Polypeptides. XV. The synthesis and oxidation of some L-cysteinylpolyglycyl-L-cysteines

Single Proline Residues can Dictate the Oxidative Folding Pathways of Cysteine-rich Peptides

The cysteine-rich N and C-terminal domains of minicollagen-1 from Hydra nematocysts fold with excesses of oxidized/reduced glutathione (10:1) into globular structures with distinct cystine frameworks despite their identical cysteine sequence pattern. An additional main difference is the cis conformation of a conserved proline residue in the N-terminal and the trans conformation of this residue in the C-terminal domain. Comparative analysis of the oxidative folding revealed for the C-terminal domain a fast and highly cooperative formation of a single disulfide isomer. Conversely, oxidation of the N-terminal domain proceeds mainly via an intermediate that results from the fast quasi-stochastic disulfide formation according to the proximity rule. The rate of conversion of the bead-like isomer into the globular end-product is largely dominated by the trans-to-cis isomerization of the critical proline residue as well assessed by its replacement with (4R)- and (4S)-fluoroproline known to exhibit distinct propensities for the trans and cis conformation, respectively. Independently, whether the trans or cis conformation is favored by these substitutions, both analogues retain sufficient sequence-encoded information to fold almost quantitatively into the identical cystine framework and thus spatial structure of the parent peptide with the critical proline residue as cis isomer, but at rates significantly lower for the (4R) than for the (4S)-fluoroproline analogue. Correspondingly, other sequence-encoded structural elements have to act as a driving force for these unidirectional folding pathways despite the rather simple sequence composition consisting only of aliphatic residues, some proline and only one aromatic residue (tyrosine) in the core parts of the C and N-terminal domains. The two cysteine-rich domains of minicollagen-1 may well represent ideal targets for ab initio structure calculations in order to learn more about the elementary information encoded in such primordial molecules.

NMR evidence of formation of cyclocystine loops in peptide models of the high sulfur proteins from wool

We report that in peptide models of the high sulfur proteins of the matrix from wool a disulfide bond forms between two sequential Cys-residues as a result of a simple oxidation procedure. This tiny cyclocystine loop manifests itself in many ways in 1H NMR spectra. The formation of the loop is accompanied, as expected, by conversion of the Cys-Cys peptide bond from its usual trans-configuration into the energetically less favorable cis-configuration. Possible consequences of the formation of cyclocystine loops for the elasticity of the network of the matrix are discussed.

Use of local electrostatic environments of cysteines to enhance formation of a desired species in a reversible disulfide exchange reaction

The role of electrostatic factors has been evaluated for the reversible disulfide exchange reaction between N-acetylcysteine (A) and a peptide fragment (B) comprising residues 85-114 of Kunitz soybean trypsin inhibitor. In A, the sulfhydryl group has a negative carboxyl neighbor on the cysteine itself. In B, the only charged group within five residues of the single cysteine at position 86 is the positive N-terminal amino group on residue 85. The concentrations of the monomers A and B and of the disulfides AA, AB and BB have been determined as a function of time in kinetic experiments at pH 7, 23 degrees C and ionic strengths of 20 mM and 1 M. At both ionic strengths the sulfhydryl acid dissociation constants Ka have been determined for A and B, as well as the four rate constants for the disulfide exchange reaction. The electrostatic effects are small in magnitude but occur in expected directions. Local cysteine environments enhance formation of the mixed disulfide (AB), having a favorable configuration of adjacent unlike charges and generate decreases in the AA and BB disulfides joining regions of identical charge. These experiments represent an initial step towards use of intrinsic protein functional groups to direct formation of specific disulfides in a synthetic protein.

Antibodies against a synthetic peptide of the avian retrovirus pp32 protein and the beta DNA polymerase subunit

Antibodies directed against a synthetic peptide (14 amino acids in length), whose amino acid sequence was predicted from the nucleotide sequence of the polymerase gene of Rous sarcoma virus (RSV), specifically immunoprecipitated the RSV beta polymerase subunit and the pp32 protein but not the alpha polymerase subunit. The first amino acid of the synthetic peptide is located approximately 30,800 Da from the predicted carboxyl terminus of the polymerase gene. These studies confirm the correct reading frame predicted for the polymerase gene and establish a minimal NH2 terminus for the pp32 DNA binding protein, which was previously shown to be derived from the carboxyl terminus of the polymerase gene.

Oxidative folding of cystine-rich peptides vs regioselective cysteine pairing strategies

The methodology of regioselective cysteine pairings in synthetic multiple-cystine peptides has progressed in the past years to an efficiency that allows for at least three specific inter- and intrachain disulfide bridgings. Conformational studies on various multiple-cystine peptides like hormones, protease inhibitors, and toxins revealed that these bioactive peptides, generated by posttranslational processing of precursor proteins, are folded into miniprotein-like compact globular structures of remarkable stability. This strongly suggests protein domain or subdomain properties of these families of peptides, and thus sufficient sequence-encoded information for correct oxidative refolding under appropriate experimental conditions. From intensive research on the mechanisms and pathways of oxidative refolding of proteins in vivo and in vitro, the efficient methods have emerged for simulating nature in the regeneration of native folds not only for intact proteins, but also for protein domains and subdomains. In fact, the results obtained in the oxidative folding of excised protein fragments and of relatively low mass products of posttranslational processings show that this procedure is indeed a simple way of preparing peptides with several disulfide bonds, if optimization of reaction conditions is performed in terms of redox buffer, temperature, and additives capable of disrupting aggregates and of stabilizing nascent secondary structures. Moreover, with increased knowledge about stable, small natural cystine frameworks, their use instead of artificial templates should facilitate engineering of synthetic miniproteins with specific conformation and tailored functions.