Molecular Biophysics Laboratory, Department of Biological Sciences, Indian Institute of Science Education and Research, Bhopal 462066, India.
Biochim Biophys Acta Biomembr. 2017 Dec;1859(12):2467-2482. doi: 10.1016/j.bbamem.2017.09.020. Epub 2017 Sep 22.
The biogenesis of transmembrane β-barrels (outer membrane proteins, or OMPs) is an elaborate multistep orchestration of the nascent polypeptide with translocases, barrel assembly machinery, and helper chaperone proteins. Several theories exist that describe the mechanism of chaperone-assisted OMP assembly in vivo and unassisted (spontaneous) folding in vitro. Structurally, OMPs of bacterial origin possess even-numbered strands, while mitochondrial β-barrels are even- and odd-stranded. Several underlying similarities between prokaryotic and eukaryotic β-barrels and their folding machinery are known; yet, the link in their evolutionary origin is unclear. While OMPs exhibit diversity in sequence and function, they share similar biophysical attributes and structure. Similarly, it is important to understand the intricate OMP assembly mechanism, particularly in eukaryotic β-barrels that have evolved to perform more complex functions. Here, we deliberate known facets of β-barrel evolution, folding, and stability, and attempt to highlight outstanding questions in β-barrel biogenesis and proteostasis.
跨膜β-桶（外膜蛋白或 OMP）的生物发生是新生多肽与移位酶、桶组装机制和辅助伴侣蛋白的精心编排的多步过程。有几种理论描述了体内伴侣蛋白辅助 OMP 组装和体外无辅助（自发）折叠的机制。结构上，源自细菌的 OMP 具有偶数个链，而线粒体β-桶具有偶数和奇数个链。已知真核生物和原核生物β-桶及其折叠机制之间存在一些潜在的相似性；然而，它们在进化起源上的联系尚不清楚。虽然 OMP 在序列和功能上表现出多样性，但它们具有相似的生物物理属性和结构。同样，了解复杂的 OMP 组装机制也很重要，特别是在进化为执行更复杂功能的真核β-桶中。在这里，我们详细讨论了β-桶进化、折叠和稳定性的已知方面，并试图强调β-桶生物发生和蛋白质稳定性方面的突出问题。
