The selective hydrolysis of tamarind seed xyloglucan (tamarind gum) using enzymes isolated from germinated nasturtium (Tropaeolum majus L.) cotyledons

"The selective hydrolysis of tamarind seed xyloglucan (Tamarind gum) using enzymes isolated from germinated nasturtium (Tropaeobun majus L.) seeds". Background. Tamarind seed xyloglucan is a storage cell wall polysaccharide which consists of a rigid cellulose-like backbone of (l-»4)-B-D-linked glucopyranosyl units carrying both D-xylopyranosyl residues and D-galactopyranosyl-B-(l-»2)-xylopyranosyl residues. The xylosyl residue is linked a-(l-»6) on to the main glucan chain. The xyloglucan polysaccharide of the primary cell wall of growing plants has very similar composition and structure with the only exception that some terminal galactosyl residues carry L-fucosyl substituents attached a-(l-»2) (Fry, 1989; Hayashi, 1989). Mobilization of storage xyloglucan following germination in Tropaeolum is brought about by the synergistic action of at least four enzymes, namelyendo-(l-»4)-B-D-glucanase,fi-galactosidase,a-xylosidaseandB-glucosidase (Edwards et al., 1985). The aims of the project were the purification and characterization of xyloglucan-specific hydrolases from germinated nasturtium cotyledons. Results and discussion. (A) The enzyme a-xylosidase was purified to homogeneity from germinated nasturtium cotyledons and the molecular properties were investigated. The enzyme is a glycoprotein (approx. Mr 85000, on SDS-PAGE) able to remove a single unsubstituted xylosyl residue attached to the backbone glucose at the nonreducing end of the xyloglucan oligosaccharide molecule (Fanutti et al., 1991). (B) The nasturtium endoglucanase (Edwards et al., 1986) was shown to be a novel type of transferase (xyloglucan emfo-transferase) able to catalyze the transglycosylation of xyloglucan molecules (Fanutti et al., 1993). Enzymes with the same specificity of the nasturtium endoglucanase have been correlated with primary cell wall elongation (Albersheim, 1976). (C) The nasturtium B-galactosidase (Edwards et al., 1988) catalyzes the selective removal of galactose residues from polymeric xyloglucan as well as xyloglucan oligosaccharides (Edwards et al., 1988). The rheological properties of modified xyloglucan were studied. Galactose-removal led to increased chain-chain interactions, and these were enhanced in the presence of Na2 SO4. Galactose residues at different positions in xyloglucan oligosaccharides were hydrolysed at different rates. References. Albersheim P. (1976), Plant Biochemistry 3rd Ed. Bonner and Varner, Academic Press, de Silva J., Jarman CD., Stronach M., Arrowsmith D., Smith C, Sidebottom C, Reid J.S.G. (1993), Plant J. 1, 701-711. Edwards M,. Dea I.C.M., Bulpin P.V., Reid J.S.G. (1985), Planta 163, 133-140. Edwards M., Dea I.C.M., Bulpin P.V., Reid J.S.G. (1986), J. Biol. Chem. 261, 9489-9494. Edwards M., Dea I.C.M., Bulpin P.V., Reid J.S.G. (1988) J. Biol. Chem. 263, 4333-4337. Fanutti C., Gidley M.J., Reid J.S.G. (1991), Planta 184, 137-147. Fanutti C, Gidley M.J., Reid J.S.G. (1993), The Plant J. 3, 691-700. Fry S.C. (1989), J. Exp. Bot. 40, 1-11. Hayashi T. (1989), Annu. Rev. Plant Physiol. Plant Mol. Biol.40, 139-168

Agouti signalling protein is an inverse agonist to the wildtype and agonist to the melanic variant of the melanocortin-1 receptor in the grey squirrel (Sciurus carolinensis)

The melanocortin-1 receptor (MC1R) is a key regulator of mammalian pigmentation. Melanism in the grey squirrel is associated with an eight amino acid deletion in the mutant melanocortin-1 receptor with 24 base pair deletion (MC1RΔ24) variant. We demonstrate that the MC1RΔ24 exhibits a higher basal activity than the wildtype MC1R (MC1R-wt). We demonstrate that agouti signalling protein (ASIP) is an inverse agonist to the MC1R-wt but is an agonist to the MC1RΔ24. We conclude that the deletion in the MC1RΔ24 leads to a receptor with a high basal activity which is further activated by ASIP. This is the first report of ASIP acting as an agonist to MC1R

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 recognition requirement transglycosylase/xyloglucan-specific endo-(1 --> 4)-beta-D-glucanase (NXET) from the cotyledons of nasturtium seedlings. Seed xyloglucans are composed almost entirely of the Glc, 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

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</p

Alleles of the melanocortin 1 receptor

DNA sequences of the MC1R genes of sciurus carolinensis, niger and vulgari

Data from: 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