Abstract
Polysaccharide extracts were obtained from chestnut bran (Castanea sativa), grape marc (Vitis vinifera) and apple marc (Malus spp.) and fractionated by size exclusion chromatography after endopolygalacturonase degradation. Compositional and linkage analyses by GC and GC-MS showed the characteristic rhamnogalacturonan structure with specific arabinan (apple marc) and type II arabinogalactan (chestnut bran, grape marc) side chains. Type II arabinogalactan rhamnogalacturonan from chestnut bran significantly stimulated the in vitro differentiation of human keratinocytes, giving evidence of a tight structure-function relationship. This molecule comprises short and ramified 3- and 3,6-β-d-galactan and 5- and 3,5-α-l-arabinan side chains, but also contains significant amounts of t‑Xyl and 4‑Xyl with a characteristic 2:1 ratio. Enzymatic hydrolysis of this polysaccharide produced fragments of lower molecular weight with unchanged xylose content which conserved the same ability to stimulate human keratinocyte differentiation. It could be then speculated that dimeric xylosyl-xylose and/or longer oligomeric xylose side chains attached to a galacturonan and closely associated to hairy rhamno-galacturonan domains are essential patterns that could determine the biological activity of pectins.
Highlights
Laboratoire de Chimie des Substances Naturelles (UPRES-EA 1069), Université de Limoges, Faculté des Sciences et Techniques, 123 rue A
The presence of 5- and 3,5-Ara and 3- and 3,6-Gal units in grape marc rhamnogalacturonans is characteristic of type II arabinogalactan side chains (AG-II); again, these data are in full agreement with earlier findings [15]
Fractionation of grape and apple marc crude extracts on Biogel P6 led to a significant decrease of their HSP27 stimulating power, polysaccharidic FI as well as oligosaccharidic FII subfractions derived from endoPG hydrolysis of chestnut bran rhamnogalacturonan crude extract, conserved the same level of activity
Summary
Laboratoire de Chimie des Substances Naturelles (UPRES-EA 1069), Université de Limoges, Faculté des Sciences et Techniques, 123 rue A. Except for chestnut bran extract, whose composition was dominated by Glc as a result of starch contamination, Rha, GalA, Ara and Gal were the characteristic monosaccharides units identified in the polysaccharidic fraction, confirming the typical rhamnogalacturonic nature of these extracts (Table 2).
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