Department of Chemistry, University of Eastern Finland, P.O. Box 111, FIN-80101 Joensuu, Finland.
J Struct Biol. 2011 Apr;174(1):156-63. doi: 10.1016/j.jsb.2010.11.024. Epub 2010 Dec 3.
We have determined the crystal structure of Trichoderma reesei (Hypocrea jecorina) β-galactosidase (Tr-β-gal) at a 1.2Å resolution and its complex structures with galactose, IPTG and PETG at 1.5, 1.75 and 1.4Å resolutions, respectively. Tr-β-gal is a potential enzyme for lactose hydrolysis in the dairy industry and belongs to family 35 of the glycoside hydrolases (GH-35). The high resolution crystal structures of this six-domain enzyme revealed interesting features about the structure of Tr-β-gal. We discovered conformational changes in the two loop regions in the active site, implicating a conformational selection-mechanism for the enzyme. In addition, the Glu200, an acid/base catalyst showed two different conformations which undoubtedly affect the pK(a) value of this residue and the catalytic mechanism. The electron density showed extensive glycosylation, suggesting a structure stabilizing role for glycans. The longest glycan showed an electron density that extends to the eighth monosaccharide unit in the extended chain. The Tr-β-gal structure also showed a well-ordered structure for a unique octaserine motif on the surface loop of the fifth domain.
我们解析了里氏木霉（Hypocrea jecorina）β-半乳糖苷酶（Tr-β-gal）的晶体结构，分辨率为 1.2Å，以及其与半乳糖、IPTG 和 PETG 的复合物结构，分辨率分别为 1.5Å、1.75Å 和 1.4Å。Tr-β-gal 是乳品工业中潜在的乳糖水解酶，属于糖苷水解酶家族 35（GH-35）。该六结构域酶的高分辨率晶体结构揭示了 Tr-β-gal 结构的一些有趣特征。我们发现活性位点中两个环区的构象发生变化，暗示该酶的构象选择机制。此外，作为酸/碱催化剂的Glu200 显示出两种不同的构象，这无疑会影响该残基的 pK(a) 值和催化机制。电子密度显示广泛的糖基化，表明聚糖具有结构稳定作用。最长的聚糖显示出延伸链中第八个单糖单元的电子密度。Tr-β-gal 结构还在第五结构域表面环上的独特八肽基序上显示出有序的结构。
