Milenkovic Vladimir M, Rivera Andrea, Horling Franziska, Weber Bernhard H F
Institute of Physiology, University of Regensburg, Franz-Josef-Strauss-Allee 11, D-93053 Regensburg, Germany.
J Biol Chem. 2007 Jan 12;282(2):1313-21. doi: 10.1074/jbc.M607383200. Epub 2006 Nov 15.
The vitelliform macular dystrophy type 2 (VMD2) gene mutated in Best macular dystrophy encodes a 585-amino acid putative transmembrane protein termed bestrophin-1. The vast majority of known disease-associated alterations are of the missense type, which cluster near predicted transmembrane domains (TMDs). To investigate bestrophin-1 membrane topology and to assess consequences of point mutations on membrane integration, we have analyzed the insertion of putative TMDs into the endoplasmic reticulum (ER) membrane. Out of six potential TMDs, our data suggest a topological model of bestrophin-1 with four transmembrane-spanning segments and one large cytoplasmatic loop between putative TMD2 and TMD5. Consequently, a relatively hydrophobic segment containing putative TMD3 (aa 130-149) and TMD4 (aa 179-201) is located within the cytoplasm. Furthermore, we show that three out of 18 disease-associated alterations investigated (I73N, Y85H, F281del) reveal measurable effects on membrane insertion suggesting that defective membrane integration of bestrophin-1 may represent a potential disease mechanism for a small subset of Best macular dystrophy-related mutations.
在贝斯特黄斑营养不良中发生突变的2型卵黄样黄斑营养不良（VMD2）基因编码一种含有585个氨基酸的假定跨膜蛋白，称为贝斯特罗芬1。绝大多数已知的与疾病相关的改变属于错义类型，它们聚集在预测的跨膜结构域（TMD）附近。为了研究贝斯特罗芬1的膜拓扑结构并评估点突变对膜整合的影响，我们分析了假定的TMD插入内质网（ER）膜的情况。在六个潜在的TMD中，我们的数据表明贝斯特罗芬1的拓扑模型有四个跨膜片段，在假定的TMD2和TMD5之间有一个大的细胞质环。因此，一个包含假定的TMD3（第130 - 149位氨基酸）和TMD4（第179 - 201位氨基酸）的相对疏水片段位于细胞质内。此外，我们发现，在所研究的18种与疾病相关的改变中，有三种（I73N、Y85H、F281del）对膜插入有可测量的影响，这表明贝斯特罗芬1的膜整合缺陷可能是一小部分与贝斯特黄斑营养不良相关突变的潜在疾病机制。
