Biomedical subjects

Janusz Stepinski

Publications and source records attributed to Janusz Stepinski.

26 records · Page 2Linked to original sources

PubMed2002

Biophysical studies of eIF4E cap-binding protein: recognition of mRNA 5' cap structure and synthetic fragments of eIF4G and 4E-BP1 proteins.

mRNA 5'-cap recognition by the eukaryotic translation initiation factor eIF4E has been exhaustively characterized with the aid of a novel fluorometric, time-synchronized titration method, and X-ray crystallography. The association constant values of recombinant eIF4E for 20 different cap analogues cover six orders of magnitude; with the highest affinity observed for m(7)GTP (approximately 1.1 x 10(8) M(-1)). The affinity of the cap analogues for eIF4E correlates with their ability to inhibit in vitro translation. The association constants yield contributions of non-covalent interactions involving single structural elements of the cap to the free energy of binding, giving a reliable starting point to rational drug design. The free energy of 7-methylguanine stacking and hydrogen bonding (-4.9 kcal/mol) is separate from the energies of phosphate chain interactions (-3.0, -1.9, -0.9 kcal/mol for alpha, beta, gamma phosphates, respectively), supporting two-step mechanism of the binding. The negatively charged phosphate groups of the cap act as a molecular anchor, enabling further formation of the intermolecular contacts within the cap-binding slot. Stabilization of the stacked Trp102/m(7)G/Trp56 configuration is a precondition to form three hydrogen bonds with Glu103 and Trp102. Electrostatically steered eIF4E-cap association is accompanied by additional hydration of the complex by approximately 65 water molecules, and by ionic equilibria shift. Temperature dependence reveals the enthalpy-driven and entropy-opposed character of the m(7)GTP-eIF4E binding, which results from dominant charge-related interactions (DeltaH degrees =-17.8 kcal/mol, DeltaS degrees= -23.6 cal/mol K). For recruitment of synthetic eIF4GI, eIF4GII, and 4E-BP1 peptides to eIF4E, all the association constants were approximately 10(7) M(-1), in decreasing order: eIF4GI>4E-BP1>eIF4GII approximately 4E-BP1(P-Ser65) approximately 4E-BP1(P-Ser65/Thr70). Phosphorylation of 4E-BP1 at Ser65 and Thr70 is insufficient to prevent binding to eIF4E. Enhancement of the eIF4E affinity for cap occurs after binding to eIF4G peptides.

Adaptor Proteins, Signal Transducing↗

PubMed2002

The g5R (D250) gene of African swine fever virus encodes a Nudix hydrolase that preferentially degrades diphosphoinositol polyphosphates.

The African swine fever virus (ASFV) g5R gene encodes a protein containing a Nudix hydrolase motif which in terms of sequence appears most closely related to the mammalian diadenosine tetraphosphate (Ap4A) hydrolases. However, purified recombinant g5R protein (g5Rp) showed a much wider range of nucleotide substrate specificity compared to eukaryotic Ap4A hydrolases, having highest activity with GTP, followed by adenosine 5'-pentaphosphate (p5A) and dGTP. Diadenosine and diguanosine nucleotides were substrates, but the enzyme showed no activity with cap analogues such as 7mGp3A. In common with eukaryotic diadenosine hexaphosphate (Ap6A) hydrolases, which prefer higher-order polyphosphates as substrates, g5Rp also hydrolyzes the diphosphoinositol polyphosphates PP-InsP5 and [PP]2-InsP4. A comparison of the kinetics of substrate utilization showed that the k(cat)/K(m) ratio for PP-InsP5 is 60-fold higher than that for GTP, which allows classification of g5R as a novel diphosphoinositol polyphosphate phosphohydrolase (DIPP). Unlike mammalian DIPP, g5Rp appeared to preferentially remove the 5-beta-phosphate from both PP-InsP5 and [PP]2-InsP4. ASFV infection led to a reduction in the levels of PP-InsP5, ATP and GTP by ca. 50% at late times postinfection. The measured intracellular concentrations of these compounds were comparable to the respective K(m) values of g5Rp, suggesting that one or all of these may be substrates for g5Rp during ASFV infection. Transfection of ASFV-infected Vero cells with a plasmid encoding epitope-tagged g5Rp suggested localization of this protein in the rough endoplasmic reticulum. These results suggest a possible role for g5Rp in regulating a stage of viral morphogenesis involving diphosphoinositol polyphosphate-mediated membrane trafficking.

Acid Anhydride Hydrolases↗

PubMedDate not supplied

Synthesis of novel mRNA 5' cap-analogues: dinucleoside P1, P3-tri-, P1, P4-tetra-, and P1, P5-pentaphosphates.

A series of new mRNA anti reverse cap analogues (ARCA) was designed to obtain a tool for studying the mechanism of protein translation. Dinucleoside P1, P3-tri-, P1, P4-tetra- and P1, P5-pentaphosphates, linked by a 5'-to-5' phosphate bridge and composed of modified 7-methylguanosine and guanosine, have been synthesized. The hydroxyl group (2'OH or 3'OH) in 7-metylguanosine moiety was replaced by -OCH3 or -H in order to obtain the cap analogues capable to be correctly incorporated into synthetic mRNA transcripts. Tri-, tetra-, and pentaphosphates were prepared by ZnCl2 catalyzed condensation in DMF of derivatives of the 7-methylguanosine diphosphates with the guanosine mono-, di- and triphosphate P-imidazolides, respectively. The structures of the novel compounds were established by means of 1H and 31P NMR spectra.

Dinucleoside Phosphates↗

PubMedDate not supplied

Partial molar volumes of mRNA 5' cap analogues.

Partial molar volumes in aqueous solution of eleven selected 7-methylguanine cap-analogues and their guanine counterparts were determined by means of density measurements. Hydrophobicity of the investigated compounds regarding their structural features was analysed within the framework of the solute-solvent interaction model, based on the relative density of the molecular solvation shell.

Guanine↗

PubMedDate not supplied

Thermodynamics of 7-methylguanosine cation stacking with tryptophan upon mRNA 5' cap binding to translation factor eIF4E.

All eukaryotic nuclear transcribed mRNAs possess the cap structure, consisting of 7-methylguanosine linked by the 5'-5' triphosphate bridge to the first nucleoside. The goal of the present study is to dissect the enthalpy and entropy changes of association of the mRNA 5' cap with eIF4E into contributions originating from the interaction of 7-methylguanosine with tryptophan. The model results are discussed in the context of the thermodynamic parameters for the association of eIF4E with synthetic cap analogues.

Binding Sites↗

PubMedDate not supplied

Binding studies of eukaryotic initiation factor eIF4E with novel mRNA dinucleotide cap analogues.

Studies on the interaction of the murine translation initiation factor 4E with two new-synthesized cap-analogues, modified at C2' of 7-methylguanosine, have been performed by means of the fluorescence titration method. No difference in the binding affinity for eIF4E was observed compared with the "anti reversed" cap analogues, possessing the analogous modifications at C3'. Potential significance of the novel caps as research tools for examination of the nuclear cap binding complex CBC80/20 has been discussed.

Animals↗

PubMedDate not supplied

Influence of the length of the phosphate chain in mRNA 5' cap analogues on their interaction with eukaryotic initiation factor 4E.

The recognition of the 5'mRNA cap structure m7G(5')ppp(5')N by one of the components of the initiation translation machinery, the eIF4E factor, plays a pivotal role in regulation of the protein synthesis. In the present study we have shown two opposing roles of the cap phosphate chain in the specific eIF4E-cap interaction. The extension of the phosphate chain enhances the binding of the cap to the unphosphorylated eIF4E but destabilises the eIF4E-cap complex in case of the phosphorylated protein.

Eukaryotic Initiation Factor-4E↗

PubMedDate not supplied

Interaction between yeast eukaryotic initiation factor eIF4E and mRNA 5' cap analogues differs from that for murine eIF4E.

Measurements of interaction of 7-methyl-GTP eIF4E from S. cerevisiae were performed by means of two methods: Isothermal Titration Calorimetry (ITC) and fluorescence titration. The equilibrium association constants (Kas) derived from the two methods show significantly different affinity of yeast eIF4E for the mRNA 5' cap than those of the murine and human proteins. The observed differences in the Kas values and the enthalpy changes of the association (deltaH(o)) suggest some dissimilarity in the mode of binding and stabilization of cap in the complexes with eIF4E from various sources.

Animals↗