Moreira L R S, Filho E X F
Departamento de Biologia Celular, Laboratório de Enzimologia, Universidade de Brasília, CEP 70910-900 Brasília, DF, Brazil.
Appl Microbiol Biotechnol. 2008 May;79(2):165-78. doi: 10.1007/s00253-008-1423-4.
Hemicellulose is a complex group of heterogeneous polymers and represents one of the major sources of renewable organic matter. Mannan is one of the major constituent groups of hemicellulose in the wall of higher plants. It comprises linear or branched polymers derived from sugars such as D-mannose, D-galactose, and D-glucose. The principal component of softwood hemicellulose is glucomannan. Structural studies revealed that the galactosyl side chain hydrogen interacts to the mannan backbone intramolecularly and provides structural stability. Differences in the distribution of D-galactosyl units along the mannan structure are found in galactomannans from different sources. Acetyl groups were identified and distributed irregularly in glucomannan. Some of the mannosyl units of galactoglucomannan are partially substituted by O-acetyl groups. Some unusual structures are found in the mannan family from seaweed, showing a complex system of sulfated structure. Endohydrolases and exohydrolases are involved in the breakdown of the mannan backbone to oligosaccharides or fermentable sugars. The main-chain mannan-degrading enzymes include beta-mannanase, beta-glucosidase, and beta-mannosidase. Additional enzymes such as acetyl mannan esterase and alpha-galactosidase are required to remove side-chain substituents that are attached at various points on mannan, creating more sites for subsequent enzymatic hydrolysis. Mannan-degrading enzymes have found applications in the pharmaceutical, food, feed, and pulp and paper industries. This review reports the structure of mannans and some biochemical properties and applications of mannan-degrading enzymes.
半纤维素是一组复杂的异质聚合物，是可再生有机物质的主要来源之一。甘露聚糖是高等植物细胞壁中半纤维素的主要组成基团之一。它由源自D-甘露糖、D-半乳糖和D-葡萄糖等糖类的线性或支链聚合物组成。软木半纤维素的主要成分是葡甘露聚糖。结构研究表明，半乳糖基侧链氢与甘露聚糖主链发生分子内相互作用并提供结构稳定性。在不同来源的半乳甘露聚糖中，沿着甘露聚糖结构的D-半乳糖基单元分布存在差异。乙酰基在葡甘露聚糖中被鉴定出来且分布不规则。半乳葡甘露聚糖的一些甘露糖基单元被O-乙酰基部分取代。在海藻的甘露聚糖家族中发现了一些不寻常的结构，呈现出一个复杂的硫酸化结构系统。内切水解酶和外切水解酶参与将甘露聚糖主链分解为寡糖或可发酵糖。主链甘露聚糖降解酶包括β-甘露聚糖酶、β-葡萄糖苷酶和β-甘露糖苷酶。还需要诸如乙酰甘露聚糖酯酶和α-半乳糖苷酶等其他酶来去除连接在甘露聚糖不同位点上的侧链取代基，为后续的酶促水解创造更多位点。甘露聚糖降解酶已在制药、食品、饲料以及纸浆和造纸工业中得到应用。本综述报道了甘露聚糖的结构以及甘露聚糖降解酶的一些生化特性和应用。
