Department of Life Sciences, Imperial College London, London, United Kingdom.
PLoS Biol. 2019 Aug 15;17(8):e3000405. doi: 10.1371/journal.pbio.3000405. eCollection 2019 Aug.
Case studies of the evolution of molecular machines remain scarce. One of the most diverse and widespread homologous families of machines is the type IV filament (TFF) superfamily, comprised of type IV pili, type II secretion systems (T2SSs), archaella, and other less-well-characterized families. These families have functions including twitching motility, effector export, rotary propulsion, nutrient uptake, DNA uptake, and even electrical conductance, but it is unclear how such diversity evolved from a common ancestor. In this issue, Denise and colleagues take a significant step toward understanding evolution of the TFF superfamily by determining a global phylogeny and using it to infer an evolutionary pathway. Results reveal that the superfamily predates the divergence of Bacteria and Archaea, and show how duplications, acquisitions, and losses coincide with changes in function. Surprises include that tight adherence (Tad) pili were horizontally acquired from Archaea and that T2SSs were relatively recently repurposed from type IV pili. Results also enable better understanding of the function of the ATPase family that powers the superfamily. The study highlights the role of tinkering by exaptation-the repurposing of pre-existing functions for new roles-in the diversification of molecular machines.
分子机器进化的案例研究仍然很少。最具多样性和广泛分布的机器同源家族之一是 IV 型丝（TFF）超家族，包括 IV 型菌毛、II 型分泌系统（T2SS）、古菌鞭毛和其他特征不太明显的家族。这些家族的功能包括蠕动运动、效应物输出、旋转推进、营养物质摄取、DNA 摄取，甚至电导，但尚不清楚这种多样性是如何从共同祖先进化而来的。在本期杂志中，Denise 及其同事通过确定全球系统发育并利用它推断进化途径，朝着理解 TFF 超家族的进化迈出了重要一步。研究结果表明，该超家族早于细菌和古菌的分化，并展示了重复、获取和损失如何与功能变化相一致。令人惊讶的是，紧密附着（Tad）菌毛是从古菌中水平获得的，而 T2SS 是最近才从 IV 型菌毛重新用于其他功能。研究结果还能更好地理解驱动该超家族的 ATP 酶家族的功能。该研究强调了通过适应性进化（即重新利用预先存在的功能来实现新的角色）在分子机器多样化中的作用。
