Department of Chemistry and Biochemistry, James Madison University, 901 Carrier Drive, MSC 4501, Harrisonburg, VA 22807, USA.
Department of Biology, James Madison University, 951 Carrier Drive, MSC 7801, Harrisonburg, VA 22807, USA.
Acta Crystallogr D Struct Biol. 2020 Apr 1;76(Pt 4):357-365. doi: 10.1107/S2059798320002016. Epub 2020 Mar 25.
Starch is a key energy-storage molecule in plants that requires controlled synthesis and breakdown for effective plant growth. β-Amylases (BAMs) hydrolyze starch into maltose to help to meet the metabolic needs of the plant. In the model plant Arabidopsis thaliana there are nine BAMs, which have apparently distinct functional and domain structures, although the functions of only a few of the BAMs are known and there are no 3D structures of BAMs from this organism. Recently, AtBAM2 was proposed to form a tetramer based on chromatography and activity assays of mutants; however, there was no direct observation of this tetramer. Here, small-angle X-ray scattering data were collected from AtBAM2 and its N-terminal truncations to describe the structure and assembly of the tetramer. Comparison of the scattering of the AtBAM2 tetramer with data collected from sweet potato (Ipomoea batatas) BAM5, which is also reported to form a tetramer, showed there were differences in the overall assembly. Analysis of the N-terminal truncations of AtBAM2 identified a loop sequence found only in BAM2 orthologs that appears to be critical for AtBAM2 tetramer assembly as well as for activity.
淀粉是植物中一种重要的储能分子，为了有效促进植物生长，需要对其进行合成和分解的控制。β-淀粉酶（BAMs）将淀粉水解为麦芽糖，以帮助满足植物的代谢需求。在模式植物拟南芥中，有 9 种 BAMs，它们显然具有不同的功能和结构域，但只有少数几种 BAMs 的功能已知，并且该生物体没有 BAMs 的 3D 结构。最近，根据突变体的色谱和活性分析，提出 AtBAM2 形成四聚体；然而，并没有直接观察到这种四聚体。在这里，从小角度 X 射线散射数据收集 AtBAM2 及其 N 端截短体来描述四聚体的结构和组装。AtBAM2 四聚体的散射与从甘薯（Ipomoea batatas）BAM5 收集的数据进行比较，甘薯 BAM5 也被报道形成四聚体，表明整体组装存在差异。对 AtBAM2 的 N 端截短体的分析确定了一个仅在 BAM2 同源物中发现的环序列，该序列似乎对 AtBAM2 四聚体组装以及活性至关重要。
