Suppression of epimerization by cupric (II) salts in peptide synthesis using free amino acids as amino components.

An epimerization-free system for coupling N-protected peptides with free amino acids was developed. A number of inorganic substances were tested as epimerization suppressant additives during the coupling by various methods (carbodiimide plus additives, uronium salts, Woodward's reagent-K, isobutyl-chloroformate, etc.). Some of them (ZnCl2, RbClO4, LiCl, SnCl4, AlCl3, etc.) in combination with some coupling methods can guarantee coupling with minimal epimerization (D-epimer < 1%). But only a simultaneous use of 1-hydroxybenzotriazole and Cu2+ ions as additives in carbodiimide-mediated peptide couplings appeared to give a standard result (D-epimer < 0.1%). There was no epimerization even in the case when N-methyl amino acid (sarcosine) was used as an amino component, while in the absence of Cu2+ ions an unacceptable level of epimerization was observed (D-epimer, 22% for carbodiimide with the 1-hydroxybenzotriazole method). So far it has been considered that Cu2+ ions prevent obtaining peptides in high yields (< 90%) by various coupling methods. We have found that the use of 1-hydroxybenzotriazole, CuCl2 and 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide instead of dicyclohexylcarbodiimide provides a possible method for obtaining the desired peptides in 90-99% yields without epimerization. All these results were shown by employing several model peptide couplings with free amino acids as amino components dissolved in an effective solvent system which readily dissolved them.

Papain catalyzed synthesis of glyceryl esters of N-protected amino acids and peptides for the use in trypsin catalyzed peptide synthesis.

Papain catalyzed synthesis of glyceryl esters of BOC(Z)-protected amino acids and peptides was performed at 40-50 degrees C in a 50 molar excess of glycerol. Equilibrium was achieved in 6-7 h. The maximal yield of esters (50-70%) was obtained at 10% of water and pH 3.2-3.4. A lower water concentration resulted in a sharp decrease of the ester yield. The synthesized glyceryl esters of neutral amino acids are good substrates for trypsin and can be used for peptide synthesis catalyzed for trypsin. Glycerol esters are also good substrates for other enzymes possessing esterase activity.

Size-exclusion chromatography of protected synthetic polypeptide tandems in an organic solvent.

A novel method for analytical and preparative size exclusion chromatography of large water-insoluble protected peptides in an organic solvent was developed. This method was applied to analysis and separation of protected synthetic peptide tandem repeats and to a control of the reaction of peptide fragment coupling. Columns containing Toyopearl HW-40, HW-50; HW-55 and HW-60 gels of Fine grade were used, and the selectivity of each sorbent, as well as the chromatographic behaviour of the peptides on them, were examined. Separation ranges of these gels applied to separation of protected peptides in DMF were shown to be much smaller (ca. 400-14,000 Da) than those of the same gels applied to protein separations in water buffers (100-1,000,000 Da). An initial evaluation of efficiency of Toyopearl HW Superfine grade gels with respect to similar separations was performed.

An effective organic solvent system for the dissolution of amino acids.

Dimethylformamide containing strong acids (CF3 COOH, HBF4, TosOH, etc.) and an excess of tertiary base with pK < or = 6 is an effective solvent system for the dissolution of amino acids and their derivatives. The preferable base is pyridine, which forms a system with an apparent pH of 5.3. Amino acids dissolved in this solvent system readily interact with acylating reagents (BOC(2)O, ZOSu, Fmoc-OSu and activated derivatives of N-protected amino acids). A number of BOC-, Z-, Fmoc-amino acids, as well as several dipeptides, were synthesized using this solvent system with 80-99% yields.

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).

Interactions of (Ala*Ala*Lys*Pro)n and (Lys*Lys*Ser*Pro)n with DNA. Proposed coiled-coil structure of AlgR3 and AlgP from Pseudomonas aeruginosa.

The proteins, AlgR3 and AlgP, are involved in the regulation of alginate synthesis in Pseudomonas. They contain multiple repeats of Ala*Ala*Lys*Pro as do several other proteins that resemble histones. The interactions of synthesis oligopeptides composed of repeated Ala*Ala*Lys*Pro or Lys*Lys*Ser*Pro units with DNA were studied by fluorescence of the Fmoc (9-fluorenylmethyloxycarbonyl) group attached to the N-termini of the peptides. DNA quenching of the Fmoc fluorescence of the peptides was used to estimate the apparent association constants for the interaction of Fmoc(AAKP)nOH (n = 2, 4, 8, 18, 32) and of Fmoc (KKSP)nOH (n = 2, 4, 8, 16, 20, 32) with DNA. The Fmoc(AAKP)nOH peptides bind to DNA only at low ionic strength; the Fmoc(KKSP)n OH peptides interact with DNA at both low (0.05 M KCl) and high (0.2 M KCl) salt. At low ionic strength an increase in the number of the repeat units causes an increase in the apparent association constant up to approximately 2 x 10(6) M-1 for both types of peptides at N congruent to 24. The insertion of an AAKTA unit into the middle of the Fmoc(AAKP)8OH peptide increases its affinity to DNA. We propose a model of (AAKP)n and of its interaction with DNA. The repeat unit consists of a single turn of alpha-helix followed by a bend necessitated by Pro. The resultant coiled-coil forms a right-handed superhelix with 10 AAKPs per repeat distance of approximately 33 A.(ABSTRACT TRUNCATED AT 250 WORDS)

Kinetics of peptide synthesis studied by fluorescence of fluorophenyl esters.

The kinetics of the reaction of Boc-alanine-trifluorophenyl, Boc-alanine-tetrafluorophenyl, Boc-alanine-pentafluorophenyl, and Boc-alanine-p-chlorotetrafluorophenyl esters (BocAlaOTrf, BocAlaOTfp, BocAlaOPfp, and BocAlaTfc, respectively) with leucine amide and with valine methyl ester have been measured using changes in fluorophenyl chromophore emission at 375 nm. The kinetic data cannot be well fit with a simple second-order reaction scheme. Measurements of the reaction kinetics at different concentrations of the reagents showed that the expression for the reaction rate is V = kC(N)0.5C(AE)1.5, in which k is the reaction rate constant, CN is the concentration of either LeuNH2 or ValOCH3, and CAE is the concentration of the fluorophenyl ester. This reaction equation indicates a complex, probably chain-like, reaction mechanism. The order of reactivity for these active esters with ValOCH3 is BocAlaOTfc > BocAlaOPfp > BocAlaOTfp > BocAlaTrf. The apparent rate constant, k, for the reaction with LeuNH2 is higher than that for the reaction with ValOCH3.

p-Chlorotetrafluorophenyl esters of N-protected amino acids.

p-Chlorotetrafluorophenyl (Tfc) esters of protected amino acids and peptides are more reactive than are the well known pentafluorophenyl (Pfp) esters. Two reagents, p-chlorotetrafluorophenyltrifluoroacetate (Tfc-OTfa) and di-(p-chlorotetrafluorophenyl)carbonate (di-Tfc-carbonate), can be used for their syntheses, thereby avoiding use of the allergic dicyclohexylcarbodiimide. This is especially important for bulk preparations. Many Fmoc- and Boc-amino acid-OTfc esters have been synthesized and characterized. The hexadecameric tandem repeat H-(AlaAlaLysPro)4-OH was synthesized using di-Tfc-carbonate for the preparation of Tfc-esters.

Synthesis and properties of the peptide corresponding to the ACTH-like sequence of human immunoglobulin G1.

The decapeptide Val-Lys-Lys-Pro-Gly--Ser-Ser-Val-Lys-Val (termed immunocorticotropin) corresponding to the sequence 11-20 of the variable part of the human immunoglobulin G1 heavy chain was synthesized. The ACTH-like peptide was found to have an ability to increase body temperature. Intracerebroventricular injection of 5-10 micrograms of the peptide to rabbits induced an elevation of body temperature by 0.7-1.3 degrees C. The ACTH-like peptide was shown to compete with [125I]-ACTH (13-24) for binding to receptors on murine brain synaptic membranes and to activate adenylate cyclase of these membranes.

Protease-catalyzed peptide synthesis using inverse substrates: the synthesis of Pro-Xaa-bonds by trypsin.

Benzyloxycarbonyl-L-proline p-guanidinophenyl ester is an "inverse substrate" for trypsin; i.e., the cationic center is included in the leaving group instead of being in the acyl moiety. This substrate can be used in trypsin-catalyzed acyl-transfer reactions leading to the synthesis of Pro-Xaa peptide bonds. The reaction proceeds about 20 times slower than reaction with similar alanine-containing substrates, but the ratio between synthesis and hydrolysis is more favorable. The investigation of a series of nucleophiles led to information about the specificity of the process. Nucleophiles differing only in the P(1)'-position show an increasing acyl transfer efficiency in the order Phe < Gly < Ley < Ser < Ala < lle. C terminal elongation of the nucleophiles is of minor influence on their efficiency. The formation of an H bond between the acyl-enzyme and the nucleophile seems to play an important role in the aminolysis of the acyl-enzyme.

Protease-catalyzed peptide synthesis using inverse substrates: the influence of reaction conditions on the trypsin acyl transfer efficiency.

Benzyloxycarbonyl-L-alanine p-guanidinophenyl ester behaves as a trypsin "inverse substrate," i.e., a cationic center is included in the leaving group instead of being in the acyl moiety. Using this substrate as an acyl donor, trypsin catalyzes the synthesis of peptide bonds that cannot be split by this enzyme. An optimal acyl transfer efficiency was achieved between pH 8 and 9 at 30 degrees C.The addition of as much as 50% cosolvent was shown to be of minor influence on the acyl transfer efficiency, whereas the reaction velocity decreases by more than one order of magnitude. The efficiency of H-Leu-NH(2) and H-Val-NH(2) in deacylation is almost the same for "inverse" and normal type substrates.

Noncovalent complex between domain AB and domains CD*EF of parvalbumin.

The interaction between domain AB and domains CD*EF of pike parvalbumin III has been studied by intrinsic fluorescence spectroscopy. In the presence of Ca2+ ions, parvalbumin fragment 38-108 containing two calcium binding sites interacts with the short peptide 1-37 with association constant 10(5.3 +/- 0.5) M-1. Removal of Ca2+ ions results in the disappearance of the interaction. The affinity of the complex of the two fragments for calcium is 50-times higher than the affinity of the isolated fragment 38-108, but slightly lower than that of the intact protein.

Characterization of the S'-subsite specificity of bovine pancreatic alpha-chymotrypsin via acyl transfer to added nucleophiles.

The S'-subsite specificity of bovine pancreatic alpha-chymotrypsin was investigated by acyl transfer reactions using a series of amino-acid- and peptide-derived nucleophiles. The nucleophilic efficiency covers a range of more than three orders of magnitude, reflecting the specificity of the acyl transfer process. Positively charged H-Arg-NH2 was the most efficient nucleophile of the series while peptides with free carboxyl groups show poor nucleophilic behaviour. This is explained by electrostatic interactions with the residues Asp35 and Asp64 of the enzyme. These negatively charged groups, which are localized near the appropriate S' binding sites, repel carboxylate groups of the nucleophiles. There is a good correlation between the nucleophile efficiencies found for different acyl enzymes. An investigation of a series of 14 water-soluble acyl donor esters, differing both in the P1 residue and in the number of amino acids, revealed that the nature of the acyl group affected the acyl-enzyme partitioning between water and added nucleophile in the range of one order of magnitude.

Characterization of the S'-subsite specificity of porcine pancreatic elastase.

A number of maleyl peptide p-nitrobenzyl esters have been synthesized to study elastase-catalyzed hydrolysis reactions. These new substrates were used as acyl donors to investigate the S'-subsite specificity of porcine pancreatic elastase by partitioning of the acyl enzyme between various added nucleophiles and water. The following results were obtained. 1. Porcine pancreatic elastase prefers amino acid residues with small side chains in the P'1 position. 2. The nucleophile binding is improved by a positively charged P'1 side chain, whereas a negatively charged function results in a very low binding tendency. 3. Elongation of the nucleophile to the P'2 position leads to higher aminolysis rates. 4. S' specificity is substantially influenced by the P1 residue of the acyl enzyme.

An apparatus for continuous analysis of protease-catalyzed acyl transfer reactions.

An apparatus that allows continuous analysis of protease-catalyzed acyl transfer reactions is described. Hydrolysis reaction is assayed using automatic titration. A continuous determination of amino group concentration by reaction with o-phthalaldehyde gives the rate of peptide bond formation. The apparatus allows the determination of the partition constant for the nucleophile at various nucleophile concentrations from one run.

Binding of calcium by fragment 38-108 of pike parvalbumin.

Cyanogen bromide splitting of pike parvalbumin III was carried out and fragment 38-108 containing two calcium-binding domains was isolated. The obtained fragment binds calcium rather well (Kd = 1.6.10(-5) M), possesses a secondary structure, its CD spectrum changes after removal of calcium.