Structure elucidation of an immunostimulatory arabinoxylan-type polysaccharide prepared from young barley leaves (Hordeum vulgare L.)

Abstract

We recently isolated an immunostimulating polysaccharide (BLE-P-I), which possesses a large proportion of arabinoxylan, from young barley leaves. In the present study, to elucidate the structural details of BLE-P-I, it was fractionated into enzyme-resistant fraction (BLE-P-I-X1) and arabinoxylan-rich oligosaccharide fraction (BLE-P-I-X2) after endo-xylanase hydrolysis. Commercial wheat arabinoxylan was also fractionated into WAX-XI and WAX-X2 after the same treatment. BLE-P-I-X2 consisted of arabinose and xylose, including 11 types of neutral glycosidic linkages, whereas WAX-X2 had less, with 6 types of linkages. Mass spectrometric results indicated that WAX-X2 was composed of a xylan backbone bearing only arabinose. In contrast, BLE-P-I-X2 consisted of a xylan backbone with acetate, arabinose, galactose, glucuronic acid, and 4-0-methylglucuronic acid, resembling structural characteristics as glucuronoarabinoxylan. Macrophage-stimulatory activity showed that BLE-P-I-X2 has a role in the expression of the activity. These results indicate that the structural complexity of arabinoxylan seems to be responsible for the immunomodulatory activity in barley leaf. (C) 2016 Elsevier Ltd. All rights reserved.