Matsuzawa Fumiko, Aikawa Sei-ichi, Sakuraba Hitoshi, Lan Hoang Thi Ngoc, Tanaka Akemi, Ohno Kousaku, Sugimoto Yuko, Ninomiya Haruaki, Doi Hirofumi
Celestar Lexico-Sciences, Inc., MTG D-17, 1-3 Nakase, Mihama-ku, Chiba 261-8501, Japan.
J Hum Genet. 2003;48(11):582-9. doi: 10.1007/s10038-003-0082-7. Epub 2003 Oct 24.
To study the structural basis of the GM2 gangliosidosis B variant, we constructed the three-dimensional structures of the human beta-hexosaminidase alpha-subunit and the heterodimer of the alpha- and beta-subunits, Hex A, by homology modeling. The alpha-subunit is composed of two domains, domains I and II. Nine mutant models due to specific missense mutations were constructed as well and compared with the wild type to determine structural defects. These nine mutations were divided into five groups according to structural defects. R178H is deduced to affect the active site directly, because R178 is important for binding to the substrate. C458Y and W420C are predicted to cause drastic structural changes in the barrel structure carrying the active site pocket. R504C/H is deduced to introduce a disruption of an essential binding with D494 in the beta-subunit for dimerization. R499C/H, located in an extra-helix, is deduced to disrupt hydrogen bonds with domain I and the barrel. R170W and L484P are deduced to affect the interface between domains I and II, causing destabilization. The structural defects reflect the biochemical abnormalities of the disease.
为了研究GM2神经节苷脂贮积症B变异型的结构基础，我们通过同源建模构建了人β-己糖胺酶α亚基以及α亚基和β亚基的异二聚体Hex A的三维结构。α亚基由两个结构域，即结构域I和结构域II组成。还构建了由于特定错义突变导致的九个突变模型，并与野生型进行比较以确定结构缺陷。这九个突变根据结构缺陷分为五组。R178H被推断直接影响活性位点，因为R178对于与底物结合很重要。C458Y和W420C预计会在携带活性位点口袋的桶状结构中引起剧烈的结构变化。R504C/H被推断会导致与β亚基中用于二聚化的D494的关键结合中断。位于额外螺旋中的R499C/H被推断会破坏与结构域I和桶状结构的氢键。R170W和L484P被推断会影响结构域I和II之间的界面，导致不稳定。结构缺陷反映了该疾病的生化异常。
