Boraston Alisdair B, Revett Timothy J, Boraston Catherine M, Nurizzo Didier, Davies Gideon J
Department of Chemistry, University of York, Heslington, York YO10 5YW, United Kingdom.
Structure. 2003 Jun;11(6):665-75. doi: 10.1016/s0969-2126(03)00100-x.
The C-terminal 176 amino acids of a Thermotoga maritima mannanase (Man5) constitute a carbohydrate binding module (CBM) that has been classified into CBM family 27. The isolated CBM27 domain, named TmCBM27, binds tightly (K(a)s 10(5)-10(6) M(-1)) to beta-1, 4-mannooligosaccharides, carob galactomannan, and konjac glucomannan, but not to cellulose (insoluble and soluble) or soluble birchwood xylan. The X-ray crystal structures of native TmCBM27, a TmCBM27-mannohexaose complex, and a TmCBM27-6(3),6(4)-alpha-D-galactosyl-mannopentaose complex at 2.0 A, 1.6 A, and 1.35 A, respectively, reveal the basis of TmCBM27's specificity for mannans. In particular, the latter complex, which is the first structure of a CBM in complex with a branched plant cell wall polysaccharide, illustrates how the architecture of the binding site can influence the recognition of naturally substituted polysaccharides.
嗜热栖热菌甘露聚糖酶（Man5）的C末端176个氨基酸构成了一个碳水化合物结合模块（CBM），该模块已被归类为CBM家族27。分离出的CBM27结构域，命名为TmCBM27，与β-1,4-甘露寡糖、角豆树半乳甘露聚糖和魔芋葡甘露聚糖紧密结合（解离常数Ka为10⁵ - 10⁶ M⁻¹），但不与纤维素（不溶性和可溶性）或可溶性桦木木聚糖结合。天然TmCBM27、TmCBM27-甘露六糖复合物以及TmCBM27-6(3),6(4)-α-D-半乳糖基-甘露五糖复合物的X射线晶体结构分别在2.0 Å、1.6 Å和1.35 Å分辨率下解析出来，揭示了TmCBM27对甘露聚糖具有特异性的基础。特别是，后一种复合物是CBM与分支植物细胞壁多糖形成的复合物的首个结构，它阐明了结合位点的结构如何影响对天然取代多糖的识别。
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