Donald Danforth Plant Science Center, St. Louis, MO 63132, USA.
Structure. 2010 Feb 10;18(2):200-15. doi: 10.1016/j.str.2009.12.010.
SusG is an alpha-amylase and part of a large protein complex on the outer surface of the bacterial cell and plays a major role in carbohydrate acquisition by the animal gut microbiota. Presented here, the atomic structure of SusG has an unusual extended, bilobed structure composed of amylase at one end and an unprecedented internal carbohydrate-binding motif at the other. Structural studies further demonstrate that the carbohydrate-binding motif binds maltooligosaccharide distal to, and on the opposite side of, the amylase catalytic site. SusG has an additional starch-binding site on the amylase domain immediately adjacent to the active cleft. Mutagenesis analysis demonstrates that these two additional starch-binding sites appear to play a role in catabolism of insoluble starch. However, elimination of these sites has only a limited effect, suggesting that they may have a more important role in product exchange with other Sus components.
SusG 是一种α-淀粉酶，属于细菌细胞外表面的大型蛋白复合物的一部分，在动物肠道微生物群获取碳水化合物方面发挥着主要作用。本文介绍了 SusG 的原子结构，它具有不寻常的伸展双叶结构，一端是淀粉酶，另一端是前所未有的内部碳水化合物结合基序。结构研究进一步表明，碳水化合物结合基序结合的麦芽寡糖位于淀粉酶催化位点的远端和对面。SusG 在淀粉酶结构域上还有一个紧邻活性裂缝的额外淀粉结合位点。突变分析表明，这两个额外的淀粉结合位点似乎在不溶性淀粉的分解代谢中发挥作用。然而，消除这些位点的作用有限，这表明它们可能在与其他 Sus 成分的产物交换中发挥更重要的作用。
