Finnigan Gregory C, Takagi Julie, Cho Christina, Thorner Jeremy
Division of Biochemistry, Biophysics and Structural Biology, Department of Molecular and Cell Biology, University of California, Berkeley, California 94720-3202.
Department of Microbiology and Immunology, University of California School of Medicine, San Francisco, California 94158-2200.
Genetics. 2015 Jul;200(3):821-41. doi: 10.1534/genetics.115.176495. Epub 2015 May 12.
Septins are a family of GTP-binding proteins considered to be cytoskeletal elements because they self-assemble into filaments and other higher-order structures in vivo. In budding yeast, septins establish a diffusion barrier at the bud neck between a mother and daughter cell, promote membrane curvature there, and serve as a scaffold to recruit other proteins to the site of cytokinesis. However, the mechanism by which any septin engages a partner protein has been unclear. The two most related and recently evolved subunits appear to be Cdc11 and Shs1, and the basic building blocks for assembling septin structures are hetero-octameric rods (Cdc11-Cdc12-Cdc3-Cdc10-Cdc10-Cdc3-Cdc12-Cdc11 and Shs1-Cdc12-Cdc3-Cdc10-Cdc10-Cdc3-Cdc12-Shs1). Loss of Cdc11 is not normally tolerated, whereas cells lacking Shs1 do not appear grossly abnormal. We established several different sensitized genetic backgrounds wherein Shs1 is indispensable, which allowed us to carry out the first comprehensive and detailed genetic analysis of Shs1 in vivo. Our analysis revealed several novel insights, including: (i) the sole portion of Shs1 essential for its function is a predicted coiled-coil-forming segment in its C-terminal extension (CTE); (ii) the CTE of Cdc11 shares this function; (iii) this role for the CTEs of Cdc11 and Shs1 is quite distinct from that of the CTEs of Cdc3 and Cdc12; and (iv) heterotypic Cdc11 and Shs1 junctions likely occur in vivo.
Septins是一类GTP结合蛋白家族，因其在体内能自我组装成细丝和其他高阶结构，故而被视为细胞骨架成分。在芽殖酵母中，Septins在母细胞与子细胞之间的芽颈处建立扩散屏障，促进此处的膜曲率形成，并作为一种支架招募其他蛋白质至胞质分裂位点。然而，任何一种Septins与伴侣蛋白结合的机制尚不清楚。两个最相关且最近进化的亚基似乎是Cdc11和Shs1，组装Septins结构的基本构建单元是异源八聚体杆（Cdc11-Cdc12-Cdc3-Cdc10-Cdc10-Cdc3-Cdc12-Cdc11和Shs1-Cdc12-Cdc3-Cdc10-Cdc10-Cdc3-Cdc12-Shs1）。通常情况下，缺失Cdc11是无法耐受的，而缺乏Shs1的细胞看起来并无明显异常。我们建立了几种不同的敏感遗传背景，其中Shs1是不可或缺的，这使我们能够在体内对Shs1进行首次全面而详细的遗传分析。我们的分析揭示了几个新的见解，包括：（i）Shs1功能所必需的唯一部分是其C端延伸（CTE）中一个预测的卷曲螺旋形成段；（ii）Cdc11的CTE也具有此功能；（iii）Cdc11和Shs1的CTE的这一作用与Cdc3和Cdc12的CTE的作用截然不同；（iv）异型Cdc11和Shs1连接可能在体内发生。
