Functional requirements for fukutin-related protein in the Golgi apparatus
Functional requirements for fukutin-related protein in the Golgi apparatus
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DOI：
10.1093/hmg/11.26.3319
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发表时间：
2002-12-15
影响因子：
3.5
通讯作者：
Blake, DJ
中科院分区：
文献类型：
--
作者：
Esapa, CT;Benson, MA;Blake, DJ
两种形式的先天性肌营养不良症(CMD)，福山CMD和CMD类型1C(MDC1C)是由编码两种假定的糖基转移酶--Fukutin和Fukutin相关蛋白(FKRP)的基因突变引起的。此外，FKRP基因的突变也会导致肢带型2I型肌营养不良症(LGMD2I)，这是一种比MDC1C温和得多的等位基因变异。所有这些疾病都与肌肉α-肌营养不良蛋白聚糖表达的继发性变化有关。为了阐明FKRP和Fukutin的功能并检查MDC1C患者突变的影响，我们确定了每种蛋白的亚细胞定位机制。FKRP和Fukutin通过其N-末端和跨膜结构域靶向内侧高尔基体。FKRP在CHO细胞中的过表达改变了α-和β-肌营养不良蛋白聚糖抑制两种异构体成熟的翻译后处理。蛋白质假定活性部位的DxD基序或高尔基体靶向序列中的突变，导致FKRP低效地输送到高尔基体，并没有改变营养不良糖蛋白在体外的加工过程。导致先天性肌营养不良的FKRP中的P448L突变改变了一种保守的氨基酸，导致突变蛋白在细胞中的错误定位，从而无法改变营养不良的处理。我们的数据表明，FKRP和Fukutin是高尔基体驻留的蛋白质，而FKRP是营养不良多糖翻译后修饰所必需的。一个错位的FKRP突变体引起的营养不良糖链的异常加工可能是导致先天性肌营养不良症的一种新机制。
Two forms of congenital muscular dystrophy (CMD), Fukuyama CMD and CMD type 1C (MDC1C) are caused by mutations in the genes encoding two putative glycosyltransferases, fukutin and fukutin-related protein (FKRP). Additionally, mutations in the FKRP gene also cause limb-girdle muscular dystrophy type 2I (LGMD2I), a considerably milder allelic variant than MDC1C. All of these diseases are associated with secondary changes in muscle alpha-dystroglycan expression. To elucidate the function of FKRP and fukutin and examine the effects of MDC1C patient mutations, we have determined the mechanism for the subcellular location of each protein. FKRP and fukutin are targeted to the medial-Golgi apparatus through their N-termini and transmembrane domains. Overexpression of FKRP in CHO cells alters the post-translational processing of alpha- and beta-dystroglycan inhibiting maturation of the two isoforms. Mutations in the DxD motif in the putative active site of the protein or in the Golgi-targeting sequence, which cause FKRP to be inefficiently trafficked to the Golgi apparatus, did not alter dystroglycan processing in vitro. The P448L mutation in FKRP that causes congenital muscular dystrophy changes a conserved amino acid resulting in the mislocalization of the mutant protein in the cell that is unable to alter dystroglycan processing. Our data show that FKRP and fukutin are Golgi-resident proteins and that FKRP is required for the post-translational modi cation of dystroglycan. Aberrant processing of dystroglycan caused by a mislocalized FKRP mutant could be a novel mechanism that causes congenital muscular dystrophy.