Ohno K, Engel A G, Brengman J M, Shen X M, Heidenreich F, Vincent A, Milone M, Tan E, Demirci M, Walsh P, Nakano S, Akiguchi I
Department of Neurology, Mayo Clinic, Rochester, MN 55905, USA.
Ann Neurol. 2000 Feb;47(2):162-70.
The end-plate species of acetylcholinesterase (AChE) is an asymmetric enzyme consisting of a collagenic tail subunit composed of three collagenic strands (ColQ), each attached to a tetramer of the T isoform of the catalytic subunit (AChE(T)) via a proline-rich attachment domain. The principal function of the tail subunit is to anchor asymmetric AChE in the synaptic basal lamina. Human end-plate AChE deficiency was recently shown to be caused by mutations in COLQ. We here report nine novel COLQ mutations in 7 patients with end-plate AChE deficiency. We examine the effects of the mutations on the assembly of asymmetric AChE by coexpressing each genetically engineered COLQ mutant with ACHE(T) in COS cells. We classify the newly recognized and previously reported COLQ mutations into four classes according to their position in ColQ and their effect on AChE expression. We find that missense mutations in the proline-rich attachment domain abrogate attachment of catalytic subunits, that truncation mutations in the ColQ collagen domain prevent the assembly of asymmetric AChE, that hydrophobic missense residues in the C-terminal domain prevent triple helical assembly of the ColQ collagen domain, and that other mutations in the C-terminal region produce asymmetric species of AChE that are likely insertion incompetent.
乙酰胆碱酯酶（AChE）的终板型是一种不对称酶，由一个胶原尾部亚基组成，该亚基由三条胶原链（ColQ）构成，每条链通过富含脯氨酸的连接结构域与催化亚基（AChE(T)）的T同工型四聚体相连。尾部亚基的主要功能是将不对称AChE锚定在突触基底膜中。最近发现人类终板AChE缺乏症是由COLQ突变引起的。我们在此报告了7例终板AChE缺乏症患者中的9种新的COLQ突变。我们通过在COS细胞中共表达每个基因工程化的COLQ突变体与ACHE(T)，来研究这些突变对不对称AChE组装的影响。我们根据新识别的和先前报道的COLQ突变在ColQ中的位置及其对AChE表达的影响，将它们分为四类。我们发现富含脯氨酸的连接结构域中的错义突变消除了催化亚基的连接，ColQ胶原结构域中的截短突变阻止了不对称AChE的组装，C末端结构域中的疏水性错义残基阻止了ColQ胶原结构域的三螺旋组装，并且C末端区域中的其他突变产生了可能无法插入的不对称AChE种类。
