Department of Chemistry, Britannia House, 7 Trinity Street, King's College London, London, UK.
Department of Physics, Freie Universität Berlin, Arnimallee 14, 14195, Dahlem, Germany.
Sci Rep. 2017 Aug 14;7(1):8021. doi: 10.1038/s41598-017-08522-9.
Correctly folded membrane proteins underlie a plethora of cellular processes, but little is known about how they fold. Knowledge of folding mechanisms centres on reversible folding of chemically denatured membrane proteins. However, this cannot replicate the unidirectional elongation of the protein chain during co-translational folding in the cell, where insertion is assisted by translocase apparatus. We show that a lipid membrane (devoid of translocase components) is sufficient for successful co-translational folding of two bacterial α-helical membrane proteins, DsbB and GlpG. Folding is spontaneous, thermodynamically driven, and the yield depends on lipid composition. Time-resolving structure formation during co-translational folding revealed different secondary and tertiary structure folding pathways for GlpG and DsbB that correlated with membrane interfacial and biological transmembrane amino acid hydrophobicity scales. Attempts to refold DsbB and GlpG from chemically denatured states into lipid membranes resulted in extensive aggregation. Co-translational insertion and folding is thus spontaneous and minimises aggregation whilst maximising correct folding.
正确折叠的膜蛋白是许多细胞过程的基础，但人们对它们如何折叠知之甚少。折叠机制的知识集中在化学变性膜蛋白的可逆折叠上。然而，这不能复制细胞中翻译共折叠过程中蛋白质链的单向延伸，在该过程中，易位酶装置协助插入。我们表明，脂质膜（不含易位酶成分）足以成功地进行两种细菌α-螺旋膜蛋白 DsbB 和 GlpG 的翻译共折叠。折叠是自发的，热力学驱动的，产率取决于脂质组成。在翻译共折叠过程中对结构形成进行时间分辨，揭示了 GlpG 和 DsbB 的不同二级和三级结构折叠途径，与膜界面和生物跨膜氨基酸疏水性尺度相关。从化学变性状态将 DsbB 和 GlpG 重新折叠到脂质膜中的尝试导致广泛的聚集。因此，翻译共插入和折叠是自发的，最大限度地减少聚集，同时最大限度地提高正确折叠的效率。
