Weissenbach Julia, Ilhan Judith, Bogumil David, Hülter Nils, Stucken Karina, Dagan Tal
Institute of General Microbiology, Christian-Albrechts University of Kiel, Am Botanischen Garten 11, Kiel, Germany.
Genome Biol Evol. 2017 Jan 1;9(1):241-252. doi: 10.1093/gbe/evw287.
Chaperonins promote protein folding and are known to play a role in the maintenance of cellular stability under stress conditions. The group I bacterial chaperonin complex comprises GroEL, that forms a barrel-like oligomer, and GroES that forms the lid. In most eubacteria the GroES/GroEL chaperonin is encoded by a single-copy bicistronic operon, whereas in cyanobacteria up to three groES/groEL paralogs have been documented. Here we study the evolution and functional diversification of chaperonin paralogs in the heterocystous, multi-seriate filament forming cyanobacterium Chlorogloeopsis fritschii PCC 6912. The genome of C. fritschii encodes two groES/groEL operons (groESL1, groESL1.2) and a monocistronic groEL gene (groEL2). A phylogenetic reconstruction reveals that the groEL2 duplication is as ancient as cyanobacteria, whereas the groESL1.2 duplication occurred at the ancestor of heterocystous cyanobacteria. A comparison of the groEL paralogs transcription levels under different growth conditions shows that they have adapted distinct transcriptional regulation. Our results reveal that groEL1 and groEL1.2 are upregulated during diazotrophic conditions and the localization of their promoter activity points towards a role in heterocyst differentiation. Furthermore, protein-protein interaction assays suggest that paralogs encoded in the two operons assemble into hybrid complexes. The monocistronic encoded GroEL2 is not forming oligomers nor does it interact with the co-chaperonins. Interaction between GroES1.2 and GroEL1.2 could not be documented, suggesting that the groESL1.2 operon does not encode a functional chaperonin complex. Functional complementation experiments in Escherichia coli show that only GroES1/GroEL1 and GroES1/GroEL1.2 can substitute the native operon. In summary, the evolutionary consequences of chaperonin duplication in cyanobacteria include the retention of groESL1 as a housekeeping gene, subfunctionalization of groESL1.2 and neofunctionalization of the monocistronic groEL2 paralog.
伴侣蛋白促进蛋白质折叠，并且已知在应激条件下维持细胞稳定性方面发挥作用。第一类细菌伴侣蛋白复合体由形成桶状寡聚体的GroEL和形成盖子的GroES组成。在大多数真细菌中，GroES/GroEL伴侣蛋白由单拷贝双顺反子操纵子编码，而在蓝细菌中，已记录到多达三个groES/groEL旁系同源物。在这里，我们研究了异形、多列丝状蓝细菌弗里氏绿球藻PCC 6912中伴侣蛋白旁系同源物的进化和功能多样化。弗里氏绿球藻的基因组编码两个groES/groEL操纵子（groESL1、groESL1.2）和一个单顺反子groEL基因（groEL2）。系统发育重建表明，groEL2的复制与蓝细菌一样古老，而groESL1.2的复制发生在异形蓝细菌的祖先时期。对不同生长条件下groEL旁系同源物转录水平的比较表明，它们具有不同的转录调控。我们的结果表明，groEL1和groEL1.2在固氮条件下上调，其启动子活性的定位表明它们在异形胞分化中起作用。此外，蛋白质-蛋白质相互作用分析表明，两个操纵子中编码的旁系同源物组装成杂合复合体。单顺反子编码的GroEL2不形成寡聚体，也不与共伴侣蛋白相互作用。无法证明GroES1.2和GroEL1.2之间存在相互作用，这表明groESL1.2操纵子不编码功能性伴侣蛋白复合体。在大肠杆菌中的功能互补实验表明，只有GroES1/GroEL1和GroES1/GroEL1.2可以替代天然操纵子。总之，蓝细菌中伴侣蛋白复制的进化后果包括将groESL1保留为管家基因，groESL1.2的亚功能化和单顺反子groEL2旁系同源物的新功能化。
