Uma V Katre

CSIR - National Chemical Laboratory, Pune, Poona, Maharashtra, India

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Publications (6)13.92 Total impact

  • Urvashi Sharma · Uma V. Katre · C. G. Suresh
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    ABSTRACT: Main conclusion Crystal structure of a reported PA2 albumin from Cicer arietinum shows that it belongs to hemopexin fold family, has four beta-propeller motifs and possesses hemagglutination activity, making it different from known legume lectins. A plant albumin (PA2) from Cicer arietinum, presumably a lectin (CAL) owing to its hemagglutination activity which is inhibited by complex sugars as well as glycoproteins such as fetuin, desialylated fetuin and fibrinogen. The three-dimensional structure of this homodimeric protein has been determined using X-ray crystallography at 2.2 Å in two crystal forms: orthorhombic (P21212) and trigonal (P3). The structure determined using molecular replacement method and refined in orthorhombic crystal form reached R-factors R free 22.6 % and R work 18.2 % and in trigonal form had 22.3 and 17.9 % in the resolution range of 20.0–2.2 and 35.3–2.2 Å, respectively. Interestingly, unlike the known legume lectin fold, the structure of this homodimeric hemagglutinin belonged to hemopexin fold that consisted of four-bladed β-propeller architecture. Each subunit has a central cavity forming a channel, inside of which is lined with hydrophobic residues. The channel also bears binding sites for ligands such as calcium, sodium and chloride ions, iodine atom in the case of iodine derivative and water molecules. However, none of these ligands seem important for the sugar recognition. No monosaccharide sugar specificity could be detected using hemagglutination inhibition. Chemical modification studies identified a potential sugar-binding site per subunit molecule. Comparison of C-alpha atom positions in subunit structures showed that the deviations between the two crystal forms were more with respect to blades I and IV. Differences also existed between subunits in two forms in terms of type and site of ligand binding.
    No preview · Article · Jan 2015 · Planta
  • Uma V Katre · C G Suresh
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    ABSTRACT: The crystal structures of proteins showing homotetrameric association, a common feature observed in many lectins, have been analyzed in order to understand the characteristics of tetrameric association in terms of the arrangement of subunits and their biological significance. The analysis could group the tetramer units into the following four categories. (i) Tetrahedral molecules, in which the four monomers form a nearly perfect tetrahedral arrangement. The angle between the axes of any two monomers is approximately 109 degrees. (ii) Molecules that form a sandwiched dimer of dimers in which the two dimers are arranged perpendicular to each other, one upon the other. (iii) Planar molecules, in which the four monomers lie in one plane and the corresponding sides of adjacent monomers face in opposite directions. This can be considered as a flattened tetrahedral shape. (iv) Planar closed molecules, in which all four monomers lie in one plane arranged in a head-to-tail fashion in a square. The first group and its variant, the third group, are the most commonly found arrangements in crystal structures. Each arrangement has its own importance for biological function. Some tetrameric assemblies that deviate from the majority described above also have relevance to their biological function.
    No preview · Article · Feb 2009 · Acta Crystallographica Section D Biological Crystallography
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    ABSTRACT: The hemagglutinin from the seeds of Moringa oleifera (MoL) agglutinates human as well as rabbit erythrocytes; the affinity for the latter is almost 250 times more than that for the former. MoL was inhibited by glycoproteins namely thyroglobulin, fetuin and holotransferin indicating the complex sugar specificity of the lectin. The protein is a homodimer with molecular mass of 14kDa, subunits (7.1kDa) linked by the disulfide bond(s). The secondary structure elements of MoL are alpha-helix, 28%; beta-sheet, 23%; turn 20% and unordered 28%. While the activity and secondary structure were not affected at extreme pH and high temperature, they were drastically affected in presence of dithiothreitol at and above pH 7.0, indicating that disulfide linkages hold the active conformation of the protein.
    No preview · Article · Apr 2008 · International Journal of Biological Macromolecules
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    ABSTRACT: The saccharide binding and conformational characterization of a hemagglutinin, a low molecular weight protein from the seeds of Moringa oleifera was studied using steady state and time resolved fluorescence. The lectin binds sugars LacNAc (K a = 1380 M−1) and fructose (K a = 975 M−1), as determined by the fluorescence spectroscopy. It has a single tryptophan per monomer which is exposed on the surface and is in a strong electropositive environment as revealed by quenching with iodide. Quenching of the fluorescence by acrylamide involved both static (K s = 0.216 M−1) and collisional (K sv = 8.19 M−1) components. The native protein showed two different lifetimes, τ 1 (1.6 ns) and τ 2 (4.36 ns) which decrease and get converted into a single one, (2.21 ns) after quenching with 0.15 M acrylamide. The bimolecular quenching constant, k q was 7.55 × 1011 M−1 s−1. ANS binding studies showed that the native protein has exposed hydrophobic patches which get further exposed at extreme acidic or alkaline pH. However, they get buried in the interior of the protein in presence of 1 M GdnHCl or urea.
    No preview · Article · Apr 2008 · Journal of Fluorescence
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    ABSTRACT: The lectin isolated from mature seeds of Cicer arietinum (CAL) agglutinates pronase-treated rabbit and human erythrocytes and its haemagglutination activity is inhibited by fetuin and desialated fetuin but not by simple monosaccharides or oligosaccharides. The purified lectin is a dimer of molecular weight 43,000 Da composed of two identical subunits (MW 21,500), as confirmed by SDS-PAGE. The lectin has been crystallized using the hanging-drop vapour-diffusion method at 295 K over a well solution containing 0.2 M sodium acetate, 0.1 M sodium phosphate buffer pH 6.5 and 14%(w/v) polyethylene glycol 8000. The triangular prism-shaped crystals belong to space group R3 and have unit-cell parameters a = b = 81.2, c = 69.4 A. The diffraction data are 93.8% complete to 2.3 A Bragg spacing with an Rmerge of 0.103.
    Full-text · Article · Feb 2005 · Acta Crystallographica Section F Structural Biology and Crystallization Communications
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    K N Rao · C G Suresh · U V Katre · S M Gaikwad · M I Khan
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    ABSTRACT: Based on their carbohydrate specificity, the jacalin family of lectins can be divided into two groups: galactose-specific and mannose-specific. The former are cytoplasmic proteins, whereas the latter are localized in the storage vacuoles of cells. It has been proposed that the post-translational modification in some of the lectins that splits their polypeptide chains into two may be crucial for galactose specificity. The mannose-specific members of the family are single-chain proteins that lack the above modification. Although the galactose-specific and the mannose-specific jacalin-type lectins differ in their sequences, they share a common fold: the beta-prism I fold, which is characteristic of Moraceae plant lectins. Here, two crystal structures of a jacalin-related lectin from Artocarpus hirsuta, which is specific for galactose, in complex with methyl-alpha-D-galactose are reported. The lectin crystallized in two orthorhombic forms and one hexagonal form under similar conditions. The crystals had an unusually high solvent content. The structure was solved using the molecular-replacement method using the jacalin structure as a search model. The two orthorhombic forms were refined using data to 2.5 and 3.0 A resolution, respectively. The structures of the A. hirsuta lectin and jacalin are identical. In orthorhombic form I the crystal packing provides three different micro-environments for sugar binding in the same crystal. The observed difference in the specificity for oligosaccharides between the A. hirsuta lectin and jacalin could only be explained based on differences in the molecular associations in the packing and variation of the C-terminal length of the beta-chain. The observed insecticidal activity of A. hirsuta lectin may arise from its similar fold to domain II of the unrelated delta-endotoxin from Bacillus thuringiensis.
    Full-text · Article · Sep 2004 · Acta Crystallographica Section D Biological Crystallography