueous solubilities. Thermodynamic potentials were determined for oleate and arachidonate binding to a subset of the FABP and retinoid binding proteins. FA binding to all FABPs was enthalpically driven. The DeltaH degrees values for paralogous FABPs, proteins from the same species but different tissues, reveal an exceptionally wide range of values, from -22 kcal/mol (myelin) to -7 kcal/mol (adipocyte). For orthologous FABPs from the same tissue but different species, DeltaH degrees values were similar. In contrast to the enthalpic dominance of FA binding to FABP, binding of FA to CRABP-I was entropically driven. This is consistent with the notion that FA specificity for FABP is determined by the enthalpy of binding. Proteins from different tissues also revealed considerable heterogeneity in heat capacity changes upon FA binding, DeltaC(p) values ranged between 0 and -1.3 kcal mol(-1) K(-1). The results demonstrate that thermodynamic parameters are quite different for paralogous but are quite similar for orthologous FABP, suggesting tissue-specific differences in FABP function that may be conserved across species.
161 citations
TL;DR: A mechanism of selective docking of MMP‐2 at tumor cell surfaces, specifically at the sites that include MT1‐MMP and activated integrin αvβ3 is suggested, which may provide a link between spatial regulation of focal proteolysis by the cell surface associated MMPs and the regulation of integrin‐mediated motility of tumor cells.
Abstract: Matrix metalloproteinases (MMPs) and integrins have been implicated in a variety of processes involved in tumor progression. To evaluate the individual roles of integrin alphavbeta3 and membrane-type 1 matrix metalloproteinase (MT1-MMP), as well as the effects of their joint expression on tumor cell functions, MCF7 breast carcinoma cells were transfected stably with either the MT1-MMP, the beta3 integrin subunit or both MT1-MMP and beta3 cDNAs. MT1-MMP expression is accompanied by the functional activation of integrin alphaVbeta3, thereby increasing vitronectin-mediated adhesion and migration of MCF7 cells transfected with MT1-MMP and integrin alphaVbeta3. MT1-MMP-dependent functional activation of alphaVbeta3 correlates with modification(s) of the beta3 subunit, including its higher electrophoretic mobility and affected the LM609-binding site. MCF7 cells jointly expressing MT1-MMP and alphaVbeta3 were the most efficient in adhesion to the recombinant C-terminal domain of MMP-2 as well as in generating soluble and cell surface associated mature MMP-2 enzyme. These findings suggest a mechanism of selective docking of MMP-2 at tumor cell surfaces, specifically at the sites that include MT1-MMP and activated integrin alphaVbeta3. These mechanisms may provide a link between spatial regulation of focal proteolysis by the cell surface associated MMPs and the regulation of integrin-mediated motility of tumor cells.
158 citations
TL;DR: A set of peptide analogues were generated based on the screening of a library built around an existing lytic peptide, and on a deconvolution strategy directed toward activity specificity that served as model systems to further study the effect of biomembrane mimetic systems on the peptides structural behavior relevant to their biological activities.
Abstract: In the race for supremacy, microbes are sprinting ahead. This warning by the World Health Organization clearly demonstrates that the spread of antibiotic-resistant bacteria leads to a global health problem and that antibiotics never seen before by bacteria are urgently needed. Antimicrobial peptides represent such a source for novel antibiotics due to their rapid lytic activity (within minutes) through disruption of cell membranes. However, due to the similarities between bacterial, fungal, and mammalian plasma cell membranes, a large number of antimicrobial peptides have low lytic specificities and exhibit a broad activity spectrum and/or significant toxic effect toward mammalian cells. Mutation strategies have allowed the development of analogues of existing antimicrobial peptides having greater lytic specificities, although such methods are lengthy and would be more efficient if the molecular mechanisms of action of antimicrobial peptides were clearly elucidated. Synthetic combinatorial library approaches have brought a new dimension to the design of novel biologically active compounds. Thus, a set of peptide analogues were generated based on the screening of a library built around an existing lytic peptide, and on a deconvolution strategy directed toward activity specificity. These peptide analogues also served as model systems to further study the effect of biomembrane mimetic systems on the peptides structural behavior relevant to their biological activities.
129 citations
TL;DR: Three‐dimensional cultures of dermal equivalent tissue express angiogenic activity to a greater extent than monolayer cultures, some of which can be assigned to VEGF.
Abstract: Human neonatal fibroblasts were cultured on a lactate-glycollate copolymer scaffold for 12–16 days to form a three-dimensional dermal equivalent tissue. The cellular content of vascular endothelial growth factor (VEGF) mRNA in these three-dimensional cultures was 22-fold greater than that observed in the same fibroblasts grown as monolayers. No induction was shown by hepatocyte growth factor (HGF) or angiopoietin 1 indicating that the effect was specific to VEGF. The predominant VEGF splice variant, detected by RT-PCR corresponded to the 121 amino acid form, with less of the 165 amino acid form. The cell-associated forms (189 and 206 amino acids) comprised less than 1% of the total VEGF mRNA. VEGF and HGF proteins, determined by ELISA, were secreted in physiologically significant amounts, 0.5–4 ng per 24 h/106 cells. Conditioned medium from the three-dimensional cultures stimulated proliferation of endothelial cells in a dose-dependent manner and induced cellular expression of integrin αvβ3. Conditioned medium from the same dermal fibroblasts cultured in monolayer showed little angiogenic activity in any of these assays. Using the chorioallantoic membrane (CAM) angiogenesis assay, the cultures stimulated blood vessel production 2.8-fold over scaffold alone. VEGF-neutralizing antibody reduced the vessel development in the CAM to the level in the scaffold control. Anti-HGF antibody had no significant effect. In conclusion, three-dimensional cultures of dermal equivalent tissue express angiogenic activity to a greater extent than monolayer cultures, some of which can be assigned to VEGF. J. Cell. Physiol. 183:74–82, 2000. © 2000 Wiley-Liss, Inc.
99 citations
TL;DR: Surprisingly, pentapeptides, tetrapeptides and even tripeptides derived from different segments of the optimal ligands were recognized by the autoreactive CD4(+) T cell clones, and some were even more potent than the selecting autoantigen.
Abstract: CD4 T lymphocytes usually recognize peptides of 12–16 amino acids in the context of HLA class II molecules. We have recently used synthetic peptide combinatorial libraries to dissect in detail antigen recognition by autoreactive CD4 T cell clones (TCC). The results of these studies demonstrated that antigen recognition by T cells is highly degenerate and that many cross-reactive ligands can be defined, some of which much more potent than the selecting autoantigen. Based on these observations, we examined the response of a myelin basic protein-specific HLA class II-restricted CD4 TCC to truncation variants of optimal ligands. Surprisingly, pentapeptides, tetrapeptides and even tripeptides derived from different segments of the optimal ligands were recognized by the TCC, and some were even more potent than the selecting autoantigen. In addition, these peptides enhanced the survival of the TCC at low concentration. The relevance of this finding was supported by the generation of pentapeptide-specific CD4 TCC from peripheral blood lymphocytes. These observations not only change existing views on the length requirements for activation of CD4 HLA class II-restricted T cells, but also extend our knowledge about the flexibility of TCR recognition and the potential for cross-reactivity in the immune system.
80 citations
TL;DR: The results suggest that the low level of wild‐type CFTR in the Golgi region reflects a limiting step in selective recruitment by the ER export machinery, an event that is largely deficient in ΔF508.
Abstract: The pathway of transport of the cystic fibrosis transmembrane regulator (CFTR) through the early exocytic pathway has not been examined. In contrast to most membrane proteins that are concentrated during export from the ER and therefore readily detectable at elevated levels in pre-Golgi intermediates and Golgi compartments, wild-type CFTR could not be detected in these compartments using deconvolution immunofluorescence microscopy. To determine the basis for this unusual feature, we analyzed CFTR localization using quantitative immunoelectron microscopy (IEM). We found that wild-type CFTR is present in pre-Golgi compartments and peripheral tubular elements associated with the cis and trans faces of the Golgi stack, albeit at a concentration 2-fold lower than that found in the endoplasmic reticulum (ER). delta F508 CFTR, a mutant form that is not efficiently delivered to the cell surface and the most common mutation in cystic fibrosis, could also be detected at a reduced concentration in pre-Golgi intermediates and peripheral cis Golgi elements, but not in post-Golgi compartments. Our results suggest that the low level of wild-type CFTR in the Golgi region reflects a limiting step in selective recruitment by the ER export machinery, an event that is largely deficient in delta F508. We raise the possibility that novel modes of selective anterograde and retrograde traffic between the ER and the Golgi may serve to regulate CFTR function in the early secretory compartments.
75 citations
TL;DR: The results indicate that a specific MHC molecule not only selects certain peptides, but also is crucial for setting an affinity threshold for TCR recognition, which determines the flexibility in peptide recognition for a given TCR.
Abstract: The TCR recognition of peptides bound to MHC class II molecules is highly flexible in some T cells. Although progress has been made in understanding the interactions within the trimolecular complex, to what extent the individual components and their amino acid composition contribute to ligand recognition by individual T cells is not completely understood. We investigated how single amino acid residues influence Ag recognition of T cells by combining several experimental approaches. We defined TCR motifs for CD4+ T cells using peptide synthetic combinatorial libraries in the positional scanning format (PS-SCL) and single amino acid-modified peptide analogues. The similarity of the TCR motifs defined by both methods and the identification of stimulatory antigenic peptides by the PS-SCL approach argue for a contribution of each amino acid residue to the overall potency of the antigenic peptide ligand. In some instances, however, motifs are formed by adjacent amino acids, and their combined influence is superimposed on the overall contribution of each amino acid within the peptide epitope. In contrast to the flexibility of the TCR to interact with different peptides, recognition was very sensitive toward modifications of the MHC-restriction element. Exchanges of just one amino acid of the MHC molecule drastically reduced the number of peptides recognized. The results indicate that a specific MHC molecule not only selects certain peptides, but also is crucial for setting an affinity threshold for TCR recognition, which determines the flexibility in peptide recognition for a given TCR.
69 citations
TL;DR: The specificity of plasmin is more tightly controlled than previously recognized; interactions with substrates at all subsites between S4 and S2' contribute to catalysis.
64 citations
TL;DR: The use of parallel array synthesis approaches and mixture-based combinatorial libraries for drug discovery is reviewed and indicates a paradigm shift in drug discovery.
Abstract: Technological advances continue to be a central driving force in the acceleration of the drug discovery process. Combinatorial chemistry methods, developed over the past 15 years, represent a paradigm shift in drug discovery. Initially viewed as a curiosity by the pharmaceutical industry, combinatorial chemistry is now recognized as an essential tool that decreases the time of discovery and increases the throughput of chemical screening by as much as 1000-fold. The use of parallel array synthesis approaches and mixture-based combinatorial libraries for drug discovery is reviewed.
TL;DR: 3D structures of the A.aeolicus protein and its Escherichia coli homolog are reported, consistent with a proposed model for asymmetrical docking of the convex side of tRNA to the dimer.
Abstract: Trbp111 is a 111 amino acid Aquifex aeolicus structure-specific tRNA-binding protein that has homologous counterparts distributed throughout evolution. A dimer is the functional unit for binding a single tRNA. Here we report the 3D structures of the A.aeolicus protein and its Escherichia coli homolog at resolutions of 2.50 and 1.87 A, respectively. The structure shows a symmetrical dimer of two core domains and a central dimerization domain where the N- and C-terminal regions of Trbp111 form an extensive dimer interface. The core of the monomer is a classical oligonucleotide/oligosaccharide-binding (OB) fold with a five-stranded ss-barrel and a small capping helix. This structure is similar to that seen in the anticodon-binding domain of three class II tRNA synthetases and several other proteins. Mutational analysis identified sites important for interactions with tRNA. These residues line the inner surfaces of two clefts formed between the ss-barrel of each monomer and the dimer interface. The results are consistent with a proposed model for asymmetrical docking of the convex side of tRNA to the dimer.
TL;DR: A lipid phase mediated process is consistent with results for the transport of fatty acids across erythrocytes but provides a less adequate explanation for fatty acid transport across more complex cells.
Abstract: The mechanism by which fatty acids are transported across cell membranes is controversial. The essence of the controversy is whether transport requires membrane protein mediation or whether the membrane's lipid phase provides a pathway so rapid that a protein is not needed. This review focuses on the mechanisms of fatty acid transport across lipid bilayer membranes. These results for lipid membranes are used to help evaluate transport across cell membranes. Within the context of this analysis, a lipid phase mediated process is consistent with results for the transport of fatty acids across erythrocytes but provides a less adequate explanation for fatty acid transport across more complex cells.
TL;DR: Results indicate that residues KYNFSF form a novel, distal binding site for the CP, but not CVF convertase, which is found in diverse proteins including netrins and tissue inhibitors of metalloproteinases.
Abstract: Previous studies focused on indels in the complement C345 protein family identified a number of potential protein-protein interaction sites in components C3 and C5. Here, one of these sites in C5, near the alpha-chain C terminus, was examined by alanine-scanning mutagenesis at 16 of the 18 non-alanine residues in the sequence KEALQIKYNFSF RYIYPLD. Alanine substitutions affected activities in the highly variable manner characteristic of binding sites. Substitutions at the lysine or either phenylalanine residue in the central KYNFSF sequence had the greatest effects, yielding mutants with <20% of the normal activity. These three mutants were also resistant to the classical pathway (CP) C5 convertase, with sensitivities roughly proportional to their hemolytic activities, but had normal susceptibilities to the cobra venom factor (CVF)-dependent convertase. Synthetic peptide MGKEALQIKYNFS-NH2 was found similarly to inhibit CP but not CVF convertase activation, and the effects of alanine substitutions in this peptide largely reflected those of the equivalent mutations in C5. These results indicate that residues KYNFSF form a novel, distal binding site for the CP, but not CVF convertase. This site lies approximately 880 residues downstream of the convertase cleavage site within a module that has been independently named C345C and NTR; this module is found in diverse proteins including netrins and tissue inhibitors of metalloproteinases.
TL;DR: The deconvolution of hexapeptide libraries based both on inhibition of an enzymatic reaction as well as on accumulation of reaction intermediates is a novel approach to finding useful tools for dissecting a biochemical pathway.
TL;DR: Linkage disequilibrium analyses showed that the val50ile and gln576arg variants are in complete equilibrium with each other, although they are separated by only about 21 kilobases of genomic DNA, suggesting that a very dense SNP map may be required to exclude or detect disease associations with some candidate genes.
Abstract: Genetic linkage analysis in families with multiple cases of inflammatory bowel disease (IBD) has mapped a gene which confers susceptibility to IBD to the pericentromeric region of chromosome 16 (IBD1). The linked region includes the interleukin(IL)-4 receptor gene (IL4R). Since IL-4 regulation and expression are abnormal in IBD, the IL4R gene is thus both a positional and functional candidate for IBD1. We screened the gene for single-nucleotide polymorphisms (SNPs) by fluorescent chemical cleavage analysis, and tested a subset of known and novel SNPs for allelic association with IBD in 355 families, which included 435 cases of Crohn's disease and 329 cases of ulcerative colitis. No association was observed between a haplotype of four SNPs (val50ile, gln576arg, A3044G, G3289A) and either the Crohn's disease or ulcerative colitis phenotypes using the transmission disequilibrium test. There was also no evidence for association when the four markers were analyzed individually. The results indicate that these variants are not significant genetic determinants of IBD, and that the IL4R gene is unlikely to be IBD1. Linkage disequilibrium analyses showed that the val50ile and gln576arg variants are in complete equilibrium with each other, although they are separated by only about 21 kilobases of genomic DNA. This suggests that a very dense SNP map may be required to exclude or detect disease associations with some candidate genes.
TL;DR: A mixture-based synthetic combinatorial library composed of 23 375 imidazopyridoindoles inhibited both Abeta25-35 and Abeta1-42 neurotoxicity in the low- to mid-micromolar range, supporting the relationship between inhibition of the Abeta aggregation process and neurotoxicity.
TL;DR: Mixture-based library approaches for drug discovery and vaccine development will be reviewed, and the use of mixture-based synthetic combinatorial libraries was one of the first approaches presented.
Patent•
21 Apr 2000TL;DR: The synthesis of di-and tri-substituted 1,4-diazacyclic compounds with one ring carbonyl group and 6-8 atoms in the cyclic ring is discussed in this article.
Abstract: The synthesis of individual di- and tri-substituted-1,4-diazacyclic compounds having 6- to 8-atoms in the cyclic ring, their corresponding 1,6-diketo-2,5-diazacyclic compounds and similar 1,4-diazacyclic ring compounds having one ring carbonyl group and 6-8 atoms in the ring is disclosed, as are libraries of such compounds. Methods of preparing and using the libraries of compounds as well as individual compounds of the libraries are also disclosed.
TL;DR: An efficient method for the solid phase synthesis of 1,6-disubstituted 2,3-diketopiperazine and 1,4,5-trisubstitute 2, 3-diphenazine derivatives is described, an example of a broader approach to the solidphase synthesis of individual heterocyclic compounds using peptides directly or indirectly as starting materials.
TL;DR: An averages-based method of short term postmortem interval estimation was compared to eight other methods, and found to predict post autopsy interval considerably more accurately, and for much longer periods of time.
TL;DR: The events that regulate trophoblast invasion need to be characterized at the transcriptional level, and large-scale gene expression profiling of trophoblasts of distinct invasive stages could be carried out on fixed tissue obtained by laser-directed microdissection.
TL;DR: In this article, an efficient solid-phase synthesis method was described for branched thiohydantoin benzimidazolinethiones and triconoxalinediones using 4-fluoro-3-nitrobenzoic acid.
TL;DR: In an attempt to explain binding disparities, it is determined that Orphanin/Nociceptin binds to glass fiber filtermats in a "specific" manner; these new data are presented.
TL;DR: Results indicate the importance of the C-terminal region of the 42-kDa of binary toxin, in general, and particularly the residue (312)R for biological activity against mosquito larvae.
TL;DR: By time–resolved fluorescence change experiments that folding of LZ16A to D and T can be described, it is shown that the designed 29–residue peptide LZ 16A was shown previously to be in a concen–tration–dependent equilibrium between unfolded monomer, folded dimer, and folded trimer.
Abstract: Coiled coils consist of two or more amphipathic a-helices wrapped around each other to form a superhelical structure stabilized at the interhelical interface by hydrophobic residues spaced in a repeating 3-4 sequence pattern. Dimeric coiled coils have been shown to often form in a single step reaction in which association and folding of peptide chains are tightly coupled. Here, we ask whether such a simple folding mechanism may also apply to the formation of a three-stranded coiled coil. The designed 29-residue peptide LZ16A was shown previously to be in a concentration-dependent equilibrium between unfolded monomer (M), folded dimer (D), and folded trimer (T). We show by time-resolved fluorescence change experiments that folding of LZ16A to D and T can be described by 2M (k1) (k(-1)) D and M + D (k2) (k(-2)) T. The following rate constants were determined (25 degrees C, pH 7): k1 = 7.8 x 10(4) M(-1) s(-1), k(-1) = 0.015 s(-1), k2 = 6.5 x 10(5) M(-1) s(-1), and k(-2) = 1.1 s(-1). In a separate experiment, equilibrium binding constants were determined from the change with concentration of the far-ultraviolet circular dichroism spectrum of LZ16A and were in good agreement with the kinetic rate constants according to K(D) = k1/2k(-1) and K(T) = k2/k(-2). Furthermore, pulsed hydrogen-exchange experiments indicated that only unfolded M and folded D and T were significantly populated during folding. The results are compatible with a two-step reaction in which a subpopulation of association competent (e.g., partly helical) monomers associate to dimeric and trimeric coiled coils.
TL;DR: Both pharmacokinetic and pharmacodynamic factors may contribute to the modest cumulative toxicity observed with AG2034, and the recommended phase II dose is 5.0 mg/m2.
Abstract: Purpose: To identify a recommended phase II dose for the second generation glycinamide ribonucleotide transformylase (GARFT) inhibitor, AG2034, administered by intravenous bolus every 3 weeks without folate supplementation and to describe AG2034 pharmacokinetics. Methods: Adults with advanced malignancies were enrolled in cohorts of three per dose level with expansion to six upon observation of dose-limiting toxicity (DLT). The maximum tolerated dose (MTD) was defined as the dose at which two of up to six patients experienced DLT. Upon identification of an MTD and evidence of cumulative toxicity, a lower intermediate dose was explored as a candidate phase II dose. AG2034 plasma concentrations were measured using an ELISA assay. Results and conclusions: The recommended phase II dose is 5.0 mg/m2. DLTs were anemia, thrombocytopenia, mucositis, diarrhea, hyperbilirubinemia, fatigue, and insomnia. Toxicities were modestly cumulative over three courses. Pharmacokinetic analysis showed a dose-AUC0–24 relationship and a progressive increase in AG2034 AUC0–24 over three courses. Both pharmacokinetic and pharmacodynamic factors may contribute to the modest cumulative toxicity observed with AG2034.
TL;DR: In this paper, an efficient method for the solid phase synthesis of mono-, di-and triureas from resin-bound monoamines, diamines and triamines is described. But this method is not suitable for the synthesis of amides.
TL;DR: The exhaustive reduction of resin-bound tripeptides with borane afforded three secondary amines and one primary amine, and the corresponding bis-cyclic thiourea in good purity and yield.
TL;DR: The present peptides are the shortest peptide calmodulin antagonists reported to date showing potential in vivo activity and appear to adopt a partial helical conformation similar to other known cal modulin-binding peptides.
Abstract: Calmodulin is known to bind to various amphipathic helical peptide sequences, and the calmodulin–peptide binding surface has been shown to be remarkably tolerant sterically. d-Amino acid peptides, therefore, represent potential non-hydrolysable intracellular antagonists of calmodulin. In the present study, synthetic combinatorial libraries have been used to develop novel d-amino acid hexapeptide antagonists to calmodulin-regulated phosphodiesterase activity. Five hexapeptides were identified from a library containing over 52 million sequences. These peptides inhibited cell proliferation both in cell culture using normal rat kidney cells and by injection via the femoral vein following partial hepatectomy of rat liver cells. These hexapeptides showed no toxic effect on the cells. Despite their short length, the identified hexapeptides appear to adopt a partial helical conformation similar to other known calmodulin-binding peptides, as shown by CD spectroscopy in the presence of calmodulin and NMR spectroscopy in DMSO. The present peptides are the shortest peptide calmodulin antagonists reported to date showing potential in vivo activity.