Study of C-4 deoxygenation in the biosynthesis of desosamine: evidence implicating a novel mechanism.
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Amino Sugars↗
Biomedical subjects
S Borisova
Publications and source records attributed to S Borisova.
Antibody recognition of a conformational epitope in a peptide antigen: Fv-peptide complex of an antibody fragment specific for the mutant EGF receptor, EGFRvIII.
Epitope mapping studies and the determination of the structure to 1.8 A resolution have been carried out for the antigen-binding fragment MR1 in complex with peptide antigen. MR1 is specific for the novel fusion junction of the mutant epidermal growth factor receptor EGFRvIII and has been reported to have a high degree of specificity for the mutant EGFRvIII over the wild-type EGF receptor. The structure of the complex shows that the peptide antigen residue side-chains found by epitope mapping studies to be critical for recognition are accommodated in pockets on the surface of the Fv. However, the most distinctive portion of the peptide antigen, the novel fusion glycine residue, makes no contact to the Fv and does not contribute directly to the epitope. The specificity of MR1 lies in the ability of this glycine residue to assume the restricted conformation needed to form a type II' beta-hairpin turn more easily, and demonstrates that a peptide antigen can be used to generate a conformational epitope.
ADP Ribose Transferases↗
The Structure of calnexin, an ER chaperone involved in quality control of protein folding.
The three-dimensional structure of the lumenal domain of the lectin-like chaperone calnexin determined to 2.9 A resolution reveals an extended 140 A arm inserted into a beta sandwich structure characteristic of legume lectins. The arm is composed of tandem repeats of two proline-rich sequence motifs which interact with one another in a head-to-tail fashion. Identification of the ligand binding site establishes calnexin as a monovalent lectin, providing insight into the mechanism by which the calnexin family of chaperones interacts with monoglucosylated glycoproteins.
Amino Acid Motifs↗
Identification and crystallization of a protease-resistant core of calnexin that retains biological activity.
Calnexin is a molecular chaperone that facilitates folding of glycoproteins in the endoplasmic reticulum (ER). The cloned lumenal domain of canine calnexin, cnxDeltaTMC, retains its biological activity without the transmembrane and cytosolic region. For the purpose of structure determination we generated a crystallizable core by mild proteolysis and identified its termini by N-terminal sequencing and molecular mass determination. A truncated gene was cloned accordingly. Its product, cnxDeltaN25C15, was purified to apparent homogeneity and crystallized. This truncated variant remains biologically active as shown by its binding to monoglucosylated oligosaccharides and functional interaction with ERp57. A heavy atom derivative was identified.
Amino Acid Sequence↗
Bacillus thuringiensis CryIA(a) insecticidal toxin: crystal structure and channel formation.
The activated 65 kDa lepidopteran-specific CryIA(a) toxin from the commercially most important strain Bacillus thuringiensis var. kurstaki HD-1 has been investigated by X-ray diffraction and for its ability to form channels in planar lipid bilayers. Its three-dimensional structure has been determined by a multiple isomorphous replacement method and refined at 2.25 A resolution to an R-factor of 0.168 for data with I > 2 delta (I). The toxin is made of three distinct domains. The N-terminal domain is a bundle of eight alpha-helices with the central, relatively hydrophobic helix surrounded by amphipathic helices. The middle and C-terminal domains contain mostly beta-sheets. Comparison with the structure of CryIIIA, a coleopteran-specific toxin, shows that although the fold of these two proteins is similar, there are significant structural differences within domain II. This finding supports the conclusions from genetic studies that domain II is involved in recognition and binding to cell surface receptors. The distribution of electrostatic potential on the surface of the molecule is non-uniform and identifies one side of the alpha-helical domain as negatively charged. The predominance of arginine residues as basic residues ensures that the observed positive charge distribution is also maintained in the highly alkaline environment found in the lepidopteran midgut. Structurally important salt bridges that are conserved across Cry sequences were identified and their possible role in toxin action was postulated. In planar lipid bilayers, CryIA(a) forms cation-selective channels, whose conductance is significantly smaller than that reported for CryIIIA but similar to those of other Cry toxins.
Bacillus thuringiensis↗
Crystallization and preliminary X-ray diffraction studies of the lepidopteran-specific insecticidal crystal protein CrylA(a).
A trypsin-activated CrylA(a) protein from Bacillus thuringiensis has been purified and crystallized. Crystals belong to orthorhombic space group P2(1)2(1)2(1), with cell dimensions a = 53.3, b = 111.3 and c = 154.7 A. The crystals diffract to at least 2.2 angstrum resolution and are suitable for X-ray structural analysis. They contain a single molecule in the asymmetric unit.
Animals↗
Self-irradiation effect on yeast cells.
The effect of self irradiation on yeast cells has been investigated by counting the young gemmae formation in 104 self irradiated samples, as compared with an equal set of control samples. The results show that the rate of gemmae formation is higher in self irradiated samples; the statistical significance of the results is discussed.
Radiation↗