Lahaye Marc, Rondeau-Mouro Corinne, Deniaud Estelle, Buléon Alain
INRA-Unité de Recherches sur les Polysaccharides, leurs Organisations et Interactions, BP 71627, F-44316 Nantes, France.
Carbohydr Res. 2003 Jul 22;338(15):1559-69. doi: 10.1016/s0008-6215(03)00241-6.
The chemical structure and interactions of the cell wall polysaccharides from the red edible seaweed Palmaria palmata were studied by liquid-like magic-angle-spinning (MAS) and cross-polarization MAS (CPMAS) solid-state 13C NMR spectroscopy. The liquid-like MAS and CPMAS 13C NMR spectra of the rehydrated algal powder revealed the presence of beta-(1-->4)/beta-(1-->3)-linked D-xylan with chemical shifts close to those observed in the solution 13C NMR spectrum of the polysaccharide. Observation of mix-linked xylan in the liquid-like MAS 13C NMR spectrum indicated that part of this cell wall polysaccharide is loosely held in the alga. The CPMAS NMR spectrum of the dry algal powder alcohol insoluble residue (AIR) showed broad peaks most of which corresponded to the mix-linked xylan. Hydration of AIR induced a marked increase in the signal resolution also in the CPMAS NMR spectra together with a shift of the C-3 and C-4 signals of the (1-->3)- and (1-->4)-linked xylose, respectively. Such modifications were present in the spectrum of hydrated (1-->3)-linked xylan from the green seaweed Caulerpa taxifolia and absent in that of (1-->4)-linked xylan from P. palmata. This result emphasizes the important role of (1-->3) linkages on the mix-linked xylan hydration-induced conformational rearrangement. The mix-linked xylan signals were observed in the CPMAS NMR spectrum of hydrated residues obtained after extensive extractions by NaOH or strong chaotropic solutions indicating strong hydrogen bonds or covalent linkages. T(1 rho) relaxations were measured close or above 10 ms for the mix-linked xylan in the dry and hydrated state in AIR and indicated that the overall xylan chains likely remain rigid. Rehydration of the mix-linked xylan lead to a decrease in the motion of protons bounded to the C-1 and C-4 carbons of the (1-->4)-linked xylose supporting the re-organization of the xylan chains under hydration involving junction-zones held by hydrogen bonds between adjacent (1-->4)-linked xylose blocks. The CPMAS NMR spectrum of both dry and rehydrated residues obtained after NaOH and HCl extractions demonstrated the presence of cellulose and (1-->4)-linked xylans. The structures of the different polysaccharides are discussed in relation to their interactions and putative functions on the cell wall mechanical properties in P. palmata.
采用类液体魔角旋转（MAS）和交叉极化MAS（CPMAS）固态13C核磁共振波谱法研究了可食用红色海藻掌状红皮藻细胞壁多糖的化学结构及其相互作用。再水化藻粉的类液体MAS和CPMAS 13C核磁共振波谱显示存在β-(1→4)/β-(1→3)连接的D-木聚糖，其化学位移与多糖溶液13C核磁共振波谱中观察到的化学位移相近。在类液体MAS 13C核磁共振波谱中观察到混合连接的木聚糖，表明这种细胞壁多糖的一部分在藻类中以松散的形式存在。干燥藻粉醇不溶物（AIR）的CPMAS核磁共振波谱显示出宽峰，其中大部分对应于混合连接的木聚糖。AIR的水化还导致CPMAS核磁共振波谱中的信号分辨率显著提高，同时(1→3)-和(1→4)-连接木糖的C-3和C-4信号分别发生位移。这种修饰存在于绿藻杉叶蕨藻的水化(1→3)-连接木聚糖的光谱中，而不存在于掌状红皮藻的(1→4)-连接木聚糖的光谱中。这一结果强调了(1→3)连接在混合连接木聚糖水化诱导的构象重排中的重要作用。在通过NaOH或强离液剂溶液进行广泛提取后获得的水合残渣的CPMAS核磁共振波谱中观察到混合连接的木聚糖信号，表明存在强氢键或共价键。在AIR中，对干燥和水合状态下的混合连接木聚糖测量的T(1ρ)弛豫时间接近或高于10 ms，表明木聚糖链整体可能保持刚性。混合连接木聚糖的再水化导致与(1→4)-连接木糖的C-1和C-4碳结合的质子运动减少，这支持了水合作用下木聚糖链的重新组织，涉及相邻(1→4)-连接木糖块之间通过氢键保持的连接区。NaOH和HCl提取后获得的干燥和再水化残渣的CPMAS核磁共振波谱都证明了纤维素和(1→4)-连接木聚糖的存在。讨论了不同多糖的结构与其在掌状红皮藻细胞壁力学性质方面的相互作用和假定功能的关系。
