V. Tsikaris

NMR study on a SRYD-containing fibronectin-like sequence (250–257) of Leishmania gp63: contribution of residual water in the dimethyl sulfoxide solution structure

The conformational characteristics of the I250ASRYDQL257 synthetic octapeptide, which incorporates the SRYD adhesion site (252–255) of Leishmania gp63, have been investigated at pH 2 and 5, by means of 1 D and 2D 1H NMR spectroscopy (temperature coefficient values, chemical shifts, vicinal coupling constants and NOE effects). It was found that elimination of residual water from the dimethyl sulfoxide (DMSO) solution at pH 2 provides exchange peaks in the ROESY and HOHAHA spectra similar to those obtained for the DMSO peptide solution at pH 5. This common structure is stabilized (i) by the formation of a type I β-turn involving the QNH→RCO interaction and (ii) by a possible interaction between the guanidinium and the D-β-carboxylate groups. After treatment with molecular sieves, the remaining residual water is redistributed between the peptide functional groups and participates in the rigidification of the new conformational state.

Fine Structural Characterization of the Main Immunogenic Region of the Nicotinic Acetylcholine Receptor

The nicotinic acetylcholine receptor (AChR) of fish electric organs and mammalian muscle is a complex transmembrane glycoprotein formed by five homologous subunits in a stoichiometry α2βγδ, of mol. weight 290.000. The two α-subunits carry the two ACh binding sites. The complete amino acid sequence of Torpedo electric organ and mammalian muscle AChR subunits is known (reviewed in Numa et al., 1983; Changeux & Revan, 1987).

Sequential Oligopeptide Carriers (SOCn) for Producing Potent Antigens and Effective Immunogens

A new class of Sequential Oligopeptide Carriers (SOCn), namely (Lys-Aib-Gly)n (n=2–7), for anchoring antigenic/immunogenic peptides is presented. The aim of this construction was to model artificial carriers with predetermined conformation, so that the attached peptides would not interact to each other or with the carrier, and would thus retain their original active conformation. The NMR study and the molecular dynamics calculations confirmed that the SOCn adopt rigid helicoid structure comparable to a canonical 310-helix, with a somewhat curved axis. The peptides linked to the SOCn retain their original structural profile, as it was also demonstrated by the NMR study. It is concluded that the SOCn impose a favourable disposition of the anchored peptides for generating potent antigens and effective immunogens.

Conformational Properties of the Arg-Leu-Gly Tripeptide—DMSO—Water Clusters with the Combined Use of Molecular Dynamics and Energy Minimization Studies

The Arg-Leu-Gly tripeptide is the repeating fragment of sequential arginine-rich polypeptides capable of interacting with DNA. The conformational influence of solvent molecules (DMSO/H2O) were investigated with the combined use of molecular dynamics and energy minimization. It was found that water molecules greatly contribute to the peptide structure by solvating all its hydrophylic sites even in the presence of DMSO excess, whereas one water molecule links the ammonium and carboxylic ends of the Arg-Leu-Gly. The persistence of residual water, which was confirmed by varying the computer simulation parameters, indicates that pretreatment of peptide segments in aqueous solutions should greatly affect their conformational properties in organic media. A satisfactory agreement between experimental data (1H-NMR and IR spectroscopy) and the presented computational study deserves also to be noted.

Changes in the c.d. spectra of calf thymus DNA induced by sequential polypeptides in aqueous solutions Part I

Interactions of calf thymus DNA with sequential polypeptides were studied using c.d. spectroscopy in aqueous solutions. It was found that DNA structural alterations induced by sequential polypeptides (L-Arg-X-Gly)n (where X = L-Val, Leu, Ile, Nva, Nle) are modulated by the nature of the X residue. Thus, the polypeptide (L-Arg-L-Nva-Gly)n induced the 10.2B-DNA form, whereas the polypeptides (L-Arg-L-Ile-Gly)n having one methyl group less on the X residue side chain, did not provide any significant modification to the structure of DNA. The effect of ionic strength from 0.14 M NaCl (physiological value) to zero was also analysed on the basis of the observed c.d. changes and the degree of complexation in the DNA-polypeptides was estimated.

Changes in the c.d. spectra of calf thymus DNA induced by sequential polypeptides in trifluoroethanol solutions. Part II.

Interactions between calf thymus DNA and (L-Arg-X-Gly)n sequential polypeptides (where X = L-Ala, Val, Leu, Ile, Nva, Nle) in trifluoroethanol: water (40:60) solutions in the salt range of 0.12-0.5 M NaCl, were studied using c.d. spectroscopy. It was found that DNA tertiary structure (psi form) is modulated by the nature of the polypeptides (variation of X residue). The effect of the secondary structure of polypeptides on the formation of psi-DNA was also analysed. Unordered polypeptides destabilized psi aggregates, while helical polypeptides favoured DNA tertiary structure. A loss of tertiary structure was observed in the presence of the (L-Arg-L-Val-Gly)n, which can be attributed to the ability of valine to suppress psi-type DNA.