Raychowdhury Malay K, González-Perrett Silvia, Montalbetti Nicolás, Timpanaro Gustavo A, Chasan Bernard, Goldmann Wolfgang H, Stahl Stefanie, Cooney Adele, Goldin Ehud, Cantiello Horacio F
Renal Unit, Massachusetts General Hospital East, Charlestown 02129, USA.
Hum Mol Genet. 2004 Mar 15;13(6):617-27. doi: 10.1093/hmg/ddh067. Epub 2004 Jan 28.
Mucolipidosis type IV (MLIV) is an autosomal recessive neurogenetic disorder characterized by developmental abnormalities of the brain and impaired neurological, ophthalmologic and gastric function. Large vacuoles accumulate in various types of cells in MLIV patients. However, the pathophysiology of the disease at the cellular level is still unknown. MLIV is caused by mutations in a recently described gene, MCOLN1, encoding mucolipin-1 (ML1), a 65 kDa protein whose function is also unknown. ML1 shows sequence homology and topological similarities with polycystin-2 and other transient receptor potential (Trp) channels. In this study, we assessed both, whether ML1 has ion channel properties, and whether disease-causing mutations in MCOLN1 have functional differences with the wild-type (WT) protein. ML1 channel function was assessed from endosomal vesicles of null (MCOLN1(-/-)) and ML1 over-expressing cells, and liposomes containing the in vitro translated protein. Evidence from both preparations indicated that WT ML1 is a multiple subconductance non-selective cation channel whose function is inhibited by a reduction of pH. The V446L and DeltaF408 MLIV causing mutations retain channel function but not the sharp inhibition by lowering pH. Atomic force imaging of ML1 channels indicated that changes in pH modified the aggregation of unitary channels. Mutant-ML1 did not change in size on reduction of pH. The data indicate that ML1 channel activity is regulated by a pH-dependent mechanism that is deficient in some MLIV causing mutations of the gene. The evidence also supports a novel role for cation channels in the acidification and normal endosomal function.
IV型粘脂贮积症（MLIV）是一种常染色体隐性神经遗传病，其特征为大脑发育异常以及神经、眼科和胃功能受损。MLIV患者的各类细胞中会积累大量液泡。然而，该疾病在细胞水平的病理生理学仍不清楚。MLIV是由最近发现的MCOLN1基因突变所致，该基因编码粘脂蛋白-1（ML1），这是一种65 kDa的蛋白质，其功能也尚不明确。ML1与多囊蛋白-2及其他瞬时受体电位（Trp）通道在序列上具有同源性，在拓扑结构上具有相似性。在本研究中，我们评估了ML1是否具有离子通道特性，以及MCOLN1中的致病突变与野生型（WT）蛋白在功能上是否存在差异。通过对缺失（MCOLN1(-/-)）和ML1过表达细胞的内体囊泡以及含有体外翻译蛋白的脂质体进行检测，评估ML1通道功能。两种制剂的证据均表明，WT ML1是一种多亚电导非选择性阳离子通道，其功能会因pH值降低而受到抑制。导致MLIV的V446L和DeltaF408突变保留了通道功能，但不会因pH值降低而受到明显抑制。ML1通道的原子力成像表明，pH值的变化改变了单通道的聚集情况。pH值降低时，突变型-ML1的大小没有变化。数据表明，ML1通道活性受pH值依赖机制调控，而该机制在一些导致MLIV的基因突变中存在缺陷。这些证据还支持阳离子通道在酸化和正常内体功能中具有新作用。
