Interaction of Cholera Toxin B-subunit with Human T-lymphocytes

In this work, ¹²⁵I-labeled cholera toxin B-subunit (CT-B) (specific activity 98 Ci/mmol) was prepared, and its high-affinity binding to human blood T-lymphocytes (K_d = 3.3 nM) was determined. The binding of the ¹²⁵I-labeled CT-B was inhibited by unlabeled interferon-α₂ (IFN-α₂), thymosin-α₁ (TM-α₁), and by the synthetic peptide LKEKK, which corresponds to sequences 16-20 of human TM-α₁ and 131-135 of IFN-α₂ (K_i 0.8, 1.2, and 1.6 nM, respectively), but was not inhibited by the unlabeled synthetic peptide KKEKL with inverted sequence (K_i > 1 µM). In the concentration range of 10-1000 nM, both CT-B and peptide LKEKK dose-dependently increased the activity of soluble guanylate cyclase (sGC) but did not affect the activity of membrane-bound guanylate cyclase. The KKEKL peptide tested in parallel did not affect sGC activity. Thus, the CT-B and peptide LKEKK binding to a common receptor on the surface of T-lymphocytes leads to an increase in sGC activity.

Thermodynamic, conformational and functional properties of the human C1q globular heads in the intact C1q molecule in solution

Thermodynamic. conformational and functional properties of the human C1q globular heads (hgC1q) were studied with the experimental approaches, which allow investigating these properties in the intact hC1q molecule in solution. Surprisingly, the scanning calorimetry data reveal a low level of cooperativity of interactions between the hgC1q A, B and C domains even at a neutral pH area. Ionization of His residues due to acidification of the medium at the pH range from 6 to 5 or the chemical modification of His residues completely abolishes the cooperative interactions between the domains without significant effect on their conformation. The thermodynamic data provide evidence that the hgC1q module is composed of three structurally independent A, B and C globular domains characterized by the practically identical thermal stability and very similar enthalpy of melting. The spectroscopic studies and modification with 2-oxy-5-nitrobenzylbromide (ONBB) indicate that Trp residues in the hgC1q A and C domains are accessible to the solvent that has been confirmed by the hgC1q crystal structure solved and refined to 1.9 A. The modification of Trp residues significantly affects the complement-dependent cytotoxicity without noticeable effect on the hC1q conformation. These data provide evidence that Trp residues are the components of immunoglobulin-binding sites both in the hgC1q A and C domains.

Synthetic peptide VKGFY and its cyclic analog stimulate macrophage bactericidal activity through non-opioid beta-endorphin receptors

We synthesized linear and cyclic pentapeptides corresponding to the sequence 369-373 of human immunoglobulin G heavy chain--VKGFY (referred to as pentarphin and cyclopentarphin, respectively). The effect of pentarphin and cyclopentarphin on phagocytosis of Salmonella typhimurium virulent 415 strainbacteria by mouse peritoneal macrophages in vitro was studied. Control experiments showed that macrophages actively captured these bacteria, but did not digest them: the captured microbes were viable and continued to proliferate inside the phagocytes; within 12 h all macrophage monolayer was destroyed (incomplete phagocytosis). If 1 nM pentarphin or cyclopentarphin was added to the cultivation medium, macrophage bactericidal activity was significantly increased and they digested all captured microorganisms within 6 h (complete phagocytosis). To study the receptor binding properties of pentarphin and cyclopentarphin we prepared (125)I-labeled pentarphin (179 Ci/mmol specific activity). The binding of (125)I-labeled pentarphin to mouse peritoneal macrophages was high-affinity (K(d) = 3.6 +/- 0.3 nM) and saturable. Studies on binding specificity revealed that this binding was insensitive to naloxone and [Met(5)]enkephalin, but completely inhibited by unlabeled cyclopentarphin (K(i) = 2.6 +/- 0.3 nM), immunorphin (K(i) = 3.2 +/- 0.3 nM), and beta-endorphin (K(i) = 2.8 +/- 0.2 nM). Thus, the effects of pentarphin and cyclopentarphin on macrophages are mediated by naloxone-insensitive receptors common for pentarphin, cyclopentarphin, immunorphin, and beta-endorphin.

Donor strand complementation mechanism in the biogenesis of non-pilus systems

The F1 antigen of Yersinia pestis belongs to a class of non-pilus adhesins assembled via a classical chaperone-usher pathway. Such pathways consist of PapD-like chaperones that bind subunits and pilot them to the outer membrane usher, where they are assembled into surface structures. In a recombinant Escherichia coli model system, chaperone-subunit (Caf1M:Caf1n) complexes accumulate in the periplasm. Three independent methods showed that these complexes are rod- or coil-shaped linear arrays of Caf1 subunits capped at one end by a single copy of Caf1M chaperone. Deletion and point mutagenesis identified an N-terminal donor strand region of Caf1 that was essential for polymerization in vitro, in the periplasm and at the cell surface, but not for chaperone-subunit interaction. Partial protease digestion of periplasmic complexes revealed that this region becomes buried upon formation of Caf1:Caf1 contacts. These results show that, despite the capsule-like appearance of F1 antigen, the basic structure is assembled as a linear array of subunits held together by intersubunit donor strand complementation. This example shows that strikingly different architectures can be achieved by the same general principle of donor strand complementation and suggests that a similar basic polymer organization will be shared by all surface structures assembled by classical chaperone-usher pathways.

beta-Endorphin-like peptide SLTCLVKGFY is a selective agonist of nonopioid beta-endorphin receptor

It has been found that beta-endorphin (beta-END) and a synthetic beta-END-like decapeptide Ser-Leu-Thr-Cys-Leu-Val-Lys-Gly-Phe-Tyr (termed immunorphin, IMN) corresponding to the sequence 364-373 of human IgG heavy chain stimulate Con A-induced proliferation of T lymphocytes from the blood of healthy donors. [Met(5)]enkephalin ([Met(5)]ENK) and an antagonist of opioid receptors naloxone (NAL) tested in parallel were not active. The stimulating effect of beta-END and IMN on T lymphocyte proliferation was not inhibited by NAL. Studies on receptor binding of (125)I-labeled IMN to T lymphocytes revealed that it binds with high affinity to NAL-insensitive binding sites (K(d) = 7.0 +/- 0.3 nM). Unlabeled beta-END completely inhibited the specific binding of (125)I-labeled IMN to NAL-insensitive binding sites on T lymphocytes (K(i) = 1.1 +/- 0.2 nM). Thus, beta-END and IMN bind to common NAL-insensitive binding sites on T lymphocytes and enhance Con A-induced proliferation of these cells.

Synthetic beta-endorphin-like peptide immunorphin binds to non-opioid receptors for beta-endorphin on T lymphocytes

The synthetic decapeptide H-SLTCLVKGFY-OH (termed immunorphin) corresponding to the sequence 364-373 of the CH3 domain of human immunoglobulin G heavy chain was found to compete with [125I]beta-endorphin for high-affinity receptors on T lymphocytes from the blood of healthy donors (K(i) = 0.6 nM). Besides immunorphin, its synthetic fragments H-Val-Lys-Gly-Phe-Tyr-OH (K(i) = 15 nM), H-Leu-Val-Lys-Gly-Phe-Tyr-OH (K(i) = 8.0 nM), H-Cys-Leu-Val-Lys-Gly-Phe-Tyr-OH (K(i) = 3.4 nM), H-Thr-Cys-Leu-Val-Lys-Gly-Phe-Tyr-OH (K(i) = 2.2 nM), H-Leu-Thr-Cys-Leu-Val-Lys-Gly-Phe-Tyr-OH (K(i) = 1.0 nM) possessed the ability to inhibit specific binding of [125I]beta-endorphin to T lymphocytes. Tests of the specificity of the receptors revealed that they are not sensitive to naloxone and Met-enkephalin, i.e. they are not opioid receptors. K(d) values characterizing the specific binding of 125I- labeled immunorphin and its fragment H-Val-Lys-Gly-Phe-Tyr-OH to the receptors have been determined to be 7.4 nM and 36.3 nM, respectively.

Secretion of recombinant proteins via the chaperone/usher pathway in Escherichia coli

F1 antigen (Caf1) of Yersinia pestis is assembled via the Caf1M chaperone/Caf1A usher pathway. We investigated the ability of this assembly system to facilitate secretion of full-length heterologous proteins fused to the Caf1 subunit in Escherichia coli. Despite correct processing of a chimeric protein composed of a modified Caf1 signal peptide, mature human interleukin-1beta (hIL-1beta), and mature Caf1, the processed product (hIL-1beta:Caf1) remained insoluble. Coexpression of this chimera with a functional Caf1M chaperone led to the accumulation of soluble hIL-1beta:Caf1 in the periplasm. Soluble hIL-1beta:Caf1 reacted with monoclonal antibodies directed against structural epitopes of hIL-1beta. The results indicate that Caf1M-induced release of hIL-1beta:Caf1 from the inner membrane promotes folding of the hIL-1beta domain. Similar results were obtained with the fusion of Caf1 to hIL-1beta receptor antagonist or to human granulocyte-macrophage colony-stimulating factor. Following coexpression of the hIL-1beta:Caf1 precursor with both the Caf1M chaperone and Caf1A outer membrane protein, hIL-1beta:Caf1 could be detected on the cell surface of E. coli. These results demonstrate for the first time the potential application of the chaperone/usher secretion pathway in the transport of subunits with large heterogeneous N-terminal fusions. This represents a novel means for the delivery of correctly folded heterologous proteins to the periplasm and cell surface as either polymers or cleavable monomeric domains.

Influence of synthetic peptide corresponding to the ACTH-like sequence of human immunoglobulin G1 on activity of murine thymocytes and peritoneal macrophages

The purpose of the present study was to investigate properties and mechanism of action of the synthetic adrenocorticotropin (ACTH)-like peptide VKKPGSSVKV, corresponding to the sequence 11-20 of the variable part of human immunoglobulin G1 (IgG1) heavy chain. The ACTH-like peptide was shown to act as an immunosuppressive agent in vitro: it inhibits the blast transformation of mouse thymocytes and reduces the spontaneous motility of mouse peritoneal macrophages as well as their bactericidal activity against Salmonella typhimurium 415 virulent strain bacteria. High affinity receptors for the ACTH-like peptide were found on thymocytes and macrophages and shown to be at the same time the receptors for ACTH. The kinetic characteristics of the ACTH-like peptide and 125I-labeled ACTH (13-24) (ACTH 'address segment') specific binding to the receptors were determined. It was found that the ACTH-like peptide binding to the receptors on target cells is accompanied by an increase in both adenylate cyclase activity and intracellular cAMP content.

Influence of synthetic peptide corresponding to the ACTH-like sequence of human immunoglobulin G1 on proliferation of lymphoblastoid cells

Influence of the ACTH-like peptide H-Val-Lys-Lys-Pro-Gly-Ser-Ser-Val-Lys-Val-OH corresponding to the sequence 11-20 of the variable part of human immunoglobulin G1 (IgG1) heavy chain on growth of MT-4 human T-lymphoblastoid cell line was investigated. It was found that the ACTH-like peptide at concentration range 10(-11) -10(-7) M inhibits the proliferation of MT-4 cells. Labeled ACTH 'address segment' [(125)I]ACTH (13-24) was used to establish that MT-4 cells express specific receptors for ACTH (K(d) = 97 pM). The ACTH-like peptide and human ACTH (but not IgG1 heavy chain) were shown to compete with [(125)I]ACTH (13-24) for binding to these receptors (K(i1) = 0.38 nM and K(i2) = 0.34 nM).

Study of immunosuppressive activity of a synthetic decapeptide corresponding to an ACTH-like sequence of human immunoglobulin G1

The synthetic ACTH-like decapeptide H-Val-Lys-Lys-Pro-Gly- Ser-Ser-Val-Lys-Val-OH, corresponding to amino acid residues 11-20 of the variable part of the human IgG1 heavy chain (referred to as immunocortin) was found to have an immunosuppressive effect on cells in vitro: it inhibits blast transformation of mouse thymocytes and reduces spontaneous motility of mouse peritoneal macrophages as well as their bactericidal activity against the virulent bacterial strain Salmonella typhimurium 415. Tritium-labeled immunocortin binds with high affinity to ACTH receptors on thymocytes and macrophages (Kd 2. 1 and 2.5 nM, respectively) and activates adenylate cyclase in these cells. Thus, the interaction of immunocortin with the target cell includes the following main steps: binding to the receptor, activation of adenylate cyclase, and elevation of the intracellular content of cAMP.

Structural and functional significance of the FGL sequence of the periplasmic chaperone Caf1M of Yersinia pestis

The periplasmic molecular chaperone Caf1M of Yersinia pestis is a typical representative of a subfamily of specific chaperones involved in assembly of surface adhesins with a very simple structure. One characteristic feature of this Caf1M-like subfamily is possession of an extended, variable sequence (termed FGL) between the F1 and subunit binding G1 beta-strands. In contrast, FGS subfamily members, characterized by PapD, have a short F1-G1 loop and are involved in assembly of complex pili. To elucidate the structural and functional significance of the FGL sequence, a mutant Caf1M molecule (dCaf1M), in which the 27 amino acid residues between the F1 and G1 beta-strands had been deleted, was constructed. Expression of the mutated caf1M in Escherichia coli resulted in accumulation of high levels of dCaf1M. The far-UV circular dichroism spectra of the mutant and wild-type proteins were indistinguishable and exhibited practically the same temperature and pH dependencies. Thus, the FGL sequence of Caf1M clearly does not contribute significantly to the stability of the protein conformation. Preferential cleavage of Caf1M by trypsin at Lys-119 confirmed surface exposure of this part of the FGL sequence in the isolated chaperone and periplasmic chaperone-subunit complex. There was no evidence of surface-localized Caf1 subunit in the presence of the Caf1A outer membrane protein and dCaf1M. In contrast to Caf1M, dCaf1M was not able to form a stable complex with Caf1 nor could it protect the subunit from proteolytic degradation in vivo. This demonstration that the FGL sequence is required for stable chaperone-subunit interaction, but not for folding of a stable chaperone, provides a sound basis for future detailed molecular analyses of the FGL subfamily of chaperones.

Thiol/disulfide exchange between small heat shock protein 25 and glutathione

Murine small heat shock protein 25 (Hsp25) carries a single Cys-residue at position 141 of its amino acid sequence. In glutathione redox buffers, Hsp25 equilibrates between reduced protein (PSH), mixed disulfide (PSSG) and protein dimer (PSSP) forms. At highly oxidative conditions, native Hsp25 predominantly forms PSSP while denatured Hsp25 forms PSSG. Conversion of PSSP to PSSG correlates with urea and temperature denaturation of tertiary and/or quaternary structure of Hsp25. At pH 7.5, 25 degreesC, the second-order rate constant for the formation of PSSP in the reaction of native PSH with GSSG is 20.1+/-1.4 M-1 min-1. This is approximately 3-fold lower than the reaction velocity of GSSG with a typical, unhindered thiol of pKa 8.6. At redox equilibrium, the fractions of PSSP, PSSG, and PSH depend on the concentration of GSH and less on the ratio [GSH]/[GSSG] (R). At a constant R, the fractions of PSSG and PSH species depend similarly on GSH concentration, being approximately equal in glutathione redox buffers with low R. It is concluded that in oligomeric complexes, Hsp25 subunits in vitro form stable dimers, in which the reacting -SH groups are in a proximity to form intersubunit disulfide bonds. Within a reaction of one of these -SH groups with GSSG, steric hindrances and electrostatic repulsion complicate penetration of another reduced or oxidized glutathione molecule to the reaction site.

Analogous conformations of both binding and effector regions in cyclosporin A, FK506 and rapamycin

Three immunosuppressant drugs, cyclosporin A, FK506 and rapamycin were compared in their three-dimensional structures by computer modelling. The pairwise comparisons of cyclosporin A, FK506 and rapamycin show two structurally common fragments. One fragment is Mle9-Bmt1 region in cyclosporin A, C22-O5 region in FK506 and C29-O5 region in rapamycin. Another fragment is Mle4-Mle6 region in cyclosporin A and C14-C21 regions in FK506 and rapamycin. The correspondence of the structurally analogous regions with the regions which are involved in the interactions with peptidyl-prolyl cis/trans isomerases and calcineurin or FKBP-rapamycin-associated protein is discussed.

Influence of L-glutamic acid on binding of interleukin-1beta, tumour necrosis factor-alpha and interleukin-6 to HL-60 cells

To elucidate the mechanism of differentiating activity on L-Glu to HL-60 cells, its influence on binding of human recombinant interleukine-1beta (rHuIL-1beta), tumour necrosis factor-alpha (rHuTNF-alpha) and interleukine-6 (IL-6) by HL-60 cells was studied. It was established, that L-Glu converted the high affinity binding of [125I]rHuIL-1beta (Kd = 0.32 nM) and [125I]rHuIL-6 (Kd = 0.075 nM) to HL-60 cells into low affinity (corresponding Kd values -13.3 and 2.1 nM) at concentration 0.1 microM. The preincubation for an hour of HL-60 cells with 0.1 microM L-Glu was shown to result in an increase of affinity and number of [125I]rHuTNF-alpha binding sites. Thus, L-Glu decreases the sensitivity of the HL-60 cells to IL-1beta and IL-6 and increases TNF-alpha binding at concentration 0.1 microM.

Investigation of the cooperative structure of Fc fragments from myeloma immunoglobulin G

The cooperative structure of Fc fragments prepared from myeloma human IgG1 was studied using scanning microcalorimetry and fluorescence at pH 4.2-8.0. It was shown that the first to be melted are CH2 domains whose interaction with each other is rather weak, while that with CH3 domains is strong. Then CH3 domains which form a single cooperative block are melted. The data for the structure of the Fc fragment in solution agree with the X-ray data according to which the interaction between CH2 domains is mediated by the carbohydrate moiety while the two CH3 domains are strongly associated. The presence of intensive CH2-CH3 interaction is a distinctive feature of the state of the Fc fragment in the given pH region as compared to that at pH <4.1 [Tischenko, V. M., et al. (1982) Eur. J. Biochem. 126, 517-521; Ryazantsev, S., et al. (1990) Eur. J. Biochem. 190, 393-399]. First, cis interactions greatly increase the free energy of the native structure stabilization in CH2 domains. Second, they decrease this energy for CH3 domains when compared to the state of the latter at pH 3.8 or within the Fc' fragment (the dimer of CH3 domains). The temperature and enthalpy of melting of CH2 domains coincide in all the samples studied despite heterogeneity of the carbohydrate moiety. Thus, it may be postulated that the conservative part of CH2 domains makes a cardinal contribution to the interaction of these domains with the carbohydrate moiety.

Molecular models of two competitive inhibitors, IL-2delta2 and IL-2delta3, generated by alternative splicing of human interleukin-2

Molecular models of IL-2delta2 and IL-2delta3, two alternative splice variants of human IL-2 without exon 2 and 3, respectively, are described. These alternative splice variants attract particular interest as potential competitive inhibitors of the cytokine. Tertiary structure of IL-2 consists of four-helix bundle including helices A, B, C and D and a beta-pleated sheet. Exon 2 encodes the A-B loop (Asn30-Lys49 residues) linking helices A and B running in one direction. Rotation of the helix A around putative centre during the construction of IL-2delta2 model have not produced any significant changes in the hydrophobic core of IL-2 molecule. However, a large hole was formed on the surface of IL-2delta2 molecule instead of A-B loop in IL-2 fold. A high affinity IL-2 receptor is formed by combination of alpha, beta, and gamma(c) chains. Comparison of the model of the receptor bound IL-2 with the model of IL-2delta2 has shown that their beta-chain binding sites have minimum differences as distinct from alpha and gamma(c) chain-binding sites. Exon 3 encodes Ala50-Lys97 fragment which forms helices B and C with their short connecting loop. Model IL-2delta3 consists of helices A and D and long linking loop. This loop was composed of A-B and C-D loops which run in opposite directions in IL-2 structure and contain beta-strands making a beta-pleated sheet. Conformation of the linking loop relatively to helices A and D was stabilized by creation of a disulphide bond between cysteines 105 and 125. In addition, the hydrophobic residues of beta-sheet interact with the hydrophobic surface of A-D helical complex and close the latter from contacts with solution. Comparison of the model of IL-2 bound to receptor with IL-2delta3 model has shown that absence of helices B and C in IL-2delta3 model results in insignificant conformational changes only in residues interacting with gamma(c) chain of the receptor. The beta/gamma(c) heterodimer is an intermediate affinity receptor of IL-2. Most likely, both IL-2delta2 and IL-2delta3 are naturally occurring IL-2 antagonists since they keep the ability of binding with an intermediate affinity receptor of this cytokine and fail to engage the alpha chain of its high affinity receptor.

Molecular model of an alternative splice variant of human IL-4, IL-4 delta 2, a naturally occurring inhibitor of IL-4-stimulated T cell proliferation

The molecular model of IL-4 delta 2, a naturally occurring splice variant of human IL-4 with exons 1, 3, and 4 in an open reading frame, is described. The second exon codes the main part of the long loop AB connected the helices A and B in parallel superposition. Therefore the hydrophobic core and the native fold of the rest part of IL-4 delta 2 molecule could be preserved without any significant changes only in the case of revolution of the helix A relative to other helices. In the result, the dominated a left-handed four-helix bundle structure of IL-4 with an up-up-down-down structural pattern is transformed to the IL-4 delta 2 structure with a down-up-down-down structural pattern.

Influence of the conserved disulphide bond, exposed to the putative binding pocket, on the structure and function of the immunoglobulin-like molecular chaperone Caf1M of Yersinia pestis

The Yersinia pestis protein Caf1M is a typical representative of a subfamily of periplasmic molecular chaperones with characteristic structural and functional features, one of which is the location of two conserved cysteine residues close to the putative binding pocket. We show that these residues form a disulphide bond, the reduction and alkylation of which significantly increases the dissociation constant of the Caf1M-Caf1 (where Caf 1 is a polypeptide subunit of the capsule) complex [from a Kd of (4.77+/-0.50)x10(-9) M for the intact protein to one of (3.68+/-0.68)x10(-8) M for the modified protein]. The importance of the disulphide bond for the formation of functional Caf1M in vivo was demonstrated using an Escherichia coli dsbA mutant carrying the Y. pestis f1 operon. In accordance with the CD and fluorescence measurements, the disulphide bond is not important for maintenance of the overall structure of the Caf1M molecule, but would appear to affect the fine structural properties of the subunit binding site. A three-dimensional model of the Caf1M-Caf1 complex was designed based on the published crystal structure of PapD (a chaperone required for Pap pili assembly) complexed with a peptide corresponding to the C-terminus of the papG subunit. In the model the disulphide bond is in close proximity to the invariant Caf1M Arg-23 and Lys-142 residues that are assumed to anchor the C-terminal group of the subunit. The importance of this characteristic disulphide bond for the orchestration of the binding site and subunit binding, as well as for the folding of the protein in vivo, is likely to be a common feature of this subfamily of Caf1M-like chaperones. A possible model for the role of the disulphide bond in Caf1 assembly is discussed.

Structure of cytokine hydrophobic cores

Diagrams were constructed that describe, using a common frame of reference, the interactions that occur within the hydrophobic cores of the left-handed four-helix bundles of interleukin-2, -4, -5, granulocyte/macrophage-, granulocyte-, macrophage-colony-stimulating factor, beta- and gamma-interferon, growth hormone, and leukemia inhibitory factor. Based on the assumption that the topologies of the ligand-receptor complexes are similar, analogous patterns were obtained from these diagrams and lead to the detailed comparison of the hydrophobic cores. These patterns were then used to obtain pairwise rigid-body superpositions among all of the four-helix bundles; values of the root-mean-square deviations (C alpha-atoms) over the four alpha-helices of the bundles range from 1.14 A to 3.22 A. Two distinct groups are formed after clustering based on structural superposition of the ten cytokines.

pH6 antigen (PsaA protein) of Yersinia pestis, a novel bacterial Fc-receptor

It was found that recombinant pH6 antigen (rPsaA protein) forming virulence-associated fimbriae on the surface of Yersinia pestis at pH 6.7 in host macrophage phagolysosomes or extracellularly in abscesses such as buboes, is a novel bacterial Fc-receptor. rPsaA protein displays reactivity with human IgG1, IgG2 and IgG3 subclasses but does not react with rabbit, mouse and sheep IgG.

Conservative hydrophobic interdomain contacts of IFN-gamma remain in P17 matrix protein of HIV-1

A constructed scheme of the surface layers containing helices C, D, and E' of various polypeptide chains which participate in the interdomain contacts in IFN-gamma demonstrated two sites of localization of the conservative hydrophobic amino acids. An analogous scheme of the interaction of helices B, C, and D in the p17 matrix protein of HIV-1 showed that the majority of the hydrophobic positions are similar. These data confirm the structural similarity between p17 and IFN-gamma.

The de novo protein with grafted biological function: transferring of interferon blast-transforming activity to albebetin

The de novo protein albebetin has been designed recently to form a predetermined tertiary fold that has not yet been observed in natural proteins. An eight amino acid fragment (131-138) of human interferon alpha(2) carrying the blast-transforming activity of the protein was attached to the N-terminus of albebetin next to its initiatory methionine residue. The gene of chimeric protein was expressed in a wheat germ cell-free translation system and synthesized protein was tested for its compactness and stability. Its ability for receptor binding was also studied. We have shown that albebetin with attached octapeptide is practically as compact as natural proteins of corresponding molecular weight and possesses high stability toward the urea-induced unfolding. It binds murine thymocyte receptor at a high affinity and activates the thymocyte blast transformation efficiently at a concentration of 10(-11) M.

Receptor-binding properties of the peptides corresponding to the beta-endorphin-like sequence of human immunoglobulin G

The decapeptide H2N-Ser-Leu-Thr-Cys-Leu-Val-Lys-Gly-Phe-Tyr-COOH (termed immunorphin) corresponding to the sequence 364-373 of the CH3 domain of the human immunoglobulin G1 Eu heavy chain and displaying a 43% identity with the antigenic determinant of beta-endorphin was synthesized. Immunorphin was found to compete with 125I-beta-endorphin for high-affinity receptors on murine peritoneal macrophages (K = 2.5 +/- 0.9 x 10(-9) M) and with 3H-morphin for receptors on murine thymocytes (Ki = 2.7 +/- 0.6 x 10(-9) M) and murine macrophages (Ki = 5.9 +/- 0.7 x 10(-9) M). In particular two types of receptors to 125I-beta-endorphin with Kd1 = 6.1 +/- 0.6 x 10(-9) M and Kd2 = 3.1 +/- 0.2 x 10(-8) M were revealed on macrophages. The second type of receptors interacted with 125I-beta-endorphin, 3H-Met-enkephalin, 3H-Leu-enkephalin and 3H-morphin; the first displayed reactivity with 125I-beta-endorphin, 3H-morphin and immunorphin. The first type receptors are not present on murine brain cells nor are inhibited by naloxone. A minimum fragment of immunorphin practically completely retaining its inhibitory activity in the competition tests with 125I-beta-endorphin for common receptors on thymocytes was found to correspond to the tetrapeptide H2N-Lys-Gly-Phe-Tyr-COOH (Ki = 5.6 +/- 0.5 x 10(-9) M).

Dimer structure as a minimum cooperative subunit of small heat-shock proteins

Recently, it has been shown that small heat-shock proteins (Hsp25, Hsp27) are molecular chaperones. They bind to thermally unfolded proteins and can also assist refolding of denatured proteins. Mammalian small Hsps can form oligomeric structures of about 32 subunits. Until now, no data about cooperativity and stability of the interactions between the subunits of sHsps are available. To analyze these interactions we studied mouse Hsp25 and human Hsp27 by difference adiabatic scanning microcalorimetry (DASM) and circular dichroism (CD). Here we show that, according to DASM data, the minimum cooperatively melting structure is a sHsp-dimer. CD data indicate that Hsp25 major secondary structure, the beta-pleated conformation, is resistant to acidic influence up to pH 4.5 and, at neutral pH values, to heat treatment up to 60 degrees C. The melting pattern of Hsp25/27 bears resemblance to alpha-crystallins. CD data indicate similar secondary, tertiary and quaternary structures of the proteins compared. This finding is in agreement with the revealed homology of primary structure of these proteins and their common chaperone function.

Specific high affinity binding of human interleukin 1 beta by Caf1A usher protein of Yersinia pestis

Understanding the interaction of Yersinia pestis with the key components of the immune system is important for elucidation of the pathogenesis of bubonic plague, one of the most severe and acute bacterial diseases. Here we report the specific, high affinity binding (Kd = 1.40 x 10(-10) M +/- 0.14 x 10(-10)) of radiolabelled human interleukin 1 beta (hIL-1 beta) to E. coli cells carrying the capsular f1 operon of Y. pestis. Caf1A outer membrane usher protein was isolated to greater than 98% purity. Competition studies with purified Caf1A, together with immunoblotting studies, identified Caf1A as the hIL-1 beta receptor. Competition between Caf1 subunit and hIL-1 beta for the same or an overlapping binding site on Caf1A was demonstrated. Relevance of these results to the pathogenesis of Y. pestis and other Gram negative bacterial pathogens with homologous outer membrane usher proteins is discussed.

Structural and functional homology between periplasmic bacterial molecular chaperones and small heat shock proteins

The periplasmic Yersinia pestis molecular chaperone Caf1M belongs to a superfamily of bacterial proteins for one of which (PapD protein of Escherichia coli) the immunoglobulin-like fold was solved by X-ray analysis. The N-terminal domain of Caf1M was found to share a 20% amino acid sequence identity with an inclusion body-associated protein IbpB of Escherichia coli. One of the regions that was compared, was 32 amino acids long, and displayed more than 40% identity, probability of random coincidence was 1.2 x 10(-4). IbpB is involved in a superfamily of small heat shock proteins which fulfil the function of molecular chaperone. On the basis of the revealed homology, an immunoglobulin-like one-domain model of IbpB three-dimensional structure was designed which could be a prototype conformation of sHsp's. The structure suggested is in good agreement with the known experimental data obtained for different members of sHsp's superfamily.

Some new aspects of molecular mechanisms of cyclosporin A effect on immune response

A few protein targets were found to display a specific high-affinity interaction with the immunosuppressant cyclosporin A (CsA): cytosolic cyclophilins (CyP)A, B, C, D, E containing from 122 to 174 amino acid residues in a polypeptide chain, and secreted forms of CyP; CyP-40, 40-kDa CsA-binding polypeptide complexed with steroid receptor (SR); CyP-related 150-kDa receptor of natural killer (NK) cells; interleukin 8 (IL-8); actin; a family of molecular chaperones hsp70 and P-glycoprotein (P-GP). All CyPs possess peptidyl-prolyl cis-trans isomerase activity (PPIase) and may serve as ATP-independent molecular chaperone proteins. The CsA-CyP complexes are specific inhibitors of Ca(2+)-and calmodulin-dependent protein phosphatase calcineurin (CaN). The inhibition of CaN blocks the activation of genes of IL-2, IL-2R, IL-4, etc. in T cells. In addition, immunosuppressive and/or antiinflammatory activity of CsA can be executed via CyP-40 and hsp 70 complexed with SR, and following the interaction with CyP-related receptor of NK and with IL-8. CsA binding to CyPC, P-GP and actin may throw light on the biochemical events leading to nephrotoxicity and graft vessel disease, two major side effects produced by CsA. The discovery of the interaction of human immunodeficiency virus type 1 (HIV-1) Gag protein with CyP and effective disruption of this interaction by CsA may be important for our understanding of the pathology caused by this immunosuppressive virus and will inspire therapeutic strategies to nip HIV in the bud. Bacterial immunophilins (ImPs) contribute to the virulence of pathogenic microorganisms. Elucidation of molecular mechanisms of microbial ImPs' action in the pathogenesis of bacterial infections may lead to new strategies for designing antibacterial drugs.

Receptor-binding properties of the peptides corresponding to the ACTH-like sequence of human pro-interleukin-1 alpha

The octapeptide Gly-Lys-Val-Leu-Lys-Lys-Arg-Arg (termed leukocorticotropin, LCT) corresponding to the ACTH-like sequence 81-88 of human pro-interleukin-1 alpha and its derivative Tyr-Gly-Lys-Val-Leu-Lys-Lys-Arg-Arg were synthesized. The 125I-labeled Tyr-LCT specifically interacts with one type of receptor on the surface of murine splenocytes (Kd = (1.45 +/- 0.04) x 10(-8) M, the number of binding sites is equal to 4500) and with two types of receptors on the surface of murine peritoneal macrophages (Kd1 = (5.9 +/- 1.0) x 10(-9) M and Kd2 = (2.6 +/- 2.2) x 10(-7) M). LCT and Tyr-LCT significantly increase the adenylate cyclase activity of murine peritoneal macrophages. The receptor binding and adenylate cyclase stimulation activity of LCT and Tyr-LCT are inhibited by ACTH (13-24).

Modelling of steric structure of a periplasmic molecular chaperone Caf1M of Yersinia pestis, a prototype member of a subfamily with characteristic structural and functional features

Steric structure of Caf1M, a periplasmic molecular chaperone of Yersinia pestis, was reconstructed by computer modelling based on a statistically significant primary structure homology between Caf1M and PapD protein from Escherichia coli, and using the known atomic coordinates obtained by the X-ray crystallography for PapD. In the three-dimensional model of Caf1M an accessory sequence between F1 and G1 beta-strands (as compared to PapD) can form a strain-specific part of the binding pocket of surface organell subunits. This accessory sequence decreases the depth of the binding pocket. The characteristic structural feature of the subfamily of periplasmic molecular chaperones with the accessory sequence (Caf1M subfamily) is the existence of exposed to a solvent Cys residues in F1 and G1 beta-strands which can form disulfide bond in the putative binding pocket. The characteristic functional feature of Caf1M subfamily is the chaperoning of more simple compositions of virulence-associated surface organells (in the case of Y. pestis a capsule consists of only F1 protein). Highly conserved R82 and D93, located at the domain surface remote from the putative subunit binding pocket, can participate in direct contacts with the conserved portion of molecular usher proteins.

Modelling of interhelical contacts in interferons-beta, -gamma, and dimeric interleukin-5

On the basis of crystallographic data, the alpha-helices of interferon-beta as well as each domain of interferon-gamma are located in two layers. This results in a different contribution from the amino acids placing in the middle and border alpha-helices of the layer to the hydrophobic core of the molecule. A close analysis of the structure of dimeric interleukin-5 shows related arrangements of alpha-helices. The full schemes of the interhelix contacts of interferons-beta, -gamma, and dimeric interleukin-5 were constructed. Schemes for interleukin-5 show that extension of helices correlates with the dimer topology.

Common structural patterns of cytokine outer surfaces

Schemes of the four-helix bundle surfaces of interleukin-2, -4, -5, granulocyte/macrophage-, granulocyte-, macrophage-colony-stimulating factor, interferon-beta, -gamma and growth hormone were designed. All cytokines appeared to have the structurally similar "holes" on the surfaces. They were suggested to serve as a part of the main receptor-binding sites.

Structural repeats in cyclosporin A

The conformation of various dipeptides of free and cyclophilin A-bound cyclosporin A were compared. Cyclosporin A was shown to contain in both states conformationally duplicated fragments in the putative binding sites for cyclophilin A and phosphatase calcineurin.

Comparison of conformations of cyclosporin A and macrolide FK506 fragments: localization of putative binding sites with phosphatase calcineurin

The three-dimensional structures of two immunosuppressants, cyclosporin A and macrolide FK506, were compared. The sites N-methylglycine3-N-methylleucine4 and valine5-N-methylleucine6 of cyclosporin A were found to be similar to each other (the root-mean-square value was 0.29 A for six reference points of the main chain) and also to the site C17-C22 of FK506 (the root-mean-square values were 0.33 A and 0.13 A, respectively). We suggest these fragments of cyclosporin A and FK506 make a major contribution to the interaction of the immunosuppressants with the phosphatase calcineurin.

Structural similarity of the binding sites of cyclophilin A-cyclosporin A and FKBP-FK506 systems

Two enzymes, cyclophilin A and FK506-binding protein, with similar cis-trans isomerization catalytic activities but no similarity on the amino acid sequence level were compared in their three-dimensional structure by computer modelling. Cyclophilin A and FK506-binding protein proved to have similar arrangements at nine of the amino acids at their active site pockets. Two inhibitory peptides, cyclosporin A and FK506, also have structural similarities at their contact regions to the active sites. The studied systems may be another example of convergent evolution of enzyme catalytic site.

Peptide-mapping of three neutralizing epitopes into predicted biologically active sites of human interferon-alpha 2

Immunologically less reactive but functionally relevant structures were identified on human interferon (IFN)-alpha 2 by three neutralizing monoclonal antibodies (mAb). The binding sites of these mAbs were mapped using a set of synthetic peptides that covered the amino acid sequence of two predicted biologically active segments in the regions 31-53 and 63-85 of IFN-alpha 2. We measured the capacity of fragments to inhibit the IFN-neutralizing activity of mAbs and located three linear epitopes around residues 42-53, 63-76 and 77-85 of the IFN-alpha 2 molecule.

Protein V, a novel type-II IgG receptor from Streptococcus sp.: sequence, homologies and putative Fc-binding site

We have cloned and sequenced the Fc-receptor-encoding gene, fcrV, from a group G streptococcus. Considerable similarity was revealed between the FcRV, FcRA76 and M proteins of group A streptococci in their signal sequences and 3' termini, and between the Fc-binding regions of FcRV and FcRA76. The promoter and terminator regions showed no homology with those of the fcrA76 and M protein-encoding genes. The A1-A4 domains of FcrV (protein V) exhibit a heptapeptide repeat motif which is characteristic of alpha-helical coiled-coil proteins. The sequence, Ser-Asn-Arg-Ala-Ala, in the outer position, 'f' of each domain is highly conserved and may be involved in FcR-IgG interactions.

Immunodominant structures in the aminoterminal portion of human interferon alpha 1

The analysis of the antigenic structure of human interferon (IFN)-alpha 1 with a panel of monoclonal antibodies revealed four immunodominant regions. Three of them, recognized by 12 of 14 antibodies were mapped into the aminoterminal portion of IFN-alpha 1 around residues 31-38, 43-53 and 63-85. The region 31-85 proved important also for the antiviral and antiproliferative activity of the IFN-alpha 1 molecule. The antibody recognizing the sequence around residues (54)63-67 also inhibited the cellular binding of IFN-alpha 1 to the high-affinity receptors.

Caf1R gene and its role in the regulation of capsule formation of Y. pestis

A new transcription unit of the f1 gene cluster was found. The DNA sequencing revealed one long open reading frame. Deletion and frame shift mutation analyses have demonstrated the importance of a corresponding gene product for the F1 antigen biosynthesis. A homology of the deduced amino acid sequence with that of AraC family DNA-binding regulators was shown. A potential regulatory DNA region is discussed.

Nonapeptide corresponding to the sequence 27-35 of the mature human IL-2 efficiently competes with rIL-2 for binding to thymocyte receptors [corrected]

Previously it was shown [1] that amino acid substitutions at the region of the first alpha-helix of IL-2 specifically inactivate its reactivity with the intermediate-affinity receptor p70, and mutations in the fifth alpha-helix specifically inactivate the binding to the low-affinity receptor p55. We have synthesized the peptides corresponding to the putative binding site of IL-2 with the intermediate-affinity receptor p70 and found that the nonapeptide corresponding to the sequence 27-35 of the mature IL-2 [2] effectively competes with human rIL-2 for binding to thymocyte receptors. Two types of nonapeptide receptors were revealed: those with Kd1 = 1.84 x 10(-8) M and Kd2 = 1.6 x 10(-7) M. The rIL-2 provides a 100% inhibitory effect on the binding of the 125I-labeled nonapeptide to thymocyte receptors, Ki = 3.5 x 10(-8) M. Low immunoproliferative activity of the peptide allows one to recommend it as a specific antiproliferation drug, IL-2 inhibitor [corrected].

A new gene of the f1 operon of Y. pestis involved in the capsule biogenesis

The DNA sequence determination of the f1 operon between the genes encoding the F1 subunit (caf1) and chaperone-like protein (caf1M) revealed a large open reading frame that codes for a polypeptide similar to some E. coli proteins involved in the biogenesis of fimbria. The deletion and in trans complementation analyses showed that this gene is not necessary for extracellular transport of the F1 subunit but plays a role in the capsule assembly.

Expression of the envelope antigen F1 of Yersinia pestis is mediated by the product of caf1M gene having homology with the chaperone protein PapD of Escherichia coli

The effective synthesis of the envelope antigen F1 of Y. pestis in E. coli HB101 is mediated by the expression of the caf1M gene. This gene was sequenced, and the protein encoded was found to have a significant homology with the chaperone protein PapD of uropathogenic E. coli. The data presented allow one to suppose Caf1M and PapD proteins perform similar functions in the biogenesis of the Y. pestis capsule and E. coli P-pili, respectively.

Mechanisms of generation of antibody diversity as a cause for natural selection of homoiothermal animals in the process of evolution

The temperature-dependence of domain interactions in the Fab, Fc, Fb and Fv fragments from human myeloma immunoglobulins (IgG) samples was investigated by scanning microcalorimetry, NMR and difference spectroscopy. The fragments were found to be very sensitive to temperature changes. Lowering the temperature below the physiological value (37 degrees C) considerably decreases the energy of interaction of the variable VH and VL domains, resulting at times in their dissociation. Since the association energies of VH and VL pairs can be affected by the result of somatic recombination and mutation events affecting antibody genes, immunoglobulins can fortuitously acquire the properties of cryoglobulins or cold autoantibodies and induce severe pathological states. It is postulated that this property of immunoglobulins, and by extension, of T-cell antigen receptors might have been one of the causes for the possible natural selection of homoiothermal animals. In these, the high conformational sensitivity of immunoglobulins to temperature change may be important in the mechanisms of induction of secondary functions in immune responses.

The octapeptide corresponding to the region of the highest homology between alpha-interferon and thymosin-alpha 1 effectively competes with both cytokines for common high-affinity receptors on murine thymocytes

The octapeptide corresponding to human interferon-alpha 2 (Hu IFN-alpha 2) sequence 131-138 has high affinity to murine thymocyte receptors (Kd = 4.2 x 10(-12) M, about 700 receptors per cell). The peptide receptor binding is inhibited by both Hu rIFN-alpha 2 (Ki = 8.6 x 10(-10) M) and thymosin-alpha 1 (TM-alpha 1) (Ki = 3 x 10(-7) M) as well as by the octapeptide homologous to the TM-alpha 1 sequence 16-23 (Ki = 4.5 x 10(-7) M). The peptide from IFN-alpha 2 (131-138) activates murine thymocyte blast transformation at a concentration of 10(-11) M in the presence of 2.5 micrograms/ml of concanavalin A.

Nucleotide sequence of the Yersinia pestis gene encoding F1 antigen and the primary structure of the protein. Putative T and B cell epitopes

The plasmid-located gene caf1 encoding the capsular antigen fraction 1 (F1) of Yersinia pestis was cloned and sequenced. The gene codes for a 170 amino acid peptide with a deduced Mr of 17.6 kDa. The signal peptide sequence was highly homologous to the E. coli consensus signal sequence. The F1 was assumed to have beta-sheet structure for the most part. The region located between amino acids 100 and 150 was suggested to contain putative antigenic determinants and to stimulate T cells.

Electron microscopy study of human myeloma immunoglobulin G1

Human immunoglobulin G1 Van was studied by negative staining, freeze drying and high resolution shadow casting. The Fab and Fc subunits of an intact IgG1 molecule were shown to possess limited mobility. It was found that about 70% of molecules in the IgG1 Van specimen are not flat but have a tripod-like shape.

Theoretical conformational analysis of a family of alpha-helical immunocytokines

According to the results of the theoretical conformation analysis and available experimental data, the known immunocytokines can be divided into two groups: alpha-helical (IFNs-alpha, beta, gamma, omega; IL-2, 3, 4, 5, 6, 7; G-, M-, GM-CSFs; cMGF, PDGF) and beta-pleated proteins (ILs-1 alpha, beta; TNFS-alpha, beta). IFNs-alpha, beta, gamma, omega, IL-6, G-CSF, cMGF were shown to form a family of alpha-helical globular proteins characterized by a statistically significant homology in amino acid sequences and by common features of the secondary structure formation. Comparison of the sequences of 72 IFNs-alpha, beta, omega reveals three clusters of conservative amino acid positions. Their participation in the formation of active sites of IFN-alpha, beta, omega is supposed.