Bott Richard, Saldajeno Mae, Cuevas William, Ward Donald, Scheffers Martijn, Aehle Wolfgang, Karkehabadi Saeid, Sandgren Mats, Hansson Henrik
Genencor-A Danisco Division, 925 Page Mill Road, Palo Alto, California 94304, USA.
Biochemistry. 2008 May 27;47(21):5746-54. doi: 10.1021/bi702413k. Epub 2008 May 6.
The three-dimensional structure of a complete Hypocrea jecorina glucoamylase has been determined at 1.8 A resolution. The presented structure model includes the catalytic and starch binding domains and traces the course of the 37-residue linker segment. While the structures of other fungal and yeast glucoamylase catalytic and starch binding domains have been determined separately, this is the first intact structure that allows visualization of the juxtaposition of the starch binding domain relative to the catalytic domain. The detailed interactions we see between the catalytic and starch binding domains are confirmed in a second independent structure determination of the enzyme in a second crystal form. This second structure model exhibits an identical conformation compared to the first structure model, which suggests that the H. jecorina glucoamylase structure we report is independent of crystal lattice contact restraints and represents the three-dimensional structure found in solution. The proposed starch binding regions for the starch binding domain are aligned with the catalytic domain in the three-dimensional structure in a manner that supports the hypothesis that the starch binding domain serves to target the glucoamylase at sites where the starch granular matrix is disrupted and where the enzyme might most effectively function.
已在1.8埃分辨率下确定了完整的嗜热栖热放线菌葡糖淀粉酶的三维结构。所呈现的结构模型包括催化结构域和淀粉结合结构域，并描绘了37个残基的连接片段的走向。虽然其他真菌和酵母葡糖淀粉酶的催化结构域和淀粉结合结构域的结构已分别确定，但这是第一个完整的结构，能够可视化淀粉结合结构域相对于催化结构域的并列情况。我们在催化结构域和淀粉结合结构域之间看到的详细相互作用，在该酶以第二种晶体形式进行的第二次独立结构测定中得到了证实。与第一个结构模型相比，第二个结构模型呈现出相同的构象，这表明我们报道的嗜热栖热放线菌葡糖淀粉酶结构独立于晶格接触限制，代表了溶液中发现的三维结构。淀粉结合结构域的拟淀粉结合区域在三维结构中与催化结构域对齐，这种方式支持了以下假设：淀粉结合结构域用于将葡糖淀粉酶靶向淀粉颗粒基质被破坏且酶可能最有效发挥作用的位点。
