Biomedical subjects

E Panou-Pomonis

Publications and source records attributed to E Panou-Pomonis.

10 recordsLinked to original sources

PubMed2001

A diepitopic sequential oligopeptide carrier (SOCn) as mimic of the sm autoantigen: synthesis, conformation and biological assays.

Anti-Sm (Sm: U1-U6 RNA-protein complex) antibodies are usually considered highly specific for systemic lupus erythematosus (SLE), while anti-U1RNP (U1RNP: U1RNA-protein complex) are thought of as diagnostic criteria for the mixed connective tissue disease (MCTD). However, both antibody specificities coexist in SLE and MCTD, in varying percentages. Although the anti-Sm/anti-U1RNP immunological cross-reactivity has been initially attributed to a common motif, PPXY(Z)PP (where X, Y, Z are various amino acids), found in the Sm, U1-A and U1-C autoantigens, it appears that the conformational features of the Sm epitopes also play an important role in the immunoreactivity. The PPGMRPP and PPGIRGP main epitopes of the Sm antigen were coupled in duplicate to the tetrameric Ac-(Lys-Aib-Gly)4-OH, SOC4, carrier to form the [(PPGMRPP)2, (PPGIRGP)2]-SOC4 construct as a mimic of the native Sm. It was found that: (i) the 3(10) helical structure of SOC4 allows the epitopes to adopt an exposed orientation, similar to their free forms, that facilitates their recognition from the anti-Sm antibodies, and (ii) the U1-RNP cross-reactivity is minimized.

Amino Acids↗

PubMed2000

Arg side-chain-backbone interactions evidenced in model peptides by 17O-NMR spectroscopy.

The guanidinium group of arginine possesses a variety of biochemical functions, either by participating in direct interactions in recognition processes, or by stabilizing secondary structures. Three model compounds, selectively (17)O enriched, Ac-Arg-Ala-[(17)O]Pro-NH(2) (1), Piv-Arg-Pro-[(17)O]Gly-NH(2) (2) (C-terminal segment of the luteinizing hormone releasing hormone), and Piv-Nle-Pro-[(17)O]Gly-NH(2) (3), were prepared and studied by (17)O-nmr spectroscopy. A direct hydrogen-bonded interaction between the Arg side chain and the carbonyl main chain carboxy-terminus was found, thus confirming the tendency of Arg to participate in proton-acceptor functions.

Arginine↗

PubMed2000

The clinical relevance of antibodies to ribosomal-P common epitope in two targeted systemic lupus erythematosus populations: a large cohort of consecutive patients and patients with active central nervous system disease.

OBJECTIVES: To develop an enzyme linked immunosorbent assay (ELISA) using as substrate a synthetic 22-aminoacid peptide, corresponding to the ribosomal P0, P1 and P2 common epitope. To study the specificity and sensitivity of the method and evaluate the frequency and clinical associations of anti-P antibodies in two groups of systemic lupus erythematosus (SLE) patients: (a) unselected SLE patients and (b) SLE patients with central nervous system (CNS) involvement. PATIENTS AND METHODS: The C-terminal 22 aminoacid peptide of the ribosomal P proteins (Lys-Lys-Glu-Glu-Lys-Lys-Glu-Glu-Lys-Ser-Glu-Glu-Glu-Asp-Glu-Asp-Met- Gly-Phe-Gly-Leu-Phe-Asp) was synthesised according to Merrifield's solid phase procedure. Purification of the peptide was performed by preparative high performance liquid chromatography and confirmed by amino acid analysis. Using this peptide, in a concentration 5 microg/ml, an ELISA was developed. The presence of anti-P antibodies was evaluated by western blot using purified ribosomal proteins from rat liver. Sera from 178 consecutive patients with SLE and 28 patients with SLE and CNS manifestations were tested. Sera from 58 patients with rheumatoid arthritis and 57 patients with primary Sjögren's syndrome were used as controls. The cut off point of the assay was defined using 124 normal sera. RESULTS: The specificity of the assay was evaluated by homologous inhibition. Pretreatment of positive sera with soluble 22mer peptide of the ribosomal P proteins resulted in 88% inhibition. The concordance between the peptide assay and western blot was found to be 83%. Thirty three of 178 (18. 6%) of the unselected SLE patients had antibodies to P-protein common epitope. Their presence was associated with more active disease (European Consensus Lupus Activity Measurement, ECLAM scoring system) (p<0.001), higher levels of anti-ds DNA antibodies (p<0.05) and lower levels of the C4 component of complement (p<0.01). Eleven of 28 (39.3%) patients with SLE and active CNS involvement had antibodies to P-protein. The overall prevalence of anti-P antibodies in active CNS disease patients was statistically significantly higher, as compared with unselected SLE patients (chi(2)=6.04, p<0.05). These antibodies were found in a high proportion of patients without anticardiolipin antibodies (52.4%) and they were associated with diffuse CNS involvement (psychiatric disorders (71%) and epilepsy (75%)). CONCLUSIONS: A synthetic analogue of the common epitope of ribosomal P-proteins can be use as an antigen for the detection of anti-P antibodies. These antibodies are associated with active SLE and CNS involvement particularly in patients without anticardiolipin antibodies.

Adult↗

PubMed2000

B-Cell epitope mapping of DNA topoisomerase I defines epitopes strongly associated with pulmonary fibrosis in systemic sclerosis.

We hypothesized that B-cell epitope mapping of DNA Topoisomerase I (type-I topoisomerase, or Topo I) may define epitopes strongly associated with pulmonary interstitial fibrosis (PIF) in systemic sclerosis (SSc). B-cell epitope mapping of Topo I was performed using 63 20-mer peptides overlapping by eight residues and spanning the entire length of the Topo I sequence. These peptides, coupled to polystyrene pins, were tested for antibody binding by enzyme-linked immunosorbent assays (ELISAs) using immunoglobulin G fractions from anti-Topo I, anticentromere, anti-U3RNP-positive, and normal sera. Four major epitopes were recognized by anti-Topo I sera, but not from the control sera: WWEEERYPEGIKWKFLEHKG (205-224, epitope I), RIANFKIEPPGLFRGRGNHP (349-368, epitope II), PGHKWKEVRHDNKVTWLVSW (397-416, epitope III), and ELDGQEYVVEFDFLGKDSIR (517-536, epitope IV). Peptide-epitopes were then synthesized in their soluble forms and ELISA systems were developed. Epitopes II to IV are localized at highly exposed sites of the Topo I tertiary structure, whereas epitope I is localized at a less accessible site. In a cohort of 81 patients with SSc with clinical data on the evolution of their disease, patients with antibodies in their sera recognizing at least three of the four epitopes had 3.1 times (P = 0.02) the hazard of developing PIF compared with patients whose sera recognized no epitopes or only one or two of the four epitopes. The discrimination was much stronger than that achieved by the simple determination of Topo I antibodies by counterimmunoelectrophoresis and immunoblot (hazard ratio 1.7, P = 0.30) in the same patients. B-cell epitope mapping of the anti-Topo I response has identified four major epitopes which cumulatively show a strong association with the development of PIF in SSc.

Amino Acid Sequence↗

PubMed1996

Immunoreactivity and conformation of the P-P-G-M-R-P-P repetitive epitope of the Sm autoantigen.

Anti-Sm antibodies are usually considered highly specific for systemic lupus erythematosus (SLE), while anti-U1 RNP antibodies are found in high titers in patients with mixed connective tissue disease (MCTD). The sequence P1-P-G-M-R-P-P7, present in three copies in the Sm (U1-U6 RNA-protein complex) autoantigen, is an important functional domain of the antigenic determinants. The immunoreactivity of this proline-rich repetitive epitope was investigated by testing sera with various autoantibody specificities for reactivity against this epitope, as well as its conformational properties by means of 1D and 2D 1HNMR spectroscopy. It was found that the P-P-G-M-R-P-P epitope is recognized mainly by anti-U1RNP and/or anti-Sm positive sera, but also by anti-Ro(SSA) (hY1RNA-protein complex) and anti-La(SSB) (hY1RNA-protein complex) positive sera, although these sera are negative for anti-U1RNP and anti-Sm. Conformational analysis of the proline-rich epitope in DMSO-d6 solution obtained from lyophilized aqueous solution at pH 5 showed the presence of at least three conformers. The main conformer A (62%) is stabilized by an ionic interaction between the guanidinium and the C-terminal carboxylate groups, and the Pro6-Pro7 peptide bond adopts the cis form. A type II beta-turn is also present in the N-terminal sequence (Pro1-Pro-Gly-Met4-) of this conformer. Conformer B (21%) is also stabilized by a similar ionic interaction, as in conformer A, while the NMR data indicate the absence of a folded structure in the N-terminal tetrapeptide of this conformer. Conformer C (17%) adopts a completely extended structure. The multiple conformers of the P-P-G-M-R-P-P may offer some explanation for the reactivity of sera with various autoantibody specificities against this epitope.

Amino Acid Sequence↗

PubMed1991

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.

Amino Acid Sequence↗

PubMed1991

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.

Amino Acid Sequence↗

PubMed1986

Circular dichroism studies on chromatin models. Interactions between DNA and sequential polypeptides containing arginine.

The sequential polypeptides (L-Arg-Xaa-Gly)n where Xaa represents amino acid residues Ala, Val and Leu, were employed as models of arginine-rich histones, in studying their interactions with nucleic acids. These polypeptide-DNA complexes were prepared using gradient dialysis and their conformational properties were investigated by circular dichroism spectroscopy. It was found that poly(L-Arg-L-Val-Gly) caused pronounced structural changes in the DNA molecule (conformational transition from B to the more compact and asymmetric C form) as a function of ionic strength and polypeptide: DNA ratio. In contrast the DNA interaction with poly (L-Arg-L-Ala-Gly) and poly (L-Arg-L-Leu-Gly) increased in the order of Ala----Leu, but with slight structural changes in the DNA secondary conformation. Thus, the importance of the composition, amino acid sequence and conformation of the polypeptides which bind to DNA was demonstrated. The significance of the hydrophobic forces besides the arginine-phosphate charge interaction, which modulate the nature of the polypeptide-DNA complexes and their condensation into higher-ordered tertiary structures, as found in chromatin, was also confirmed.

Amino Acid Sequence↗

PubMedDate not supplied

A three-residue cyclic scaffold of non-RGD containing peptide analogues as platelet aggregation inhibitors: design, synthesis, and structure--function relationships.

Antagonists of fibrinogen at the GPIIb/IIIa receptor, which is the most abundant membrane protein on the platelet surface, are under active investigation as potential antithrombotics. The critical interaction between GPIIb/IIIa and fibrinogen can be inhibited by either linear or cyclic RGDS-containing peptides, which have been proved as lead compounds in the design of platelet aggregation inhibitors. In this study we present the design and construction of a new class of cyclic (S,S) non-RGD containing peptide sequences, using two Cys as a structural scaffold for the development of antiaggregatory agents. The (S,S)-CDC- sequence was incorporated as a conformational constraint, in molecules bearing at least one positive charge with the general formula (S,S)XCDCZ, where X = Ac-Arg, Pro-Arg, Pro-Ser-Lys, and Pro-Ser-Arg, and Z = -NH(2) and Arg-NH(2). Investigation of the structure-function relationships was performed on the basis of (a) the local conformation induced by the (S,S)-CDC motif, (b) the distance of the positively (R-C(zeta) or K-N(zeta)) and negatively (D-C(gamma)) charged centers, (c) the presence of a second positive or negative charge on the molecule, and (d) the orientation of the basic and acidic side chains defined by the pseudo dihedral angle (Pdo), which is formed by the R-C(zeta), R-C(alpha), D-C(alpha), and D-C(gamma) atoms in the case of (S,S)-RCDC and by the K-N(zeta), K-C(alpha), D-C(alpha), and D-C(gamma) atoms in the case of (S,S)-KCDC.

Amino Acid Sequence↗

PubMedDate not supplied

1H-NMR studies on arginine tripeptides: evidence for guanidinium-C-terminal carboxylate interactions.

Guanidinium-C-terminal carboxylate interactions are involved in the establishment of the secondary structure of various biologically active peptide sequences. The conformational properties of a series of arginine-containing tripeptides, L-Arg-X-Gly (X = L-Ala, Val, Leu), in DMSO solutions at physiological pH, have been studied by means of 1D and 2D 1H-NMR spectroscopy. Measurements of the chemical shifts, NOE effects and temperature coefficients showed that the ArgN epsilon H and ArgN eta H2 groups form two hydrogen bonds with the C-terminal carboxylate moiety, whereas the ArgN alpha-terminal nitrogen is in the amino state. Our results point out the significant contribution of the C-terminal carboxylate group, at physiological pH, in the stabilization of the Arg side-chain structure in peptides simultaneously containing arginine residues and carboxy terminal sequences.

Amino Acid Sequence↗