Structure and solution properties of tamarind-seed polysaccharide

The major polysaccharide in tamarind seed is a galactoxyloglucan for which the ratios galactose:xylose:glucose are 1:2:25:2.8. A minor polysaccharide (2-3%) contains branched (1----5)-alpha-L-arabinofuranan and unbranched (1----4)-beta-D-galactopyranan features. Small-angle X-ray scattering experiments gave values for the cross-sectional radius of the polymer in aqueous solution that were typical of single-stranded molecules. Marked stiffness of the chain (C infinity 110) was deduced from static light-scattering studies and is ascribed partially to the restriction of the motion of the (1----4)-beta-D-glucan backbone by its extensive (approximately 80%) glycosylation. The rigidity of the polymer caused significant draining effects which heavily influenced the hydrodynamic behaviour. The dependence of "zero-shear" viscosity on concentration was used to characterise "dilute" and "semi-dilute" concentration regimes. The marked dependence on concentration in the "semi-dilute" region was similar to that for other stiff neutral polysaccharide systems, ascribed to "hyper-entanglements", and it is suggested that these may have arisen through a tenuous alignment of stiffened chains.

The conserved noncatalytic 40-residue sequence in cellulases and hemicellulases from anaerobic fungi functions as a protein docking domain

Two cDNAs, designated xynA and manA, encoding xylanase A (XYLA) and mannanase A (MANA), respectively, were isolated from a cDNA library derived from mRNA extracted from the anaerobic fungus, Piromyces. XYLA and MANA displayed properties typical of endo-beta 1,4-xylanases and mannanases, respectively. Neither enzyme hydrolyzed cellulosic substrates. The nucleotide sequences of xynA and manA revealed open reading frames of 1875 and 1818 base pairs, respectively, coding for proteins of M(r) 68,049 (XYLA) and 68,055 (MANA). The deduced primary structure of MANA revealed a 458-amino acid sequence that exhibited identity with Bacillus and Pseudomonas fluorescens subsp. cellulosa mannanases belonging to glycosyl hydrolase Family 26. A 40-residue reiterated sequence, which was homologous to duplicated noncatalytic domains previously observed in Neocallimastix patriciarum xylanase A and endoglucanase B, was located at the C terminus of MANA. XYLA contained two regions that exhibited sequence identity with the catalytic domains of glycosyl hydrolase Family 11 xylanases and were separated by a duplicated 40-residue sequence that exhibited strong homology to the C terminus of MANA. Analysis of truncated derivatives of MANA confirmed that the N-terminal 458-residue sequence constituted the catalytic domain, while the C-terminal domain was not essential for the retention of catalytic activity. Similar deletion analysis of XYLA showed that the C-terminal catalytic domain homologue exhibited catalytic activity, but the corresponding putative N-terminal catalytic domain did not function as a xylanase. Fusion of the reiterated noncatalytic 40-residue sequence conserved in XYLA and MANA to glutathione S-transferase, generated a hybrid protein that did not associate with cellulose, but bound to 97- and 116-kDa polypeptides that are components of the multienzyme cellulase-hemicellulase complexes of Piromyces and Neocallimastix patriciarum, respectively. The role of this domain in the assembly of the enzyme complex is discussed.

Phage display of peptide epitopes from HIV-1 elicits strong cytolytic responses

Although much effort has been expended on evaluating recombinant proteins and synthetic peptides as immunogens, they have generally proved incapable of inducing an efficient cytotoxic T-cell (CTL) response. Filamentous bacteriophage fd can display multiple copies of foreign peptides in the N-terminal region of its major coat protein pVIII, 2,700 copies of which make up the virus capsid. Here we show that fd virions displaying peptide RT2 (ILKEPVHGV), corresponding to residues 309-317 of the reverse transcriptase (RTase) of HIV-1, are able to prime a CTL response specific for this HIV-1 epitope in human cell lines. Successful priming also requires a T-helper epitope, pep23 (KDSWTVNDIQKLVGK), corresponding to residues 249-263 of HIV-1 RTase. Supplying this by displaying it on either the same or a separate bacteriophage virion led to activation of antigen-specific CD4+ T cells. Likewise, HLA-A2 transgenic mice immunized with bacteriophage virions displaying peptide RT2 were shown to mount an effective, specific anti-HIV-RT2 CTL response. This unexpected ability to elicit a designated cytolytic T-cell response, in addition to a B-cell response, has important implications for access to the class I major histocompatibility complex (MHC) loading compartment and the development of recombinant vaccines.

The role of the TolC family in protein transport and multidrug efflux. From stereochemical certainty to mechanistic hypothesis

Gram-negative bacteria are enveloped by a system of two membranes, and they use specialized multicomponent, energy-driven pumps to transport molecules directly across this double-layered partition from the cell interior to the extra-cellular environment. One component of these pumps is embedded in the outer-membrane, and the paradigm for its structure and function is the TolC protein from Escherichia coli. A common component of a wide variety of efflux pumps, TolC and its homologues are involved in the export of chemically diverse molecules ranging from large protein toxins, such as alpha-hemolysin, to small toxic compounds, such as antibiotics. TolC family members thus play important roles in conferring pathogenic bacteria with both virulence and multidrug resistance. These pumps assemble reversibly in a transient process that brings together TolC or its homologue, an inner-membrane-associated periplasmic component, an integral inner-membrane translocase and the substrate itself. TolC can associate in this fashion with a variety of different partners to participate in the transport of diverse substrates. We review here the structure and function of TolC and the other components of the efflux/transport pump.

Processing of filamentous bacteriophage virions in antigen-presenting cells targets both HLA class I and class II peptide loading compartments

Virions of filamentous bacteriophage fd are capable of displaying multiple copies of peptide epitopes and generating powerful immune responses to them. To investigate the antigen processing mechanisms in human B cell lines used as antigen presenting cells, the major coat protein (pVIII) in intact virions was fluorescently labeled, and its localization in various intracellular compartments was followed using confocal microscopy. We show that the virions were taken up and processed to yield peptides that reach both the major histocompatibility complex (MHC) class II compartment and the endoplasmic reticulum. Moreover, when exposed to bacteriophages displaying a cytotoxic T lymphocyte (CTL) epitope from the reverse transcriptase of human immunodeficiency virus type-1 (HIV-1), B cells were lysed by specific cytotoxic lymphocytes. This confirms that filamentous bacteriophage virions are capable of being taken up and processed efficiently by MHC class I and class II pathways, even in nonprofessional antigen presenting cells. These remarkable features explain, at least in part, the unexpected ability of virions displaying foreign T-cell epitopes to prime strong T-helper-dependent CTL responses. These findings have important implications for the development of peptide-based vaccines, using filamentous bacteriophage virions as scaffolds.

A xyloglucan-oligosaccharide-specific α-d-xylosidase or exo-oligoxyloglucan-α-xylohydrolase from germinated nasturtium (Tropaeolum majus L.) seeds : Purification, properties and its interaction with a xyloglucan-specific eneto-(1→4)-β-d-glucanase and other hydrolases during storage-xyloglucan mobilisation

The α-xylosidase which is involved in the postgerminative mobilisation of xyloglucan in nasturtium seed cotyledons has now been purified to apparent homogeneity by a facile procedure involving lectin affinity chromatography. The purified enzyme, a glycoprotein, moved as a single band (apparent molecular weight 85000) on sodium dodecyl sulphate-gel electrophoresis, whilst isoelectric focusing gave a number of enzymatically active protein bands spanning the range pI = 5.0 to 7.1 (maximum activity at pI = 6.1). The enzyme did not hydrolyse the simple α-xylosides p-nitrophenyl-α-d-xylopyranoside and woprimeverose (α-d-Xyl(1→6)-d-Glc), or polymeric tamarind-seed xyloglucan. It released xylose from a complex mixture of oligosaccharides produced by exhaustive hydrolysis of tamarind seed xyloglucan using the xyloglucan-specific endo-(1→4)-β-d-glucanase from germinated nasturtium seeds (M. Edwards et al. 1986, J. Biol. Chem., 261. 9489-9494). The three xyloglucan oligosaccharides of lowest molecular size were purified from this mixture and were shown by (1)H-nuclear magnetic resonance ((1)H-NMR) and enzymatic analysis to have the structures:

Detection of anti-p53 antibodies by ELISA using p53 synthetic or phage-displayed peptides

Anti-p53 antibodies have been detected in the sera of patients with various types of cancers. In this report, we describe the development of a new ELISA aimed at detecting anti-p53 antibodies using two peptides belonging to immunodominant epitopes of the p53 N-terminal region. We first tested the reactivity of the sera by an indirect ELISA using the peptides as a capture system. Then, the specificity of the reaction was confirmed by an inhibition assay. Two systems of peptide presentation, phage display and the streptavidin/biotin system, were evaluated. Using a panel of sera from cancer patients, both systems were found to be equally reliable, demonstrating that both peptide-based ELISAs can be used for the specific detection of anti-p53 antibodies. The presence of anti-p53 antibodies was associated with p53 alteration whether it be mutation or accumulation.

Substrate subsite recognition of the xyloglucan endo-transglycosylase or xyloglucan-specific endo-(1-->4)-beta-D-glucanase from the cotyledons of germinated nasturtium (Tropaeolum majus L.) seeds

We have investigated the substrate subsite recognition requirement of the xyloglucan endo-transglycosylase/xyloglucan-specific endo-(1-->4)-beta-D-glucanase (NXET) from the cotyledons of nasturtium seedlings. Seed xyloglucans are composed almost entirely of the Glc4 subunits XXXG, XLXG, XXLG and XLLG, where G represents an unsubstituted glucose residue, X a xylose-substituted glucose residue and L a galactosyl-xylose-substituted glucose residue. Thus in the xyloglucan sequence shown below, the xylose (Xyl) residues at the backbone glucose (Glc) residues numbered -3, -2, +2 and +3 may be galactose-substituted, and NXET cleaves between the unsubstituted glucose at -1 and the xylose-substituted glucose at +1, which never carries a galactosyl substituent. [formula: see text] We have isolated the xyloglucan oligosaccharides XXXGXXXG and XLLGXLLG from NXET digests of tamarind seed xyloglucan, have modified them enzymatically using a pure xyloglucan oligosaccharide-specific alpha-xylosidase from nasturtium seeds to give GXXGXXXG and GLLGXLLG, and have identified and compared the products of NXET action on XXXGXXXG, GXXGXXXG, XLLGXLLG and GLLGXLLG. We have also compared the molar proportions of XXXG, XLXG, XXLG and XLLG in native tamarind and nasturtium seed xyloglucans with those in NXET digests of these polysaccharides. Using these and existing data we have demonstrated that NXET action does not require xylose-substitution at glucose residues -4, -2, +1 and +3 and that xylose substitution at +2, is a requirement. There may also be a requirement for xylose substitution at -3. We have demonstrated also that galactosyl substitution of a xylose residue at +1 prevents, and at -2 modifies, chain-cleavage. A partial model for the minimum substrate binding requirement of NXET is proposed.

Melanocortin 1 receptor (MC1R) gene sequence variation and melanism in the gray (Sciurus carolinensis), fox (Sciurus niger), and red (Sciurus vulgaris) squirrel

Sequence variations in the melanocortin 1 receptor (MC1R) gene are associated with melanism in many different species of mammals, birds, and reptiles. The gray squirrel (Sciurus carolinensis), found in the British Isles, was introduced from North America in the late 19th century. Melanism in the British gray squirrel is associated with a 24-bp deletion in the MC1R. To investigate the origin of this mutation, we sequenced the MC1R of 95 individuals including 44 melanic gray squirrels from both the British Isles and North America. Melanic gray squirrels of both populations had the same 24-bp deletion associated with melanism. Given the significant deletion associated with melanism in the gray squirrel, we sequenced the MC1R of both wild-type and melanic fox squirrels (Sciurus niger) (9 individuals) and red squirrels (Sciurus vulgaris) (39 individuals). Unlike the gray squirrel, no association between sequence variation in the MC1R and melanism was found in these 2 species. We conclude that the melanic gray squirrel found in the British Isles originated from one or more introductions of melanic gray squirrels from North America. We also conclude that variations in the MC1R are not associated with melanism in the fox and red squirrels.

Action of a pure xyloglucan endo-transglycosylase (formerly called xyloglucan-specific endo-(1-->4)-beta-D-glucanase) from the cotyledons of germinated nasturtium seeds

The action on tamarind seed xyloglucan of the pure, xyloglucan-specific endo-(1-->4)-beta-D-glucanase from nasturtium (Tropaeolum majus L.) cotyledons has been compared with that of a pure endo-(1-->)-beta-D-glucanase ('cellulase') of fungal origin. The fungal enzyme hydrolysed the polysaccharide almost completely to a mixture of the four xyloglucan oligosaccharides: [formula: see text] Exhaustive digestion with the nasturtium enzyme gave the same four oligosaccharides plus large amounts of higher oligosaccharides and higher-polymeric material. Five of the product oligosaccharides (D, E, F, G, H) were purified and shown to be dimers of oligosaccharides A to C. D (glc8xyl6) had the structure A-->A, H (glc8xyl6 gal4) was C-->C, whereas E (glc8xyl6gal), F (glc8xyl6gal2) and G (glc8xyl6gal3) were mixtures of structural isomers with the appropriate composition. For example, F contained B2-->B2 (30%), A-->C (30%), C-->A (20%), B2-->B1 (15%) and others (about 5%). At moderate concentration (about 3 mM) oligosaccharides D to H were not further hydrolysed by the nasturtium enzyme, but underwent transglycosylation to give oligosaccharides from the group A, B, C, plus higher oligomeric structures. At lower substrate concentrations, hydrolysis was observed. Similarly, tamarind seed xyloglucan was hydrolysed to a greater extent at lower concentrations. It is concluded that the xyloglucan-specific nasturtium-seed endo-(1-->4)-beta-D-glucanase has a powerful xyloglucan-xyloglucan endo-transglycosylase activity in addition to its known xyloglucan-specific hydrolytic action. It would be more appropriately classified as a xyloglucan endo-transglycosylase. The action and specificity of the nasturtium enzyme are discussed in the context of xyloglucan metabolism in the cell walls of seeds and in other plant tissues.

Novel tissue remodelling roles for human recombinant erythropoietin

rHuEPO (recombinant human erythropoietin) is a haemopoietic growth factor and a primary regulator of erythropoiesis that is used for the treatment of chronic anaemia associated with RA (rheumatoid arthritis). Erythropoietin also appears to modulate a broad array of cellular processes, including progenitor stem-cell development, cellular integrity, angiogenesis and oxidative damage. These diverse activities suggest the exciting possibility of multiple roles for rHuEPO therapy in a variety of disorders other than RA, including cerebral ischaemia, myocardial infarction, chronic congestive heart failure and cancer. Thus it appears that rHuEPO may be a pleiotropic agent, capable of influencing tissue remodelling independently of its established erythropoietic role. Whereas these effects may be largely beneficial, dose-related side effects could have implications for the safe therapeutic use of rHuEPO and its illegal use as a performance-enhancing agent in endurance sports.

Membrane Association of the Short Transglutaminase Type 2 Splice Variant (TG2-S) Modulates Cisplatin Resistance in a Human Hepatocellular Carcinoma (HepG2) Cell Line

Hepatocellular carcinoma (HCC) is a heterogeneous malignancy with complex carcinogenesis. Although there has been significant progress in the treatment of HCC over the past decades, drug resistance to chemotherapy remains a major obstacle in its successful management. In this study, we were able to reduce chemoresistance in cisplatin-resistant HepG2 cells by either silencing the expression of transglutaminase type 2 (TG2) using siRNA or by the pre-treatment of cells with the TG2 enzyme inhibitor cystamine. Further analysis revealed that, whereas the full-length TG2 isoform (TG2-L) was almost completely cytoplasmic in its distribution, the majority of the short TG2 isoform (TG2-S) was membrane-associated in both parental and chemoresistant HepG2 cells. Following the induction of cisplatin toxicity in non-chemoresistant parental cells, TG2-S, together with cisplatin, quickly relocated to the cytosolic fraction. Conversely, no cytosolic relocalisation of TG2-S or nuclear accumulation cisplatin was observed, following the identical treatment of chemoresistant cells, where TG2-S remained predominantly membrane-associated. This suggests that the deficient subcellular relocalisation of TG2-S from membranous structures into the cytoplasm may limit the apoptic response to cisplatin toxicity in chemoresistant cells. Structural analysis of TG2 revealed the presence of binding motifs for interaction of TG2-S with the membrane scaffold protein LC3/LC3 homologue that could contribute to a novel mechanism of chemotherapeutic resistance in HepG2 cells.