Shiga Kazuo, Yoshioka Hiroki, Matsumiya Teruhiko, Kimura Ichiro, Takeda Shin'ichi, Imamura Michihiro
Department of Molecular Therapy, National Institute of Neuroscience, NCNP, 4-1-1 Ogawahigashi-cho, Kodaira, Tokyo 187-8502, Japan.
Exp Cell Res. 2006 Jul 1;312(11):2083-92. doi: 10.1016/j.yexcr.2006.03.011. Epub 2006 Apr 25.
The sarcoglycans (SGs), transmembrane components of the dystrophin-associated glycoprotein complex, are stable and functional only when they assemble into a tetrameric complex in muscle cells. A defect in any one of the four SG members disrupts the entire SG complex (SGC) and causes limb-girdle muscular dystrophy. zeta-SG has been recently found as a transmembrane protein homologous to gamma-SG and delta-SG. To characterize zeta-SG in complex formation, we co-transfected expression vectors encoding all six SGs (alpha-, beta-, gamma-, delta-, epsilon- and zeta-SG) and dystroglycan into Chinese hamster ovary cells. Immunoprecipitation analysis showed that zeta-SG or gamma-SG formed a SGC with beta-SG and delta-SG plus alpha-SG or epsilon-SG, revealing that zeta-SG can form two types of SGCs (alpha-beta-zeta-delta or epsilon-beta-zeta-delta). This result indicates the functional resemblance of zeta-SG to gamma-SG rather than delta-SG, although phylogenetic analysis suggests that zeta-SG is evolutionally closer to delta-SG than to gamma-SG. Reverse transcription (RT)-PCR showed that the expression pattern of the transcript was almost the reciprocal of that of gamma-SG in various mouse tissues and that the zeta-SG transcript was especially abundant in the brain, suggesting that zeta-SG might play a particular role in the central nervous system.
肌聚糖（SGs）是肌营养不良蛋白相关糖蛋白复合体的跨膜成分，只有在肌肉细胞中组装成四聚体复合体时才稳定且具有功能。四种SG成员中任何一种出现缺陷都会破坏整个SG复合体（SGC），并导致肢带型肌营养不良。ζ-SG最近被发现是一种与γ-SG和δ-SG同源的跨膜蛋白。为了表征ζ-SG在复合体形成中的特性，我们将编码所有六种SG（α-、β-、γ-、δ-、ε-和ζ-SG）和肌聚糖的表达载体共转染到中国仓鼠卵巢细胞中。免疫沉淀分析表明，ζ-SG或γ-SG与β-SG和δ-SG加上α-SG或ε-SG形成了SGC，这表明ζ-SG可以形成两种类型的SGC（α-β-ζ-δ或ε-β-ζ-δ）。这一结果表明ζ-SG在功能上与γ-SG而非δ-SG相似，尽管系统发育分析表明ζ-SG在进化上与δ-SG比与γ-SG更接近。逆转录（RT）-PCR显示，该转录本的表达模式在各种小鼠组织中几乎与γ-SG的相反，并且ζ-SG转录本在脑中特别丰富，这表明ζ-SG可能在中枢神经系统中发挥特殊作用。
