Genetic, genomic, and functional analysis of the granule lattice proteins in Tetrahymena secretory granules
Genetic, genomic, and functional analysis of the granule lattice proteins in Tetrahymena secretory granules
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DOI：
10.1091/mbc.e05-01-0028
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发表时间：
2005-09-01
影响因子：
3.3
通讯作者：
Turkewitz, AP
中科院分区：
文献类型：
--
作者：
Cowan, AT;Bowman, GR;Turkewitz, AP
在一些细胞中，储存在致密的核心分泌颗粒中的多肽凝聚成有序的阵列。在纤毛虫中，如嗜热四膜虫，产生的晶体起到抛射物的作用，在胞吐时膨胀。颗粒内容物的分离以前定义了五种颗粒晶格(GRL)蛋白质作为丰富的核心成分，而功能筛选确定了第六个家族成员。我们现在已经扩展了这个屏幕，以确定弹丸组装所需的非冗余部件。结果进一步得到了基因破坏实验的支持，表明六种GRL蛋白定义了核心结构。体内和体外数据都表明，核心组装开始于内质网，形成特定的异源寡聚体GRL前蛋白复合体。在嗜热锥虫基因组中还发现了另外四个类似GRL的基因。Grl2p和Grl6p针对颗粒，但转录本存在于低水平，并且都不是核心组装所必需的。尽管如此，Delta GRL6细胞的颗粒形态发生了细微的变化，颗粒堆积明显减少。上位性分析表明，这是Delta GRL6颗粒加速丢失的结果，而不是合成减少的结果。我们的结果不仅为基于GRL的颗粒核心的组织提供了洞察力，也暗示了GRL蛋白的功能超出了核心组装的范围。
in some cells, the polypeptides stored in dense core secretory granules condense as ordered arrays. In ciliates such as Tetrahymena thermophila, the resulting crystals function as projectiles, expanding upon exocytosis. Isolation of granule contents previously defined five Granule lattice (Grl) proteins as abundant core constituents, whereas a functional screen identified a sixth family member. We have now expanded this screen to identify the nonredundant components required for projectile assembly. The results, further supported by gene disruption experiments, indicate that six Grl proteins define the core structure. Both in vivo and in vitro data indicate that core assembly begins in the endoplasmic reticulum with formation of specific hetero-oligomeric Grl proprotein complexes. Four additional GRL-like genes were found in the T. thermophila genome. Grl2p and Grl6p are targeted to granules, but the transcripts are present at low levels and neither is essential for core assembly. The Delta GRL6 cells nonetheless showed a subtle change in granule morphology and a marked reduction in granule accumulation. Epistasis analysis suggests this results from accelerated loss of Delta GRL6 granules, rather than from decreased synthesis. Our results not only provide insight into the organization of Grl-based granule cores but also imply that the functions of Grl proteins extend beyond core assembly.