Hefei National Laboratory for Physical Sciences at Microscale, and School of Life Sciences, University of Science and Technology of China, Hefei, Anhui 230027, People's Republic of China.
EMBO Rep. 2009 Dec;10(12):1320-6. doi: 10.1038/embor.2009.216. Epub 2009 Oct 23.
Glutathione-S-transferases (GSTs) are ubiquitous detoxification enzymes that catalyse the conjugation of electrophilic substrates to glutathione. Here, we present the crystal structures of Gtt2, a GST of Saccharomyces cerevisiae, in apo and two ligand-bound forms, at 2.23 A, 2.20 A and 2.10 A, respectively. Although Gtt2 has the overall structure of a GST, the absence of the classic catalytic essential residues--tyrosine, serine and cysteine--distinguishes it from all other cytosolic GSTs of known structure. Site-directed mutagenesis in combination with activity assays showed that instead of the classic catalytic residues, a water molecule stabilized by Ser129 and His123 acts as the deprotonator of the glutathione sulphur atom. Furthermore, only glycine and alanine are allowed at the amino-terminus of helix-alpha1 because of stereo-hindrance. Taken together, these results show that yeast Gtt2 is a novel atypical type of cytosolic GST.
谷胱甘肽-S-转移酶（GSTs）是广泛存在的解毒酶，可催化亲电底物与谷胱甘肽的结合。在这里，我们展示了酿酒酵母 GST Gtt2 的晶体结构，分别在 apo 和两种配体结合形式下达到 2.23Å、2.20Å 和 2.10Å 的分辨率。尽管 Gtt2 具有 GST 的整体结构，但缺乏经典的催化必需残基——酪氨酸、丝氨酸和半胱氨酸——将其与所有其他已知结构的胞质 GST 区分开来。定点突变与活性测定相结合的结果表明，不是经典的催化残基，而是由 Ser129 和 His123 稳定的水分子充当谷胱甘肽硫原子的去质子化剂。此外，由于空间位阻，仅允许在α1 螺旋的氨基末端使用甘氨酸和丙氨酸。总之，这些结果表明酵母 Gtt2 是一种新型的非典型胞质 GST。
