Hydrogen bonds in galactopyranoside and glucopyranoside: a density functional theory study

Density functional theory calculations on two glycosides, namely, n-octyl-β-D-glucopyranoside (C₈O-β-Glc) and n-octyl-β-D-galactopyranoside (C₈O-β-Gal) were performed for geometry optimization at the B3LYP/6-31G level. Both molecules are stereoisomers (epimers) differing only in the orientation of the hydroxyl group at the C4 position. Thus it is interesting to investigate electronically the effect of the direction (axial/equatorial) of the hydroxyl group at the C4 position. The structure parameters of X-H???Y intramolecular hydrogen bonds were analyzed, while the nature of these bonds and the intramolecular interactions were considered using the atoms in molecules (AIM) approach. Natural bond orbital analysis (NBO) was used to determine bond orders, charge and lone pair electrons on each atom and effective non-bonding interactions. We have also reported electronic energy and dipole moment in gas and solution phases. Further, the electronic properties such as the highest occupied molecular orbital, lowest unoccupied molecular orbital, ionization energy, electron affinity, electronic chemical potential, chemical hardness, softness and electrophilicity index, are also presented here for both C₈O-β-Glc and C₈O-β-Gal. These results show that, while C₈O-β-Glc possess– only one hydrogen bond, C₈O-β-Gal has two intramolecular hydrogen bonds, which further confirms the anomalous stability of the latter in self-assembly phenomena.     

Functional Characterization of Probiotic Potential of Novel Pigmented Bacterial Strains for Aquaculture Applications

Probiotics and Antimicrobial Proteins - The bioprospecting proficient of novel pigmented probiotic strains with respect to aquaculture industry was unexplored hitherto. In this study, we...     

Quinone methides—and not dehydrodopamine derivatives—as reactive intermediates of β-sclerotization in the puparia of flesh fly Sarcophaga bullata

Cuticular phenoloxidase(s) from Sarcophaga bullata larvae oxidized a variety of o-diphenolic compounds. While catechol, 3,4-dihydroxybenzoic acid, dopa, dopamine, and norepinephrine were converted to their corresponding quinone derivatives, other catechols such as 3,4-dihydroxyphenylacetic acid, 3,4-dihydroxyphenethyl alcohol, 3,4-dihydroxyphenyl glycol, 3,4-dihy-droxymandelic acid, and N-acetyldopamine were oxidized to their side-chain oxygenated products. In addition, the enzyme-catalyzed oxidation of the latter group of compounds accompanied the formation of colorless catecholcuticle adducts consistent with the operation of β-sclerotization. Radioactive trapping experiments failed to support the participation of 1,2-dehydro-N-acetyldopamine as a freely formed intermediate during phenoloxidase-mediated oxidation of N-acetyldopamine. When specifically tritiated substrates were provided, cuticular enzyme selectively removed tritium from [7-³H]N-acetyldopamine and not from either [8-³H] or [ring-³H]N-acetyldopamine during the initial phase of oxidation. The above results are consistent with the generation and subsequent reactions of quinone methides as the initial products of enzyme-catalyzed N-acetyldopamine oxidation and confirm our hypothesis that quinone methides and not 1,2-dehydro-N-acetyldopamine are the reactive intermediate of β-sclerotization of sarcophagid cuticle. Quinone methide sclerotization resolves a number of conflicting observations made by previous workers in this field.     

Proteolytic Cleavage of Type I Collagen Generates an Autoantigen in Autoimmune Uveitis

This study was initiated to induce experimental autoimmune anterior uveitis (EAAU) in Lewis rats by melanin-associated antigen (MAA; 22-kDa fragment of type I collagen α2 chain) derived from rat iris and ciliary body (CB), to localize MAA within the eye, and to investigate the possible mechanism of MAA generation in vivo. The EAAU model replicates idiopathic human anterior uveitis. Lewis rats sensitized to rat MAA developed anterior uveitis, and EAAU induced by rat MAA can be adoptively transferred to naive syngenic rats by MAA-primed T cells. Animals immunized with rat MAA developed cellular immunity to the antigen. MAA was detected only in the iris and CB of the eye. Iris and CB were the major source of matrix metalloproteinase-1 (MMP-1) in the naive eye, and ocular expression of MMP-1 was up-regulated, whereas expression of tissue inhibitor of metalloproteinase 1 decreased before the onset of EAAU. These results demonstrated that EAAU can be induced by autologous MAA. Uveitogenic antigen is present only in the iris and CB of the eye, and the imbalance between MMP-1 and tissue inhibitor of metalloproteinase 1 may play a role in the generation of MAA in vivo. Collectively, the evidence presented here suggests that MAA is an autoantigen in EAAU. These observations may extend to idiopathic human anterior uveitis and facilitate the development of antigen-specific therapy.     

Homepeptide Repeats:Implications for Protein Structure,Function and Evolution

Analysis of protein sequences from Mycobacterium tuberculosis H37Rv(Mtb H37Rv) was performed to identify homopeptide repeatcontaining proteins(HRCPs).Functional annotation of the HRCPs showed that they are preferentially involved in cellular metabolism.Furthermore,these homopeptide repeats might play some specific roles in protein-protein interaction.Repeat length differences among Bacteria,Archaea and Eukaryotes were calculated in order to identify the conservation of the repeats in these divergent kingdoms.From the results,it was evident that these repeats have a higher degree of conservation in Bacteria and Archaea than in Eukaryotes.In addition,there seems to be a direct correlation between the repeat length difference and the degree of divergence between the species.Our study supports the hypothesis that the presence of homopeptide repeats influences the rate of evolution of the protein sequences in which they are embedded.Thus,homopeptide repeat may have structural,functional and evolutionary implications on proteins.     

Functional mapping of community‐acquired respiratory distress syndrome (CARDS) toxin of Mycoplasma pneumoniae defines regions with ADP‐ribosyltransferase,vacuolating and receptor‐binding activities

Community‐acquired respiratory distress syndrome (CARDS) toxin from Mycoplasma pneumoniae is a 591‐amino‐acid virulence factor with ADP‐ribosyltransferase (ADPRT) and vacuolating activities. It is expressed at low levels during in vitro growth and at high levels during colonization of the lung. Exposure of experimental animals to purified recombinant CARDS toxin alone is sufficient to recapitulate the cytopathology and inflammatory responses associated with M. pneumoniae infection in humans and animals. Here, by molecular modelling, serial truncations and site‐directed mutagenesis, we show that the N‐terminal region is essential for ADP‐ribosylating activity. Also, by systematic truncation and limited proteolysis experiments we identified a portion of the C‐terminal region that mediates toxin binding to mammalian cell surfaces and subsequent internalization. In addition, the C‐terminal region alone induces vacuolization in a manner similar to full‐length toxin. Together, these data suggest that CARDS toxin has a unique architecture with functionally separable N‐terminal and C‐terminal domains.     

Isolation and function of a low molecular weight protein of mung bean embryonic axes

A low molecular weight protein from dry mung bean (Vigna radiata) embryonic axes has been purified to near homogeneity by chromatography on DEAE-cellulose and hydroxylapatite. It shows a molecular weight of about 12,000 in sodium dodecyl sulfate-polyacrylamide gels and a sedimentation coefficient of about 2 S in sucrose gradients. This protein occurs in greater amounts in dry axes than in dry cotyledons, and it dramatically disappears during early germination of the seed. Affinity chromatography tests do not indicate it as a trypsin inhibitor or as a glycoprotein. It is a water-soluble cytoplasmic protein exhibiting an amino acid composition characteristic of storage proteins with a high content of glutamic acid/glutamine. We suggest that it is a low molecular weight storage albumin.Abbreviations Asx aspartic acid/asparagine - BSA bovine serum albumin - Con A concanavalin A - EB extraction buffer - Glx glutamic acid/glutamine - HA hydroxylapatite - PB phosphate buffer - SDS-PAGE sodium dodecyl sulfate-polyacrylamide gel electrophoresis - TCA trichloroacetic acid