Fluoroaluminate stimulates phosphorylation of p130 Cas and Fak and increases attachment and spreading of preosteoblastic MC3T3-E1 cells.

Fluoroaluminate is a G-protein activator, it stimulates osteoblastic cells in culture, and is a bone-forming agent in vivo. To elucidate the mechanisms of G-protein-mediated action of fluoroaluminate in osteoblasts, we studied protein tyrosine phosphorylation in the preosteoblastic cell line MC3T3-E1. Fluoroaluminate, lysophosphatidic acid (LPA; an agonist for G-protein-coupled receptor), or adhesion to type I collagen all stimulated phosphorylation of a similar set of proteins, including p130, p120, p110 (previously identified as proline-rich tyrosine kinase 2, Pyk2), and p70. The phosphorylation of these proteins was sensitive to an Src inhibitor, but not to a Gi-protein inactivator, pertussis toxin. By purification/mass spectrometry and by immunodepletion, p130 protein was identified as p130 Cas (Crk-associated protein), a Src substrate and a protein involved in signaling by cell-adhesion receptors, integrins. Phosphorylation of immunoprecipitated p130 Cas increased upon stimulation with fluoroaluminate and with agonists of G-protein-coupled receptors, but not with growth factors. By immunodepletion, the p120 protein was identified as focal adhesion kinase, Fak. The addition of fluoroaluminate during cell attachment to type I collagen further stimulated phosphorylation of p130 Cas and of Fak. Simultaneously, fluoroaluminate increased the number of attached MC3T3-E1 cells and their spreading. These novel aspects of fluoroaluminate action in cell culture may be important for the bone-forming action of fluoroaluminate in vivo.

Phosphorylation disrupts the central helix in Op18/stathmin and suppresses binding to tubulin.

Protein phosphorylation represents a ubiquitous control mechanism in living cells. The structural prerequisites and consequences of this important post-translational modification, however, are poorly understood. Oncoprotein 18/stathmin (Op18) is a globally disordered phosphoprotein that is involved in the regulation of the microtubule (MT) filament system. Here we document that phosphorylation of Ser63, which is located within a helix initiation site in Op18, disrupts the transiently formed amphipathic helix. The phosphoryl group reduces tubulin binding 10-fold and suppresses the MT polymerization inhibition activity of Op18's C-terminal domain. Op18 represents an example where phosphorylation occurs within a regular secondary structural element. Together, our findings have implications for the prediction of phosphorylation sites and give insights into the molecular behavior of a globally disordered protein.

Towards high performance two-dimensional gel electrophoresis using ultrazoom gels.

Proteomics is the analysis of protein expression in cells or tissues, e.g., to study cellular processes at the molecular level. Ultimately, a proteome analysis should encompass most if not all protein species in a biological sample, including those present in low copy numbers. We are developing two-dimensional gel electrophoresis technology by applying narrow pH range ultrazoom gels to enhance resolution and to improve the detection of low abundance proteins. Ultrazoom gels in the acidic pH range allow the detection of proteins down to 300 copies per cell of a B-lymphoma cell line. Protein separation in the alkaline pH range, however, still requires optimization, especially in conjunction with high sample loads.

Op18/stathmin caps a kinked protofilament-like tubulin tetramer.

Oncoprotein 18/stathmin (Op18), a regulator of microtubule dynamics, was recombinantly expressed and its structure and function analysed. We report that Op18 by itself can fold into a flexible and extended alpha-helix, which is in equilibrium with a less ordered structure. In complex with tubulin, however, all except the last seven C-terminal residues of Op18 are tightly bound to tubulin. Digital image analysis of Op18:tubulin electron micrographs revealed that the complex consists of two longitudinally aligned alpha/beta-tubulin heterodimers. The appearance of the complex was that of a kinked protofilament-like structure with a flat and a ribbed side. Deletion mapping of Op18 further demonstrated that (i) the function of the N-terminal part of the molecule is to 'cap' tubulin subunits to ensure the specificity of the complex and (ii) the complete C-terminal alpha-helical domain of Op18 is necessary and sufficient for stable Op18:tubulin complex formation. Together, our results suggest that besides sequestering tubulin, the structural features of Op18 enable the protein specifically to recognize microtubule ends to trigger catastrophes.

Mass spectrometric characterization of stathmin isoforms separated by 2D PAGE.

In proteome analysis, the determination of the phosphorylation status of proteins and protein isoforms, which have been separated by two-dimensional polyacrylamide gel electrophoresis (2D PAGE), is of prime importance in addition to their identification. In this study, the extent to which such information can be directly extracted from the mass spectrometric data used for identification was evaluated. By searching for metastable peaks which are characteristic for loss of phosphoric acid, the Ser-phosphorylated peptides were identified with a high success rate in reflector matrix-assisted laser desorption/ionization (MALDI) mass maps of in-gel digested proteins. Furthermore, by employing a double enzymatic strategy using trypsin and Glu-C in parallel, improved sequence coverage and additional separation of the potential phosphorylation sites of the isoforms were achieved. The precise location of the modified sites within an identified phosphopeptide was obtained by submitting the corresponding molecular ions directly to nano-electrospray tandem mass spectrometric analysis. In this way the detailed phosphorylation status of six isomers of stathmin separated by 2D PAGE was determined. Two of these six isomers were phosphorylated at all four known sites (serines 15, 24, 37 and 62) and were probably derived from the previously reported alpha and beta forms, which differ by a yet unknown modification. In addition, isomers phosphorylated at serines 15, 24 and 37, serines 24, 37 and 62, serines 24 and 37 and serine 37 only were characterized.

Identification of Man alpha1-3Man alpha1-2Man and Man-linked phosphate on O-mannosylated recombinant leech-derived tryptase inhibitor produced by Saccharomyces cerevisiae and determination of the solution conformation of the mannosylated polypeptide.

The production of recombinant leech-derived tryptase inhibitor (rLDTI) by two different strains of Saccharomyces cerevisiae resulted in the secretion of non-glycosylated and glycosylated rLTDI. Monosaccharide analysis and a-mannosidase treatment demonstrated that glycosylated rLDTI was exclusively alpha-mannosylated. A trypsin digest of reduced and S-carboxymethylated glycosylated rLDTI was separated on a reverse-phase HPLC column. Glycopeptides identified by a combination of matrix-assisted laser desorption mass spectrometry, amino acid sequence analysis, and monosaccharide analysis revealed the presence of different glycoforms. It was found that Ser24, Ser33 and Ser36 were partially glycosylated with a single mannose residue, whereas Thr42 in glycosylated rLDTI from both strains was fully occupied with manno-oligosaccharides with a degree of polymerization ranging over 1-3 and 1-13 depending on the yeast strain. In phosphorylated rLDTI a single phosphate group was predominantly located at the innermost Man residue of units of mannobiose, mannotriose, mannotetraose and mannopentaose at Thr42. Oligosaccharides released by alkaline treatment were reduced by sodium borohydride and separated by high-pH anion-exchange chromatography on a CarboPac MA1 column, and analyzed by one- and two-dimensional 1H-NMR spectroscopy. Besides the major oligosaccharide Man alpha1-2Man-ol, the (for yeast protein O-glycosylation) unusual Man alpha1-3Man alpha1-2Man-ol was determined. The solution conformation of glycosylated rLDTI was investigated by two-dimensional NMR spectroscopy. Structure calculations by means of distance geometry showed that glycosylated rLDTI is compactly folded and contained small secondary structure elements. Analysis of the chemical shifts showed that amino acids Val32-Ser33, Ser36-Ser39 and Thr42 were affected by the O-mannosylation. In addition, changes in chemical shift were observed within the beta-hairpin peptide regions Val13-Ser16 and Gly18-Tyr21 attributed to direct interactions of the mannose residue at Ser36. Furthermore, the protein-linked oligosaccharides were spatially grouped in a position opposite of the canonical binding loop.

Unique chemical reactivity of His-21 of CRM-197, a mutated diphtheria toxin.

CRM-197 is a mutated diphtheria toxin (63000 Da) widely used as a carrier protein of conjugated vaccines. Among the 14 histidines of CRM-197, His-21 was found to be modified selectively with iodoacetamide based reagents. This finding suggests a simplified method for the preparation of conjugate vaccines crosslinked to CRM-197. A bifunctional iodoacetamide, N,N'-(2-hydroxy-1,3-propanediyl)-bis-12-iodoacetamidel (I-CH2-CONH-CH2-CH(OH)-CH2-NHCO-CH2-I) (HPBIA), was synthesized and allowed to react with CRM-197. In the alkaline buffer of pH 8.0-8.4, HPBIA was shown to react and intra-bridge His-21 and Lys-24 of CRM-197 sequentially. At lower pH (7.1-7.5) in the phosphate buffer, the reactivity of Lys-24 toward HPBIA was suppressed drastically. Under these conditions, His-21 could be specifically labeled with HPBIA. Initial experiments have demonstrated that HPBIA modified CRM-197 is able to crosslink to a cysteine-containing peptide. These results offer a potential route for improving the homogeneity of CRM-197 based protein-peptide as well as protein-polysaccharide conjugates.

Novel C5a receptor antagonists regulate neutrophil functions in vitro and in vivo.

Novel recombinant human C5a receptor antagonists were discovered through modification of the C terminus of C5a. The C5a1-71T1M,C27S,Q71C monomer, (C5aRAM; CGS 27913), was a pure and potent functional antagonist. The importance of a C-terminal cysteine at position 71 to antagonist properties of C5aRAM was confirmed by studying C5a1-71 derivatives with replacements of Q71, C5a derivatives of various lengths (70-74) with C-terminal cysteines, and C5a derivatives of various lengths (71-74) with Q71C replacements. The majority of C5a1-71Q71 derivatives were agonists (C5a-like) in the human neutrophil C5a-induced intracellular calcium mobilization assay. The C5a1-71Q71C derivative was an antagonist. C5a derivatives of lengths 73 and 74 with C-terminal cysteines were agonists, while lengths 70 to 72 were antagonists. C5a derivatives of lengths 72, 73, and 74 with Q71C replacements were agonists, while, again, C5a1-71Q71C was an antagonist. C5aRAM and its adducts, including its dimer, C5aRAD (CGS 32359), were pure antagonists. Additionally, CSaRAM and CSaRAD inhibited binding of 125I-labeled recombinant human C5a to neutrophil membranes (Ki = 79 and 2 pM, respectively), C5a-stimulated neutrophil intracellular calcium mobilization (8 and 13 nM), CD11b integrin up-regulation (10 and 1 nM), superoxide generation (182 and 282 nM), lysozyme release (1 and 2 microM), and chemotaxis (11 and 7 microM). In vivo, intradermal injection of C5aRAM inhibited C5a-induced dermal edema in rabbits. Furthermore, a 5-mg/kg i.v. bolus of C5aRAD significantly inhibited C5a-induced neutropenia in micropigs when challenged with C5a 30 min after C5aRAD administration. C5aRAM and C5aRAD are novel, potent C5a receptor antagonists devoid of agonist or proinflammatory activity with demonstrated efficacy in vitro and in vivo.

Glyceraldehyde-3-phosphate dehydrogenase, the putative target of the antiapoptotic compounds CGP 3466 and R-(-)-deprenyl.

R-(-)-Deprenyl (Selegiline) represents one of the drugs currently used for the treatment of Parkinson's disease. This compound was shown to protect neurons or glias from programmed cell death in a variety of models. The mechanism of action of neuroprotection as well as inhibition of apoptosis remains elusive. CGP 3466 is a structurally related analog of R-(-)-deprenyl that exhibits virtually no monoamine oxidase type B inhibiting activity but is neuroprotective in the picomolar concentration range. We showed specific binding of CGP 3466 to glyceraldehyde-3-phosphate dehydrogenase by affinity binding, by affinity labeling, and by means of BIAcore(R) technology. Apoptosis assays based on the human neuroblastoma cell line PAJU established the importance of this interaction for mediating drug-induced inhibition of programmed cell death.

Neoepitope immunoassay: an assay for human interleukin 1 beta based on an antibody induced conformational change.

A secondary monoclonal antibody (mAb2) was generated by immunization with immune complexes of human IL-1 beta and a primary monoclonal (mAb1). mAb2 bound to a neoepitope on the IL-1 beta/mAb1-complex with a dissociation constant (Kd) of 26 pM but not to uncomplexed IL-1 beta. As assessed by the binding of labeled IL-1 beta and neutralization of bioactivity, mAb2 enhanced the affinity of IL-1 beta to mAb1; Kd-values were 108 pM in absence and 5.4 pM in presence of mAb2. By analyzing a series of mutants of IL-1 where surface loops had been exchanged with the corresponding loops of human IL-1 receptor antagonist protein, a critical region responsible for mAb2 binding was localized to the C-terminal region. In addition to mAb1/IL-1 beta-complexes, mAb2 bound pro-IL-1 beta/mAb1 complexes as well as pro-IL-1 beta suggesting that mAb2 recognized a conformation of IL-1 beta resembling that of pro-IL-1 beta. Using this pair of mAbs, chemiluminescent and enzyme linked assays with detection limits of 2 pg/ml hIL-1 beta have been established.

Variation in N-linked carbohydrate chains in different batches of two chimeric monoclonal IgG1 antibodies produced by different murine SP2/0 transfectoma cell subclones.

Two chimeric human/murine monoclonal antibodies were constructed by substitution of the murine constant regions with human gamma 1 and kappa constant regions for heavy and light chains, respectively. The chimeric human/murine molecules are anti-idiotypic antibodies, meaning that they were directed against the antigen binding site in the variable region of another antibody. Antibody batches were produced under identical production conditions, using two selected SP2/0 myeloma cell subclones, which produce chimeric antibodies with different variable regions, but identical constant regions. Several samples were collected during the production of the antibodies in hollow-fibre reactors. The heavy chain, but not the light chain, of the two different chimeric IgG1 antibodies is glycosylated. Structural analysis of the enzymically released N-linked carbohydrate chains by 1H-NMR spectroscopy, as well as by chromatographic profiling, demonstrated that the collection of N-glycans comprises a small amount of monoantennary, and for the greater part diantennary structures. The N-glycans are completely (alpha 1-->6)-fucosylated at the innermost GlcNAc residue. The antennae of the neutral diantennary N-glycans are built up from GlcNAc beta 1-->2, Gal beta 1-->4GlcNAc beta 1-->2 or Gal alpha 1-->3G alpha 1 beta 1-->4GlcNAc beta 1-->2 elements, whereas the antennae of the neutral monoantennary carbohydrate chains have only (beta 1-->2)-linked GlcNAc residues. Galactosylation of the GlcNAc beta 1-->2Man alpha 1-->6 branch occurs four times more frequently than that of the GlcNAc beta 1-->2Man alpha 1-->3 branch, independently of the production batch. A small amount of the diantennary N-glycans are mono- or disialylated, carrying N-acetylneuraminic acid (Neu5Ac) or N-glycolylneuraminic acid (Neu5Gc), exclusively (alpha 2-->6)-linked to beta Gal. Analysis of the different production batches demonstrates that the structures of the N-linked carbohydrate chains are identical in the two chimeric antibodies, but that the relative amounts of the major oligosaccharide components, the degree of sialylation and the molar ratio of Neu5Ac to Neu5Gc varies with the SP2/0 cell subclone, and only slightly with cell age.

The major N-linked carbohydrate chains from human urokinase. The occurrence of 4-O-sulfated, (alpha 2-6)-sialylated or (alpha 1-3)-fucosylated N-acetylgalactosamine(beta 1-4)-N-acetylglucosamine elements.

The primary structure of the major N-linked carbohydrate chains attached to Asn302 of urinary-type plasminogen activator (urokinase) have been determined. Urokinase was completely deglycosylated with peptide-N4-(N-acetyl-beta-glucosaminyl)asparagine amidase F from Flavobacterium meningosepticum. Released oligosaccharides were separated from the remaining protein using gel-permeation chromatography on Bio-Gel P-100, and then on Bio-Gel P-6. Fractionation of the oligosaccharides was achieved by a combination of FPLC anion-exchange chromatography on Mono Q HR 5/5 and amine-adsorption HPLC on LiChrospher 100-NH2. Analysis by 1H-NMR spectroscopy demonstrated that the collection of N-glycans comprises di-, tri-, and tri'-antennary structures. The glycans contain predominantly GalNAc beta 1-4GlcNAc beta instead of Gal beta 1-4GlcNAc beta elements. The GalNAc residue is mainly sulfated at O4, or to a lesser extent it bears N-acetylneuraminic acid at O6; alternatively the GlcNAc residue can be fucosylated at O3. The major component, which accounts for more than 30 mol/100 mol of the total oligosaccharide pool, consists of an (alpha 1-6)-fucosylated diantennary N-linked carbohydrate chain with (SO4-)-4GalNAc beta 1-4GlcNAc beta 1-2 antennae.

Characterization and direct glycoform profiling of a hybrid plasminogen activator by matrix-assisted laser desorption and electrospray mass spectrometry: correlation with high-performance liquid chromatographic and nuclear magnetic resonance analyses of the released glycans.

Mass spectrometric analysis of the recombinant hybrid plasminogen activator K2tu-PA at the native glycoprotein and corresponding protein level (high mass) is described. For gross structural characterization of the major glycotypes present, a combination of enzymatic degradation and matrix-assisted laser desorption mass spectrometric analysis of the products proved convenient. In this way, mono- and di-N-glycosylated one- and two-chain molecules, unresolved in the spectra of native material, were identified, with the one-chain type monoglycosylated at Asn247 representing the major component. Actual detection of resolved original glycoforms, or unresolved groups thereof when composed of isobaric species, and their assignments regarding antennicity and degree of sialylation were possible by electrospray mass spectrometry for the major monoglycosylated one-chain species. Desialation also allowed detection of the diglycosylated one-chain species as a minor constituent. The electrospray mass spectrometric results were correlated with structural and quantitative data available from a parallel high-performance liquid chromatographic and 1H nuclear magnetic resonance study performed at the glycan (low mass) level on liberated individual carbohydrate components. The results of the two studies showed full consistency in all respects amenable to evaluation, i.e. excellent agreement for the assignments of antennicity and degree of sialylation of the major glycan components, and good agreement for the determination of proportions in which these were present in the major monoglycosylated glycoprotein. This provided a sound basis for direct glycoform profiling by electrospray mass spectrometry. Typical applications to batch quality control and to structural characterization of non-standard material are shown.

A mutational analysis of receptor binding sites of interleukin-1 beta: differences in binding of human interleukin-1 beta muteins to human and mouse receptors.

The 3-D crystal structure of interleukin-1 beta (IL-1 beta) has been used to define its receptor binding surface by mutational analysis. The surface of IL-1 beta was probed by site-directed mutagenesis. A total of 27 different IL-1 beta muteins were constructed, purified and analyzed. Receptor binding measurements on mouse and human cell lines were performed to identify receptor affinities. IL-1 beta muteins with modified receptor affinity were evaluated for structural integrity by CD spectroscopy or X-ray crystallography. Changes in six surface loops, as well as in the C- and N-termini, yielded muteins with lower binding affinities. Two muteins with intact binding affinities showed 10- to 100-fold reduced biological activity. The surface region involved in receptor binding constitutes a discontinuous area of approximately 1000 A2 formed by discontinuous polypeptide chain stretches. Based on these results, a subdivision into two distinct local areas is proposed. Differences in receptor binding affinities for human and mouse receptors have been observed for some muteins, but not for wild-type IL-1 beta. This is the first time a difference in binding affinity of IL-1 beta muteins to human and mouse receptors has been demonstrated.

Monoclonal antibody based enzyme-linked and chemiluminescent assays for the human interleukin-1 receptor antagonist. Application to measure hIL-1ra levels in monocyte cultures and synovial fluids.

Interleukin-1 receptor antagonist (IL-1ra) has the potential to counteract at least part of the biological effects of interleukin-1. The outcome of an inflammatory reaction may therefore be determined by the balance between IL-1 and IL-1ra, rather than by IL-1 alone. We have developed an immunoassay to address this issue as well as to assess the effects of anti-inflammatory agents on the expression of IL-1 and IL-1ra in vitro or in body fluids. Recombinant human IL-1ra was expressed in an E. coli system, purified to homogeneity, and used to derive monoclonal antibodies in mice as well as polyclonal antibodies in rabbits. A sandwich ELISA was constructed with F(ab')2 fragments of a high affinity monoclonal antibody and the rabbit serum as a source of secondary antibody. The assay required no sample treatment to avoid interference by rheumatoid factor. The measuring range was 0.020-2 ng/ml. By labelling a second monoclonal antibody with an acridinium ester, a chemiluminescence assay with a wider measuring range (0.050-15 ng/ml) was generated. In accord with published data, we found that IL-1ra was secreted by human monocytes stimulated with LPS, Zymosan, IL-1 alpha, or human IgG. After an induction phase of ca. 4 hours and depending on the stimulus, IL-1ra accumulated linearly for periods up to 96 h. IL-1ra levels in synovial fluids of 19 patients suffering from various inflammatory joint diseases were compared with the cytokine levels of IL-1 beta, IL-6, IL-8, and TNF-alpha. Highest positive correlations were found with IL-8 and IL-1 beta. In normal blood donors IL-1ra serum levels were 150-800 pg/ml (Median: 387 pg/ml). Owing to its sensitivity and large measuring range the newly developed assays appear to be suitable for measuring IL-1ra in cell cultures as well as in biological fluids.

Primary structure of N-linked carbohydrate chains of a human chimeric plasminogen activator K2tu-PA expressed in Chinese hamster ovary cells.

A recombinant human plasminogen activator hybrid variant K2tu-PA, expressed in Chinese hamster ovary cells, is partially glycosylated at Asn12 (A chain, kringle-2 domain) and completely glycosylated at Asn247 (B chain, protease domain). After release of the N-linked carbohydrate chains by peptide-N4-(N-acetyl-beta-glucosaminyl)asparagine amidase F, the oligosaccharides were separated from the protein by gel permeation chromatography, then fractionated by FPLC on Mono Q, followed by HPLC on Lichrosorb-NH2, and analysed by 500-MHz 1H-NMR spectroscopy. The following types of carbohydrates occur: monosialylated diantennary (8%), disialylated diantennary (45%), disialylated tri- and tri'-antennary (1%), trisialylated tri- and tri'-antennary (28%), and tetrasialylated tetra-antennary (18%) structures, all having fucose in alpha(1-6)-linkage at the Asn-bound N-acetylglucosamine. Sialic acid occurred exclusively in alpha(2-3)-linkage to galactose, and consisted of N-acetylneuraminic acid (94%), N-glycolylneuraminic acid (3%), and N-acetyl-9-O-acetylneuraminic acid (3%). In addition, glycopeptide fragments corresponding with the A or B chain of K2tu-PA were analysed. The oligosaccharides attached to Asn12 are less processed than those attached to Asn247. Comparison of the glycosylation pattern of K2tu-PA with that of tissue-type plasminogen activator from different biological sources showed significant differences. Profiling studies on different K2tu-PA production batches demonstrated that the structures of N-linked oligosaccharides were identical, but that relative amounts vary with the applied isolation procedure of the chimeric glycoprotein.

Functional effects of kringle 2 glycosylation in a hybrid plasminogen activator.

uK2t-PA is a hybrid plasminogen activator in which the epidermal growth factor-like domain of the urokinase-type plasminogen activator precedes the kringle 2 and catalytic domains of tissue-type plasminogen activator. The molecules are expressed in Chinese hamster ovary cells in two variant forms, a type II form in which only the protease domain is glycosylated, and a type I form in which both the kringle 2 and the protease domains carry N-acetyllactosamine type glycans. The two forms differed slightly in their affinity for fibrin and fibrinogen, which allowed their separation, but the stimulation of plasminogen activation of the type II form by fibrin was up to eight-fold lower than that of the type II form. The sensitivity to fibrin could be restored by treatment of the type I form with N-glycanase or sialidase. Enzymatic activity vs low molecular weight substrates was not influenced by the glycosylation of kringle 2.

Receptor binding and biological activity of IL-1 alpha, IL-1 beta, IL-1 beta analogues and an IL-1 antagonist in A375 human melanoma cells.

A receptor binding assay for IL-1 peptides on human melanoma cells of the A 375 cell line is reported. Strains differing in their sensitivity to the cytotoxic effects of IL-1 beta were compared. In both strains, binding equilibrium at temperatures between 0 degrees and 37 degrees C was reached after 4 to 8 hours. At 37 degrees C, most of the bound ligand was rapidly internalized leaving a constant level of surface receptors. Scatchard analysis at 0 degrees C revealed a single class of high affinity receptors with a similar KD in both IL-1 resistant (0.18 +/- 0.07 nM) and sensitive strains (0.14 +/- 0.06 nM) but a 10-fold difference in the number of binding sites. Whereas > 1000 binding sites per cell were regularly observed in all resistant strains, only 100-200 sites could be detected on the IL-1 sensitive cells. In displacement assays, IL-1 beta was found to be slightly more potent than IL-1 alpha in both strains. In an attempt to further characterize the IL-1 binding site in these cells, the binding characteristics and biological activity of 20 point mutations of IL-1 beta were examined. EC50 values similar to those of the wild type peptide were found in all these analogues with the exception R11S and E128K: their EC50 was increased by a factor of 10 but the biological activity was reduced 1000-fold as compared to IL-1 beta. The relative potency of an IL-1 receptor antagonist was similar to that of IL-1 beta in the displacement binding assay but a 100-fold higher concentration was required to completely block the cytotoxic effects of IL-1 beta. These results show that A375 human melanoma cells are useful for screening the binding and biological properties of analogues of the IL-1 family of peptides.