Hisztidin-gazdag fehérjék fémkötő sajátságainak modellvizsgálata oligopeptid fragmensek fémkomplexeivel = Model studies on the metal-binding properties of histidine rich proteins with metal complexes of oligopeptide fragments

A kutatási projekt célja a plazma fehérje hisztidin-gazdag glikoprotein (HRG) hisztidin-gazdag régiója (HRR) fémkötő sajátságainak jobb megismerése volt. A HRR fémionokkal való kölcsönhatása szerepet játszik a HRG számos biológiai funkciójának kifejtésében. A cél érdekében számos, a HRR tandem módon ismétlődő (G)HHPH(G) szekvenciáját tartalmazó terminális pozíciókban védett oligopeptidet, illetve azok módosított verzióit állítottuk elő és vizsgáltuk kölcsönhatásukat cink(II)- és réz(II)ionokkal. Az egymáshoz kapcsolt HHPHG egységek számával együtt nő a megköthető fémionok száma is. A két egységből felépített dekapeptidben az első fémion a monomer pentapeptidhez képest eltérő módon, nagy valószínűséggel főként a (H)HPHGH szakaszon koordinálódik. Ezt alátámasztják a módosított szekvenciájú hisztidin-prolin tartalmú peptidek cink(II)- és réz(II)komplexeinek részletes vizsgálatával nyert szerkezeti és stabilitási adatok is. Az első fémion koordinációja a dekapeptidben olyan peptid konformáció változást eredményez, mely elősegíti a második fémion felvételét, és ez extra stabilizációt eredményez. Az eredmény jelentőségét a natív HRG lépcsőzetes cink(II) megkötésében megfigyelt kooperatív hatás adja. Az Ac-HHPHG-NH2 ligandum réz(II)ionok jelenlétében, lúgos pH-tartományban, a H-P közti peptidkötés hidrolitikus hasadásával fragmenseire bomlik, ami fontos lehet annak tükrében, hogy a HRG antiangiogén/antitumor hatásának kifejtéséhez a HRR-nek ki kell szakadnia a proteinből. | The aim of the project was to better explore the metal binding properties of the histidine-rich region (HRR) of the plasma protein histidine-rich glycoprotein (HRG). The metal ion interaction of the HRR plays a role in many of the biological functions of HRG. We have synthesized several terminally protected oligopeptides, based on the tandem repeated (G)HHPH(G) sequence of the HRR, and their modified versions, and studied their interaction with zinc(II)- and copper(II). The number of metal ions able to bind to the sequences correlates with the number of connected HHPHG units. In contrast with the monomer pentapeptide, the first metal ion is likely to bind mainly at the (H)HPHGH part of the decapeptide having two HHPHG units. This is also supported by structural and stability data obtained from detailed studies on the zinc(II)- and copper(II) complexes of altered histidine-proline containing peptide sequences. The coordination of the first metal ion causes a conformational change of the decapeptide that assists the binding of the second metal ion and it results in an extra stabilization. This has an importance in view of the cooperativity observed in the stepwise zinc(II)-binding to the native HRG. The ligand Ac-HHPHG-NH2 splits into its fragments by the hydrolysis of the H-P peptide bond in the presence of copper(II) in alkaline medium, which might have a significance considering that the HRR has to be released from HRG to exert its recognized antiangiogenic/antitumor effect

Interaction Of As(III) with Thiolate-Containing Molecules

The aqueous solutions of arsenous acid with thiolate containing organic ligands such as the meso and racemic forms of 1,4-dithiol-butane-2,3-diol, (dithioerythritol – dte and dithiothreitol - dtt) as well as 2,3-dimercaptopropanol (called also British anti-Lewisite (BAL) or Dimercaprol) were investigated. pH-mertric titrations were performed in solutions with different molar ratios of As(III) and the ligands. The pKa values for As(OH)3, and the ligands determined from these data were in good agreement with the literature data. In all investigated systems containing both As(OH)3 and one of the ligands, the deprotonation steps appeared at a higher pH in the titration curves, than in those of the individual components. This unusual observation was explained by the condensation reactions between the reagents taking place in the pH < 8 range. In some of these systems the pH-metry was combined with NMR and UV spectroscopic measurements. We observed the complexes with 1:1 As(III):ligand composition as being the major species in aqueous solutions. In the case of As(III)-dte system we could crystallize the complex of 1:1 composition from ethanolic solution

Competition of zinc(II) with cadmium(II) or mercury(II) in binding to a 12-mer peptide

Speciation of the complexes of zinc(II) with a dodecapeptide (Ac-SCPGDQGSDCSI-NH2), inspired by the metal binding domain of MerR metalloregulatory proteins, have been studied by pH-potentiometric titrations, UV, SRCD (synchrotron radiation circular dichroism) and 1H NMR experiments. (MerR is a family of transcriptional regulators the archetype of which is the Hg2+-responsive transcriptional repressor-activator MerR protein.) The aim of the ligand-design was to retain the advantageous metal binding features of MerR proteins in a model peptide for the efficient capture of toxic metal ions. The peptide binds zinc(II) via two deprotonated Cys-thiol groups and one of the Asp-carboxylates in the ZnL parent complex, possessing a remarkably high stability (logK = 9.93). In spite of the relatively long peptide loop, bis-complexes are also formed with the metal ion under basic conditions. In a competition with cadmium(II) or mercury(II), zinc(II) cannot prevent the binding of toxic metal ions by the thiolate donor groups of the ligand. Around neutral pH one equivalent of mercury(II) was shown to fully replace zinc(II) from the ZnL species. Partial replacement of zinc(II) from the peptide by one equivalent of cadmium(II), relative to zinc(II) and the ligand, is also presumable, nevertheless, spectroscopic data may suggest the formation of mixed metal ion complexes, as well. Based on the obtained results the investigated dodecapeptide can be a promising candidate for capturing toxic metal ions in practical applications

Mimics of Small Ribozymes Utilizing a Supramolecular Scaffold

For elucidating the mechanism of the general acid/base catalysis of the hydrolysis of RNA phosphodiester bonds, a number of cleaving agents having two cyclen moieties tethered to a 1,3,5-triazine core have been prepared and their ability to bind and cleave UpU studied over a wide pH range. Around neutral pH, the cleaving agents form a highly stable ternary complex with UpU and ZnII through coordination of the uracil N3 and the cyclen nitrogen atoms to the ZnII ions. Under conditions where the triazine core exists in the deprotonated neutral form, hydrolysis of UpU, but not of ApA, is accelerated by approximately two orders of magnitude in the presence of the cleaving agents, suggesting general base rather than metal ion catalysis. The probable mechanism of the observed catalysis and implications to understanding the general acid/base-catalyzed phosphodiester hydrolysis by ribozymes are discussed

Increased nuchal translucency and congenital heart defects in euploid fetuses: the Szeged experience

Objective: To determine the utility of the first-trimester fetal nuchal translucency (NT) thickness in the prediction of fetal cardiac malformations. Design: Retrospective study. Setting: Department of Obstetrics and Gynecology and Medical Genetics, University of Szeged. Methods: The pre- and postnatal course and outcome. and the relationship between the first-trimester fetal NT thickness and fetal congenital heart defects (CHDs) in 4309 pregnancies ended up with birth or therapeutic abortion between January 1998 and June 2000 were registered. Prenatal care included first- and second-trimester fetal sonography at weeks 10-13 and 18-20, respectively. Results: 4251 births and 58 first- and second-trimester therapeutic abortions due to lethal congenital malformations or chromosomal abnormalities were recorded. Altogether 209 (4.9%) congenital malformations were detected, 39 (18.7%) of which were heart defects with normal karyotype. At birth, 151 congenital malformations were diagnosed. 34 of them were known prenatally. The prevalence of CHDs was 9 per 1000 pregnancies. The measurement of fetal NT thickness was available in 35 of the 39 fetuses with heart defects: it was greater than or equal to3 nim in 18 (51.4%) and <3 mm in 17 (48.6%). A sensitivity of 51.4% was found at a cutoff of 3 mm. Conclusions: An increased NT thickness in chromosomally normal fetuses was found to be highly associated with CHDs and identified in more than half of the affected cases. Furthermore. an increased NT of greater than or equal to3 mm can be regarded a selection criterion for early second-trimester targeted fetal echocardiography and for increased fetal and neonatal surveillance. (C) 2002 Elsevier Science Ireland Ltd. All rights reserved

Perinatal outcome of induced and spontaneous pregnancies of primiparous women aged 35 or over

To compare the neonatal and maternal morbidity data associated with induced or naturally conceived pregnancies of primiparous women aged 35 years and older. Methods: We recruited primiparous women aged 35 years and older, who delivered between January 1995 and December 2000. The outcomes of the induced (n = 62) and naturally conceived (n = 132) pregnancies were compared. The Fisher exact test was used for univariate analysis in order to compare the delivery and pregnancy characteristics in the two groups. Results: Cesarean section featured with a 0.76 times lower prevalence among the induced pregnant women, than among the spontaneous ones, but the difference was not significant statistically. The induced pregnancies were not associated with a significantly higher rate of perinatal complications. Conclusions: Induced pregnancy does not involve a higher risk of maternal complications. The incidence of premature newborns and intrauterine growth retardation was high in both subgroups, but without a statistically significant difference. (C) 2002 International Federation of Gynecology and Obstetrics. All rights reserved