The peptide molecular links between the central nervous and the immune systems.

The central nervous system (CNS) and the immune system were for many years considered as two autonomous systems. Now, the reciprocal connections between them are generally recognized and very well documented. The links are realized mainly by various immuno- and neuropeptides. In the review the influence of the following immunopeptides on CNS is presented: tuftsin, thymulin, thymopoietin and thymopentin, thymosins, and thymic humoral factor. On the other side, the activity in the immune system of such neuropeptides as substance P, neurotensin, some neurokinins, enkephalins, and endorphins is discussed.

Synthesis, conformation, and immunosuppressive activity of CLX and its analogues.

The CLX peptide isolated from flax seed has a sequence cyclo-(PPFFILLX), where X is a nonproteinaceous amino acid residue, (2S,4R) 4-amine-N-methylproline. Picur, B.; Lisowski, M.; Siemion, I.Z. Letters Pept Sci 1998, 5, 183-187. The structure of X strongly suggests that this natural amino acid plays a role of the dipeptide moiety with a nonplanar cis peptidomimetic bond. The X residue contains two asymmetrical carbons and thus can appear in four configurations: (2S,4R), (2S,4S), (2R,4S), and (2R,4R). All four diastereoisomers of X were synthesized and characterized as trifluoroacetates of 4-phtalimido-N-methylproline benzylamides. Their full physicochemical characteristics are presented in this article. The synthesis of linear and cyclic analogues of CLX containing all four possible diastereoisomers of X was performed. Additionally, analogues with gamma-aminobutyric acid (GABA) and glycyl-N-methyl-glycine dipeptide [G(Me)G] substituted for X were synthesized. The obtained peptides were purified using HPLC, examined by ESI/MS, and then studied by CD spectroscopy. They were also tested for immunosuppressive activity (PFC in vitro). All of them revealed diverse immunosuppressive activity, however, lower than that of cyclolinopeptide A (CLA) Wieczorek, Z.; Bengtsson, B.; Trojnar, J.; Siemion, I.Z. Peptide Res 1991, 4, 275-283. and cyclosporine A (CsA). Ellis, G.P.; West, G.B. Progress Med Chem 1988, 25, 1-33. The structure of CLX with (2S,4R) 4-amino-N-methylproline was determined by 2-D NMR methods. All amide bonds are in the trans configuration. The cis peptidomimetic group delta-CH(2)-N(CH(3))- is exposed to the outside of the CLX molecule. The peptide contains two loops similar to beta-turns of type IV. Chou, P.Y.; Fasman, G.D. J Mol Biol 1977, 115, 136-715 and has the extended shape flanked by F3 and L7 residues with significant side chain flexibility.

Immunosuppressory activity of the cyclodimeric peptide with RGD-sequences.

Our previous studies showed that the nonapeptide fragment of HLA-DQ of the sequence H-Thr-Pro-Gln-Arg-Gly-Asp-Val-Tyr-Thr-OH, located in the beta164-172 loop, strongly suppresses the humoral and cellular immune responses, while its shorter analogs, H-Arg-Gly-Asp-Val-OH, H-Arg-Gly-Asp-Val-Tyr-OH and H-Gln-Arg-Gly-Asp-Val-Tyr-OH show only a weak stimulatory activity in respect to the humoral immunological response. These fragments contain the Arg-Gly-Asp (RGD) sequence, known for its importance for cellular association phenomena. Based on the crystal structure of HLA-DR1, we also designed and synthesized a cyclic analog H-Cys-Arg-Gly-Asp-Val-Tyr-Cys-OH with restricted conformation, which strongly suppresses the immune response and selectively inhibits the alphavbeta3 integrin, suggesting that the mechanism of the immunosuppressory action of the peptide is associated with inhibition of the integrin. In this paper we present the design and synthesis of the cyclodimeric peptide, Arg-Gly-Asp-Arg-Gly-Asp, which is also known as a selective alphavbeta3 inhibitor. The synthesized peptide strongly suppresses both the humoral and cellular immune response. The results support our hypothesis that the immunomodulatory activity of HLA-DQ fragments may be connected with their interactions with some particular integrins on the cell surface.

New hypothesis on amino acid complementarity and its evaluation on TGF-beta(2)-related peptides.

A new hypothesis of amino acid complementarity based on the genetic code periodicity is presented and evaluated on the peptide pairs composed of the fragments of TGF-beta(2) protein (YIGKTPKI and YYIGKTPKIE) and corresponding complementary peptides [IYPLC(Acm)GLY, IIYTLWGLYL, IIYPLC(Acm)GLYL and IIYTLC(Acm)GLYL]. The ESI-MS and CD methods were used for monitoring of the complexation. It was found that heterodimeric structures are formed between the peptides and complementary peptides. No complexation appears in solutions of single components of the systems, nor in solutions containing the mixtures of TGF-beta(2) peptides or complementary peptides. CD measurements suggest that the conformation of peptides needed for complex formation is of the beta-structure type. The binding forces, which stabilize the complexes, consist mainly of hydrophobic interactions.

Design, synthesis and biological evaluation of a new bridged immunosuppressor.

A bridged peptide with the sequence: H-Thr-Pro-Gln-Arg-Gly-Asp-Val-gamma-Abu-Asn-Asp-Gln-Glu-Glu-Thr-Thr-Gly-Val-Val-Ser-Thr-Pro-Leu-Ile-Arg-Asn-Gly-OH was designed to mimic the discontinuous epitope of the HLA-DQ molecule that might interact with CD4. The bridged peptide revealed distinct suppressory effect in the humoral immune response. This result supports our suggestion that the 164-172 region of the HLA-DQ molecule may enhance its interactions with coreceptors, possibly with CD4.

New conformationally restricted analog of the immunosuppressory mini-domain of HLA-DQ and its biological properties.

Our previous studies revealed that the nonapeptide fragment of HLA-DQ located in the beta 164-172 loop of the Thr-Pro-Gln-Arg-Gly-Asp-Val-Tyr-Thr sequence suppresses the immune humoral and cellular responses [30]. Based on the crystal structure of HLA-class II molecules we designed and synthesized a cyclic analog with restricted conformation, cyclo(Suc-Thr-Pro-Gln-Arg-Gly-Asp-Val-Lys)-Thr-OH (Suc = succinyl) by reacting a Lys side chain with a succinylated N-terminus. The cyclization product more potently suppresses the cellular immune response than its linear counterparts and is efficiently cleaved by trypsin. The results indicate that the beta 164-172 loop may serve as a functional epitope on the HLA class II surface for intermolecular binding.

Antimalarial activity of cyclolinopeptide A and its analogues.

Cyclolinopeptide A (CLA) is an immunosuppressive peptide of the sequence c-(-Leu-Ile-Ile-Leu-Val-Pro-Pro-Phe-Phe-), isolated from linseed. Since another cyclic, hydrophobic, immunosuppressive peptide, cyclosporin A, has potent antimalarial activity, CLA and a series of its analogues were synthesized on solid phase and tested for inhibition of the human malarial parasite Plasmodium falciparum in culture. The results were compared with the influence of these agents on humoral and cellular immune responses. There was no clear correlation between the structure of the peptides, their immunosuppressive activity, and their antimalarial activity. However, the antimalarial activity of the peptides was apparently connected with the strong hydrophobic nature of CLA. Substitution of a less hydrophobic residue into the peptide chain led to a decrease in or even loss of detectable activity, although such peptides retained the immunosuppressive properties. A possible explanation is that the antimalarial effect of CLA and analogues may result from their influence on cell membranes rather than on some specific receptor such as cyclophilin. In agreement with this idea, binding of CLA to purified P. falciparum cyclophilin was not detected except at very high concentrations. Substitution of D-aromatic residues into the CLA molecule led to a decrease in immunosuppressive activity but had little effect on antimalarial activity, which for these peptides was of the same order as for CLA. We have therefore demonstrated that the cyclolinopeptides are a class of compound not previously shown to have antimalarial activity, and that in a series of analogues there was no correlation between antimalarial and immunosuppressive effects.

Cyclolinopeptides and their analogs--a new family of peptide immunosuppressants affecting the calcineurin system.

The results of the investigation of immunosuppressive activity of cyclolinopeptide A (CLA--cyclic hydrophobic nonapeptide present in the linseeds) and its analogs are discussed. The results obtained for other natural cyclic peptides showing structural similarities with CLA (antamanide, cycloamanides, hymenistatin, hymenamides) are also reviewed. It results from these investigations that the molecular mechanism of the CLA action is the same as that of cyclosporin A and FK-506 compound, i.e. it consists in formation of the complex with cyclophilin and inhibition--in this form--of the phosphatase activity of calcineurin. The results also suggest that the immunosuppressive activity of these compounds resides in their--Pro-Xxx-Phe- fragment, where Xxx is a hydrophobic (e.g. Leu, Val) or aromatic amino acid residue.

Immunosuppressory mini-regions of HLA-DP and HLA-DR.

Our previous studies showed, that the,TPQRGDVYT, QRGDVYT and RGDVYT fragments, located in the beta164-172 loop of HLA-DQ, strongly suppress the humoral and cellular immune response, while their shorter analogs, RGDV, RGDVY, and QRGDVY, show only weak stimulatory activity in respect to humoral immunological response. The fragments contain the RGDVY sequence that is analogous to thymopentin (pentapeptide RKDVY, an immune system activator) as well as the RGD sequence, known for its importance for cellular association phenomena. Based on the crystal structure of HLA-DR1, we also designed and synthesized a cyclic analog C*RGDVYC* (where C* indicates Cys participating in disulfide bridge) with restricted conformation, which strongly suppresses both humoral and cellular immune response. In the present study we synthesized and tested the immunological properties of the linear and cyclic HLA-DP and HLA-DR counterparts of all the above HLA-DQ fragments. Although the results show that the linear HLA-DP fragments possess moderate immunosuppressory potency, their conformationally restricted analog, C*QGDVYC*C shows a considerable suppression of both humoral and cellular immune response. The nonapeptide fragment of HLA-DR, VPRSGEVYT and particularly its cyclic analog C*SGEVYC*, are strong suppressors of the humoral response.

Length of the peptide chain influences the immunomodulatory activity of peptides related to p53 protein.

We have shown that the thymopoietin-like octapeptides derived from DNA-binding domain of p53 protein and of its mutated forms differ in their immunomodulatory properties. A strong increase of immunostimulative activity was observed for GMNRSPIL (mutated protein) in comparison with GMNRRPIL (wild-type of p53 protein) peptide. Here the elongated sequences of respective protein fragments were synthesized and investigated by plaque forming cells and delayed type hypersensitivity tests. The change of immunomodulatory activity toward immunosuppression was observed: NSSC(Acm)MGGMNRRPILTIITLE (1, wild-type) was inactive in both tests, and the C(Acm)MGGMNRSPILTIITLE (II) and YMC(Acm)NSSC(Acm)MGGMNRSPILTIITLE (III) (mutated p53 protein fragments) peptides produced immunosuppression in plaque forming cells as well as in delayed type hypersensitivity tests.

Tuftsin: on the 30-year anniversary of Victor Najjar's discovery.

After a short description of the results of Victor Najjar's research on tuftsin and of the discoveries done by other authors in the early stage of tuftsin investigation, the current state of work on tuftsin is presented, based mainly on the literature published in the years 1984-1997. The presentation follows this order: the occurrence of tuftsin and retro-tuftsin sequences in proteins, their synthesis and biology, the antigenic properties of tuftsin, its influence on phagocytic cells, and other biologic activities of tuftsin, including antimicrobial, antiviral, antitumor and central effects, and the search for tuftsin superactive analogs.

Peptides related to FKBP 39-45 loop possess immunostimulative potency.

Taking into account the sequential homology existing between thymopoietin II, the DNA-binding domain of p53 protein and FKBP (FK-506 binding protein), a series of fragments of human and bovine FKBP containing a fragment Ser39-Pro45 were synthesized. In the humoral in vitro test all the peptides act as stimulators. Whereas in the in vivo test peptides derived from bovine FKBP show an immunostimulative and those from human FKBP an immunosuppressive activity. However, after blocking the Asp residue by a Bzl group the peptide V appears to be an immunostimulator. The data obtained suggest that these peptides can influence the immune system by blocking the FKBP receptor.

Anti-IL-1 activity of peptide fragments of IL-1 family proteins.

A series of peptides containing retro-tuftsin- and tuftsin-like motifs from IL-1 proteins inhibits IL-1-induced IL-2 production and reduces the humoral immune response, thus supporting our hypothesis that tuftsin (Thr-Lys-Pro-Arg)-IL-1 competition depends on the presence of such motifs in IL-1 proteins. Some other peptides from regions of IL-1 responsible for receptor binding were also active, with peptide Ile-Thr-Gly-Ser-Glu (III) from IL-1alpha (residues 98-102), not only strongly affecting IL-2 production, but also suppressing the immune response; the analogue of hexapeptide Val-Thr-Lys-Phe-Tyr-Phe from the C-terminal part of IL-lra, with Lys replaced by Asp, was as efficient as Val-Thr-Lys-Phe-Tyr-Phe with respect to IL-1 competition.

Cyclolinopeptide A (CLA) mediates its immunosuppressive activity through cyclophilin-dependent calcineurin inactivation.

The immunosuppressive cyclic nonapeptide cyclolinopeptide A inhibits calcium-dependent, but not calcium-independent, activation of T lymphocytes comparably to the actions of cyclosporin A and FK506. The concentration required for complete inhibition, however, is 10 times higher than that of cyclosporin A. In addition, we demonstrate that calcineurin, a phosphatase which plays an important role in T lymphocyte signalling, is inhibited in vitro by cyclolinopeptide A by a mechanism dependent on the peptidyl-prolyl cis-trans isomerase (PPIase) cyclophilin A but not FKBP12. Direct binding of cyclolinopeptide A to cyclophilin A was confirmed using tryptophan fluorescence studies and PPIase assays. These results represent a third example of the production of a natural product that neutralises calcineurin by a mechanism dependent on the primary binding to a PPIase.

Sulfonated analogues of cyclolinopeptide A. Synthesis, immunosuppressive activity and CD studies.

Linear and cyclic analogues of cyclolinopeptide A (CLA) in which one or both phenylalanine residues in fragment Pro6-Pro7-Phe8-Phe9 were substituted by their sulfonated derivatives have been synthesized by SPPS method and cyclization with the BOP reagent. The peptides were examined for their immunosuppressive activity in the humoral and cellular immune response by PFC and DTH tests. All of the analogues retain some immunosuppressive activity of native CLA. Their CD spectra confirm that the optical activity of aromatic residues in CLA depends on their position in the peptide chain. Only the residue in position 8 seems to be optically active. CD spectrum of the cyclic analogue modified in position 9 is very similar to that of native CLA which correlates with its high biological activity. The chiroptical properties of the p-sulfonated Phe-residue are established.

A hexapeptide VTKFYF from C-terminal part of interleukin-1 receptor antagonist, an inhibitor of IL-1-IL-1 receptor interaction.

In order to find the low-molecular-weight interleukin-1 (IL-1) inhibitors we synthesized a series of peptides, derived from three regions of interleukin-1 receptor antagonist (IL-1ra): N-terminal (residues 5-9), central (90-98) and C-terminal (143-148). The decision was based on the thorough analysis of structural and functional properties of IL-1 proteins and the resemblance of some fragments of IL-1ra to well-known immunomodulators, like thymopentin and tuftsin. The competition between our peptides and IL-1 was measured as the inhibition of IL-1 induced IL-2 production in LBRM/CTLL cell line system. The activity of tuftsin (TKPR), a peptide immunomodulator derived from IgG molecule, was also examined. All peptides presented some activity, although the most interesting results (when the range of activity and dose-dependence were taken into account) were obtained for tuftsin and peptide VTKFYF from the C-terminal part of IL-1ra, which is in agreement with the latest reports on the structure of IL-1ra-receptor complex.

Further investigations on thymopentin-like fragments of HLA-DQ and their analogs.

Recently we showed that the fragments of HLA-DQ with the Thr-Pro-Gln-Arg-Gly-Asp-Val-Tyr-Thr and Gln-Arg-Gly-Asp-Val-Tyr-Thr sequences strongly suppress the immune response, while their shorter analogs, Arg-Gly-Asp-Val, Arg-Gly-Asp-Val-Tyr and Gln-Arg-Gly-Asp-Val-Tyr, show very weak stimulatory activity with respect to humoral immunological response. The fragments contain the sequence which is very similar to thymopentin (pentapeptide Arg-Lys-Asp-Val-Tyr, an active fragment (32-36) of thymopoietin, an immune system activator produced in thymi), and at the same time contains the Arg-Gly-Asp (RGD) sequence, known as an inhibitor of adhesion processes. In the present study we found that a hexapeptide: Arg-Gly-Asp-Val-Tyr-Thr is the smallest size fragment of HLA-DQ having both cellular and humoral immunosuppressive activity. We also found that linear and cyclic fragments of HLA-DQ do not affect cell line production of various cytokines, what suggests that the mechanism of interactions of these peptides with the immunological system is different as compared with most other known immunosuppressors.

The determination of thymopoietin conformation based on X-ray structure of a discontinuous thymopoietin-like motif of G-actin.

The biologically active conformation of thymopoietin, based on X-ray data reported for discontinuous thymopoietin-like motif of G-actin, is proposed. The conformation is compared with that resulting from the prediction made by the method of Chou & Fasman (Annu. Rev. Biochem. 47, 251-276, 1978) and Rost & Sander (Methods Enzymol. 266, 525-539, 1996).