Network


Latest external collaboration on country level. Dive into details by clicking on the dots.

Hotspot


Dive into the research topics where Petya Christova is active.

Publication


Featured researches published by Petya Christova.


Journal of Biological Chemistry | 2003

Xeroderma Pigmentosum Group C Protein Possesses a High Affinity Binding Site to Human Centrin 2 and Calmodulin

Aurel Popescu; Simona Miron; Y. Blouquit; Patricia Duchambon; Petya Christova; Constantin T. Craescu

Human centrin 2 (HsCen2), a member of the EF-hand superfamily of Ca2+-binding proteins, is commonly associated with centrosome-related structures. The protein is organized in two domains, each containing two EF-hand motifs, but only the C-terminal half exhibits Ca2+ sensor properties. A significant fraction of HsCen2 is localized in the nucleus, where it was recently found associated with the xeroderma pigmentosum group C protein (XPC), a component of the nuclear excision repair pathway. Analysis of the XPC sequence (940 residues), using a calmodulin target recognition software, enabled us to predict two putative binding sites. The binding properties of the two corresponding peptides were investigated by isothermal titration calorimetry. Only one of the peptides (P1-XPC) interacts strongly (Ka = 2.2 × 108 m-1, stoichiometry 1:1) with HsCen2 in a Ca2+-dependent manner. This peptide also binds, with a similar affinity (Ka = 1.1 × 108 m-1) to a C-terminal construct of HsCen2, indicating that the interaction with the integral protein is mainly the result of the contribution of the C-terminal half. The second peptide (P2-XPC) failed to show any detectable binding either to HsCen2 or to its C-terminal lobe. The two peptides interact with different affinities and mechanisms with calmodulin. Circular dichroism and nuclear magnetic resonance were used to structurally characterize the complex formed by the C-terminal domain of HsCen2 with P1-XPC.


Biochimica et Biophysica Acta | 1988

pH-dependence of photo-induced electron transfer in zinc-substituted sperm whale myoglobin

Alexandra Shosheva; Petya Christova; Boris P. Atanasov

The electron transfer between the excited triplet state of zinc-substituted sperm whale myoglobin and Cu2+ has been studied by following the decay rate of delayed fluorescence. The Cu2+ bound on the surface of the myoglobin molecule are efficient quenchers of the excited electron state of Zn-myoglobin. Two bimolecular rate constants of quenching (KQ) for every pH investigated have been calculated. The pH-dependence of KQ1 indicates that the protonation of one amino acid residue (His-GH1 (119] is important for the process. Our results support the idea of the common nature of the mechanism of quenching by Cu2+ and oxidation of oxymyoglobin by Cu2+.


Journal of Bioinformatics and Computational Biology | 2007

ASSESSING THE QUALITY OF THE HOMOLOGY-MODELED 3D STRUCTURES FROM ELECTROSTATIC STANDPOINT: TEST ON BACTERIAL NUCLEOSIDE MONOPHOSPHATE KINASE FAMILIES

Petras J. Kundrotas; Paulina Georgieva; Alexandra Shosheva; Petya Christova; Emil Alexov

In this study, we address the issue of performing meaningful pK(a) calculations using homology modeled three-dimensional (3D) structures and analyze the possibility of using the calculated pK(a) values to detect structural defects in the models. For this purpose, the 3D structure of each member of five large protein families of a bacterial nucleoside monophosphate kinases (NMPK) have been modeled by means of homology-based approach. Further, we performed pK(a) calculations for the each model and for the template X-ray structures. Each bacterial NMPK family used in the study comprised on average 100 members providing a pool of sequences and 3D models large enough for reliable statistical analysis. It was shown that pK(a) values of titratable groups, which are highly conserved within a family, tend to be conserved among the models too. We demonstrated that homology modeled structures with sequence identity larger than 35% and gap percentile smaller than 10% can be used for meaningful pK(a) calculations. In addition, it was found that some highly conserved titratable groups either exhibit large pK(a) fluctuations among the models or have pK(a) values shifted by several pH units with respect to the pK(a) calculated for the X-ray structure. We demonstrated that such case usually indicates structural errors associated with the model. Thus, we argue that pK(a) calculations can be used for assessing the quality of the 3D models by monitoring fluctuations of the pK(a) values for highly conserved titratable residues within large sets of homologous proteins.


Zeitschrift für Naturforschung C | 2003

Fluorescence Studies on Denaturation and Stability of Recombinant Human Interferon-Gamma

Petya Christova; Kristina Todorova; Ilijana Timtcheva; Genoveva Nacheva; Andrey Karshikoff; Peter Nikolov

Unfolding/folding transitions of recombinant human interferon-gamma (hIFNγ) in urea and guanidine chloride (Gn.HCl) solutions were studied by fluorescence spectroscopy. At pH 7.4 Gn.HCl was a much more efficient denaturant (midpoint of unfolding C* = 1.1 m and ΔG0 = 13.4 kJ/mol) than urea (C* = 2.8 m and ΔG0 = 11.7 kJ/mol). The close ΔG0 values indicate that the contribution of electrostatic interactions to the stability of hIFNγ is insignificant. Both the pH dependence of the fluorescence intensity and the unfolding experiments in urea at variable pH showed that hIFNγ remains native in the pH range of 4.8-9.5. Using two quenchers, iodide and acrylamide, and applying the Stern-Volmer equation, a cluster of acidic groups situated in close proximity to the single tryptophan residue was identified. Based on the denaturation experiments at different pH values and on our earlier calculations of the electrostatic interactions in hIFNγ, we assume that the protonation of Asp63 causes conformational changes having a substantial impact on the stability of hIFNγ.


Acta Crystallographica Section F-structural Biology and Crystallization Communications | 2006

Crystallization and preliminary X-ray diffraction data of the complex between human centrin 2 and a peptide from the protein XPC

Jean-Baptiste Charbonnier; Petya Christova; Alexandra Shosheva; Enrico A. Stura; Marie Hélène Le Du; Y. Blouquit; Patricia Duchambon; Simona Miron; Constantin T. Craescu

Centrins are highly conserved calcium-binding proteins involved in the nucleotide-excision repair pathway as a subunit of the heterotrimer including the XPC and hHR23B proteins. A complex formed by a Ca2+-bound human centrin 2 construct (the wild type lacking the first 25 amino acids) with a 17-mer peptide derived from the XPC sequence (residues Asn847-Arg863) was crystallized. Data were collected to 1.65 angstroms resolution from crystals grown in 30% monomethyl polyethylene glycol (MPEG) 500, 100 mM NaCl and 100 mM Bicine pH 9.0. Crystals are monoclinic and belong to space group C2, with two molecules in the asymmetric unit. The unit-cell parameters are a = 60.28, b = 59.42, c = 105.14 angstroms, alpha = gamma = 90, beta = 94.67 degrees. A heavy-atom derivative was obtained by co-crystallization with Sr2+. The substitution was rationalized by calorimetry experiments, which indicate a binding constant for Sr2+ of 4.0 x 10(4) M(-1).


Zeitschrift für Naturforschung C | 2009

Some physicochemical peculiarities of poplar plastocyanins a and b.

Petya Christova; Anthony A. Donchev; Alexandra Shosheva; Vladimir I. Getov; Mitko Dimitrov

The redox potentials of poplar plastocyanins a and b (PCa, PCb) were determined by spectro photometric titrations of their reduced forms with [Fe(CN)6]3-. It was found that the two isoforms have the following millimolar extinction coefficients ε597, equilibrium constants Keq of one-electron exchange with [Fe(CN)6]4-/[Fe(CN)6]3-, and standard electron potentials E0′: PCa: ε597 = (4.72 ± 0.08) mM-1 cm-1, Keq = 0.133 ± 0.009, E0′ = (354 ± 11) mV; PCb: ε597 = (5.23 ± 0.16) mM-1 cm-1, Keq = 0.175 ± 0.010, E0′ = (363 ± 12) mV. The pH dependence of the redox potential of PCb was studied too. It was found, that the value of E0′ for PCb is constant in the pH range 6.5 - 9.5, but decreases in the range 4.8 - 6.5. On the whole, the dependence resembles that of PC from some well-known plant species, including poplar PCa. The changes of E0′ in the pH-dependent region for poplar PCb, however, are smaller and are 13 mV per pH unit, whereas in the other well-known plant species the changes are about 50 - 60 mV per pH unit. It has been assumed that the weaker pH dependence of E0′ of PCb accounts for some structural differences between PCa and PCb


Zeitschrift für Naturforschung C | 2010

Physicochemical Characteristics of a Thermostable Gellan Lyase from Geobacillus stearothermophilus 98

Anna Derekova; Miroslava Atanassova; Petya Christova; Bojidar Tchorbanov; Alexandra Shosheva; Rossitsa Mandeva; Patricia Rodríguez-Alonso; J.I. Garabal; Margarita Kambourova

A purified thermostable gellan lyase, produced by a thermophilic bacterium, Geobacillus stearothermophilus 98, was characterized in relation to its physicochemical properties. The gellan lyase was established to have a molecular weight of 216 kDa, defined by capillary gel electrophoresis. Amino acid analysis revealed high quantities of Lys, His, Ala, Val, Ile, Glx, and Pro residues. The circular dichroism revealed 45% β-structure and practically lack of α-spiral domains. Kinetic studies showed high affinity of the enzyme to gellan as a substrate (Km = 0.21 μM). The thermal denaturation investigated by cicular dichroism showed a highly cooperative transition with a midpoint (Tm) at about 75 °C. A single product was identified after enzyme action on gellan. Large exothermic aggregation near Tm was observed by differential scanning calorimetry. Two types of gellan lyase crystals were reproducibly isolated.


Journal of Photochemistry and Photobiology B-biology | 1993

Urea unfolding and stability of gamma-II crystallin

Alexandra Shosheva; Petya Christova; Velin Z. Spassov; Boris P. Atanasov

The conformational stability of gamma-II crystallin at pH 7.0 was estimated by studying its urea denaturation at isothermal conditions. The conformational states were monitored by far UV-CD and fluorescence measurements. Gamma-II crystallin shows sigmoidal order-disorder transition curves by both methods. The presence of more than one intermediate was confirmed but at neutral pH. The experiment results were critically analyzed in terms of both linear extrapolation and Tanfords models. The Gibbs free energy of unfolding delta G u,H2O = -36 kcal mol-1 was obtained. This value corresponds to the high conformational stability of the protein predicted qualitatively by its crystal structure.


Journal of Molecular Biology | 2007

Structural, thermodynamic, and cellular characterization of human centrin 2 interaction with xeroderma pigmentosum group C protein.

Jean-Baptiste Charbonnier; Emilie Renaud; Simona Miron; Marie Hélène Le Du; Y. Blouquit; Patricia Duchambon; Petya Christova; Alexandra Shosheva; Thierry Rose; Jaime F. Angulo; Constantin T. Craescu


Biochemistry | 2002

Mechanism of domain closure of Sec7 domains and role in BFA sensitivity.

Louis Renault; Petya Christova; Bernard Guibert; Jacqueline Cherfils

Collaboration


Dive into the Petya Christova's collaboration.

Top Co-Authors

Avatar

Alexandra Shosheva

Bulgarian Academy of Sciences

View shared research outputs
Top Co-Authors

Avatar

Boris P. Atanasov

Bulgarian Academy of Sciences

View shared research outputs
Top Co-Authors

Avatar
Top Co-Authors

Avatar
Top Co-Authors

Avatar
Top Co-Authors

Avatar
Top Co-Authors

Avatar

Anthony A. Donchev

Bulgarian Academy of Sciences

View shared research outputs
Top Co-Authors

Avatar

Mitko Dimitrov

Bulgarian Academy of Sciences

View shared research outputs
Top Co-Authors

Avatar

Paulina Georgieva

Bulgarian Academy of Sciences

View shared research outputs
Top Co-Authors

Avatar

Vladimir I. Getov

Bulgarian Academy of Sciences

View shared research outputs
Researchain Logo
Decentralizing Knowledge