Awanthi Mahanama Geegana Gamage, Umosa Manatsu, Yuguchi Yoshiaki, Oku Hirosuke, Kitahara Kanefumi, Ito Michihiro, Tanaka Atsuko, Konishi Teruko
United Graduate School of Agricultural Sciences, Kagoshima University, 1-21-24 Korimoto, Kagoshima-shi, Kagoshima, 890-0065, Japan.
Department of Bioscience and Biotechnology, Faculty of Agriculture, University of the Ryukyus, 1 Senbaru, Nishihara-cho, Okinawa, 903-0213, Japan.
Carbohydr Res. 2023 Jan;523:108722. doi: 10.1016/j.carres.2022.108722. Epub 2022 Nov 16.
Brown algae contain a polysaccharide-rich cell wall, mainly composed of alginate and fucoidan which have been extensively studied for their individual structure and bioactivities. Particularly, the cell wall of Cladosiphon okamuranus is rich in fucoidan rather than alginate. However, little is known about its arrangement or interlinking with other polysaccharides such as cellulose in the cell wall. To determine its structure in detail, the cell wall was sequentially fractionated into five fractions: hot water (HW), ammonium oxalate, hemicellulose-I (HC-I), HC-II, and cellulose. Almost 80% of the total cell wall recovered from alcohol insoluble residue in C. okamuranus consisted of HW and HC-I, which mainly contained fucoidan composed of fucose, glucuronic acid, and sulfate in molar ratios of 1.0:0.3:0.9 and 1.0:0.2:0.3, respectively. Methylation analysis revealed that fucoidan in HW and HC-I structurally differed in terms of content of sulfate, and sugar residue which was 1,4-linked xylose and 1,4-linked fucose. Small angle X-ray scattering measurements also showed distinct conformational differences between HW and HC-I. These structural heterogeneities of fucoidan may be related to their localization, and fucoidan in HC-I may be involved in reinforcing cell wall structure by cross-linking to cellulose.
褐藻含有富含多糖的细胞壁，主要由藻酸盐和岩藻聚糖组成，人们对它们各自的结构和生物活性进行了广泛研究。特别是，冈村枝管藻的细胞壁富含岩藻聚糖而非藻酸盐。然而，关于其在细胞壁中的排列方式或与其他多糖（如纤维素）的交联情况却知之甚少。为了详细确定其结构，将细胞壁依次分离为五个组分：热水提取物（HW）、草酸铵提取物、半纤维素-I（HC-I）、HC-II和纤维素。从冈村枝管藻的醇不溶性残渣中回收的总细胞壁中，近80%由HW和HC-I组成，它们主要含有岩藻聚糖，其岩藻糖、葡萄糖醛酸和硫酸盐的摩尔比分别为1.0:0.3:0.9和1.0:0.2:0.3。甲基化分析表明，HW和HC-I中的岩藻聚糖在硫酸盐含量以及糖残基（1,4-连接的木糖和1,4-连接的岩藻糖）方面结构不同。小角X射线散射测量也显示HW和HC-I之间存在明显的构象差异。岩藻聚糖的这些结构异质性可能与其定位有关，并且HC-I中的岩藻聚糖可能通过与纤维素交联参与增强细胞壁结构。
