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首页> 外文期刊>Biochemistry >Structural changes of the active site tunnel of Humicola insolens cellobiohydrolase, Cel6A, upon oligosaccharide binding.
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Structural changes of the active site tunnel of Humicola insolens cellobiohydrolase, Cel6A, upon oligosaccharide binding.

机译：寡糖结合后腐质霉腐殖质纤维二糖水解酶Cel6A活性位点通道的结构变化。

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摘要

The mechanisms of crystalline cellulose degradation by cellulases are of paramount importance for the exploitation of these enzymes in applied processes, such as biomass conversion. Cellulases have traditionally been classified into cellobiohydrolases, which are effective in the degradation of crystalline materials, and endoglucanases, which appear to act on "soluble" regions of the substrate. Humicola insolensCel6A (CBH II) is a cellobiohydrolase from glycoside hydrolase family 6 whose native structure has been determined at 1.9 A resolution [Varrot, A., Hastrup, S., Schulein, M., and Davies, G. J. (1999) Biochem. J. 337, 297-304]. Here we present the structure of the catalytic core domain of Humicola insolens cellobiohydrolase II Cel6A in complex with glucose/cellotetraose at 1.7 A resolution. Crystals of Cel6A, grown in the presence of cellobiose, reveal six binding subsites, with a single glucose moiety bound in the -2 subsite and cellotetraose in the +1 to +4 subsites. The complex structure is strongly supportive of the assignment of Asp 226 as the catalytic acid and consistent with proposals that Asp 405 acts as the catalytic base. The structure undergoes several conformational changes upon substrate binding, the most significant of which is a closing of the two active site loops (residues 174-196 and 397-435) with main-chain movements of up to 4.5 A observed. This complex not only defines the polysaccharide-enzyme interactions but also provides the first three-dimensional demonstration of conformational change in this class of enzymes.
机译：纤维素酶降解结晶纤维素的机制对于在应用过程（例如生物质转化）中利用这些酶至关重要。纤维素酶传统上被分为纤维二糖水解酶和内切葡聚糖酶，所述纤维二糖水解酶对晶体材料的降解有效，而内切葡聚糖酶似乎作用于底物的“可溶性”区域。腐质霉腐殖质Cel6A（CBH II）是来自糖苷水解酶家族6的纤维二糖水解酶，其天然结构已在1.9A分辨率下确定[Varrot，A.，Hastrup，S.，Schulein，M。，和Davies，G.J。（1999）Biochem.Acad.Sci.Sci.USA，87：2877-2。 [J.337，297-304]。在这里，我们提出了腐殖质腐殖质纤维二糖水解酶II Cel6A与葡萄糖/纤维四糖复合在1.7 A分辨率的催化核心结构域的结构。在纤维二糖存在下生长的Cel6A晶体揭示了六个结合亚位点，其中一个葡萄糖部分结合在-2亚位点中，而纤维四糖则结合在+1至+4亚位点中。复杂的结构强烈支持将Asp 226分配为催化酸，并与Asp 405用作催化碱的提议相一致。该结构在与底物结合后经历了几种构象变化，其中最重要的是两个活性位点环（残基174-196和397-435）的闭合，主链运动高达4.5A。这种复合物不仅定义了多糖-酶的相互作用，而且还提供了这类酶构象变化的第一个三维证明。

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