National Centre for Biological Sciences, Tata Institute of Fundamental Research, Bangalore, India.
Biophys J. 2013 Jun 4;104(11):2553-63. doi: 10.1016/j.bpj.2013.03.066.
Extant eukaryotic cells have a dynamic traffic network that consists of diverse membrane-bound organelles exchanging matter via vesicles. This endomembrane system arose and diversified during a period characterized by massive expansions of gene families involved in trafficking after the acquisition of a mitochondrial endosymbiont by a prokaryotic host cell >1.8 billion years ago. Here we investigate the mechanistic link between gene duplication and the emergence of new nonendosymbiotic organelles, using a minimal biophysical model of traffic. Our model incorporates membrane-bound compartments, coat proteins and adaptors that drive vesicles to bud and segregate cargo from source compartments, and SNARE proteins and associated factors that cause vesicles to fuse into specific destination compartments. In simulations, arbitrary numbers of compartments with heterogeneous initial compositions segregate into a few compositionally distinct subsets that we term organelles. The global structure of the traffic system (i.e., the number, composition, and connectivity of organelles) is determined completely by local molecular interactions. On evolutionary timescales, duplication of the budding and fusion machinery followed by loss of cross-interactions leads to the emergence of new organelles, with increased molecular specificity being necessary to maintain larger organellar repertoires. These results clarify potential modes of early eukaryotic evolution as well as more recent eukaryotic diversification.
现存的真核细胞拥有一个动态的交通网络，由各种通过囊泡交换物质的膜结合细胞器组成。这个内膜系统是在大约 18 亿年前，一个原核宿主细胞获得一个线粒体内共生体之后，参与运输的基因家族发生大规模扩张和多样化的过程中出现和多样化的。在这里，我们使用交通的最小生物物理模型来研究基因复制和新的非内共生细胞器出现之间的机制联系。我们的模型包含膜结合区室、驱动囊泡出芽和将货物从源区室分离的衣壳蛋白和衔接蛋白，以及导致囊泡融合到特定目标区室的 SNARE 蛋白和相关因子。在模拟中，具有异质初始组成的任意数量的区室会分离成几个组成上明显不同的子集，我们称之为细胞器。交通系统的全局结构（即细胞器的数量、组成和连接性）完全由局部分子相互作用决定。在进化时间尺度上，出芽和融合机制的复制，随后失去交叉相互作用，导致新细胞器的出现，增加分子特异性对于维持更大的细胞器库是必要的。这些结果阐明了早期真核生物进化的潜在模式以及最近的真核生物多样化。
