Akasaka-Manya Keiko, Manya Hiroshi, Nakajima Ai, Kawakita Masao, Endo Tamao
Glycobiology Research Group, Tokyo Metropolitan Institute of Gerontology, Foundation for Research on Aging and Promotion of Human Welfare, Tokyo 173-0015, Japan.
J Biol Chem. 2006 Jul 14;281(28):19339-45. doi: 10.1074/jbc.M601091200. Epub 2006 May 12.
A defect of protein O-mannosylation causes congenital muscular dystrophy with brain malformation and structural eye abnormalities, so-called Walker-Warburg syndrome. Protein O-mannosylation is catalyzed by protein O-mannosyltransferase 1 (POMT1) and its homologue, POMT2. Coexpression of POMT1 and POMT2 is required to show O-mannosylation activity. Here we have shown that POMT1 forms a complex with POMT2 and the complex possesses protein O-mannosyltransferase activity. Results indicate that POMT1 and POMT2 associate physically and functionally in vivo. Recently, three mutations were reported in the POMT1 gene of patients who showed milder phenotypes than typical Walker-Warburg syndrome. We coexpressed these mutant POMT1s with POMT2 and found that none of them had any activity. However, all POMT1 mutants, including previously identified POMT1 mutants, coprecipitated with POMT2. These results indicate that the mutant POMT1s could form heterocomplexes with POMT2 but that such complexes are insufficient for enzymatic activity.
蛋白质O-甘露糖基化缺陷会导致伴有脑畸形和眼部结构异常的先天性肌营养不良，即所谓的沃克-沃尔堡综合征。蛋白质O-甘露糖基化由蛋白质O-甘露糖基转移酶1（POMT1）及其同源物POMT2催化。POMT1和POMT2的共表达是显示O-甘露糖基化活性所必需的。在此我们表明，POMT1与POMT2形成复合物，且该复合物具有蛋白质O-甘露糖基转移酶活性。结果表明，POMT1和POMT2在体内存在物理和功能上的关联。最近，在表现出比典型沃克-沃尔堡综合征更轻表型的患者的POMT1基因中报道了三个突变。我们将这些突变型POMT1与POMT2共表达，发现它们均无任何活性。然而，所有POMT1突变体，包括先前鉴定出的POMT1突变体，都能与POMT2共沉淀。这些结果表明，突变型POMT1可以与POMT2形成异源复合物，但这种复合物不足以产生酶活性。
