Center for Biocrystallographic Research, Institute of Bioorganic Chemistry, Polish Academy of Sciences, Poznań, Poland.
Department of Molecular Physiology and Neurobiology, Wroclaw University, Wrocław, Poland.
Acta Biochim Pol. 2021 Jan 27;68(1):5-14. doi: 10.18388/abp.2020_5554.
Muscle fructose-1,6-bisphosphatase (FBPase), which catalyzes the hydrolysis of fructose-1,6-bisphosphate (F1,6BP) to fructose-6-phosphate (F6P) and inorganic phosphate, regulates glucose homeostasis by controlling the glyconeogenic pathway. FBPase requires divalent cations, such as Mg2+, Mn2+, or Zn2+, for its catalytic activity; however, calcium ions inhibit the muscle isoform of FBPase by interrupting the movement of the catalytic loop. It has been shown that residue E69 in this loop plays a key role in the sensitivity of muscle FBPase towards calcium ions. The study presented here is based on five crystal structures of wild-type human muscle FBPase and its E69Q mutant in complexes with the substrate and product of the enzymatic reaction, namely F1,6BP and F6P. The ligands are bound in the active site of the studied proteins in the same manner and have excellent definition in the electron density maps. In all studied crystals, the homotetrameric enzyme assumes the same cruciform quaternary structure, with the κ angle, which describes the orientation of the upper dimer with respect to the lower dimer, of -85o. This unusual quaternary arrangement of the subunits, characteristic of the R-state of muscle FBPase, is also observed in solution by small-angle X-ray scattering (SAXS).
肌肉果糖-1,6-二磷酸酶（FBPase）可催化果糖-1,6-二磷酸（F1,6BP）水解为果糖-6-磷酸（F6P）和无机磷酸，通过控制糖异生途径来调节葡萄糖稳态。FBPase 的催化活性需要二价阳离子，如 Mg2+、Mn2+或 Zn2+；然而，钙离子通过中断催化环的运动来抑制肌肉 FBPase 的同工酶。已经表明，该环中的残基 E69 在肌肉 FBPase 对钙离子的敏感性中起着关键作用。本研究基于野生型人肌肉 FBPase 及其与酶促反应的底物和产物（即 F1,6BP 和 F6P）结合的 E69Q 突变体的五个晶体结构。配体以相同的方式结合在研究蛋白的活性部位，并且在电子密度图中具有极好的定义。在所有研究的晶体中，同源四聚体酶采用相同的十字形四级结构，κ 角描述了上二聚体相对于下二聚体的取向，为-85o。这种亚基的异常四级排列，是肌肉 FBPase 的 R 状态的特征，也通过小角 X 射线散射（SAXS）在溶液中观察到。
