Thiamin pyrophosphokinase catalyzes the pyrophosphorylation of thiamin to thiamin pyrophosphate in the presence of ATP and Mgtt The kinetic properties of human thiamin pyrophosphokinase (hTPK1) were investigated using purified histidine-tagged recombinant protein. The plots of the initial velocity against MgATP concentrations gave a sigmoidal character when Mg2+/ATP was maintained at 1. However, the addition of an excess amount of Mg2+ resulted in the restoration of activity at lower concentrations of MgATP A steady-state kinetics study led us to conclude that the kinase reaction obeys a ping-ong mechanism. Site-directed mutagenesis was also performed on hTPK1 to examine the contributions of eight strictly conserved residues in thiamin pyrophosphokinase on the kinetic properties. Mutations D71N, D73N, and D100N reduced kcat markedly, indicating that these aspartic acids play a crucial role in carrying out the catalytic process of hTPK1. A selective decrease in the kcat/Kmthiamin value was observed in the D133N mutant, whereas the kcat/KmATV values of T99A and R131G were significantly decreased. Interestingly, the replacement of Gln-96 with Glu caused an increase in the kcat/Kmthiamin value (3.53-fold of the wild-type). It was therefore suggested that the residues Gln-96, Thr-99, Arg-131, and Asp-133 are conserved as functionally significant components for substrate recognition in thiamin pyrophosphokinase.
硫胺素焦
磷激酶在
ATP 和 Mgtt 存在下催化
硫胺素焦磷酸化为
硫胺素焦磷酸 利用纯化的组
氨酸标记
重组蛋白研究了人
硫胺素焦
磷激酶(hTPK1)的动力学特性。当 Mg2+/
ATP 浓度保持为 1 时,初始速度与 Mg
ATP 浓度的关系图呈现半规线性关系。我们还对 hTPK1 进行了定点突变,以研究
硫胺素焦
磷激酶中八个严格保守的残基对其动力学特性的贡献。突变 D71N、D73N 和 D100N 会明显降低 kcat,表明这些
天冬氨酸在 hTPK1 的催化过程中起着关键作用。在 D133N 突变体中观察到了 kcat/Kmthiamin 值的选择性降低,而 T99A 和 R131G 的 kcat/KmATV 值也显著降低。有趣的是,用 Glu 取代 Gln-96 会导致 kcat/Kmthiamin 值增加(野生型的 3.53 倍)。因此,Gln-96、Thr-99、Arg-131 和 Asp-133 残基是
硫胺素焦
磷激酶中具有重要功能的底物识别成分。