Department of Biochemistry and Molecular Genetics, University of Virginia School of Medicine, Charlottesville, VA, USA.
Department of Chemistry, University of California, Irvine, Irvine, CA, USA.
Nat Microbiol. 2022 Aug;7(8):1291-1300. doi: 10.1038/s41564-022-01159-z. Epub 2022 Jul 7.
Electrically conductive appendages from the anaerobic bacterium Geobacter sulfurreducens were first observed two decades ago, with genetic and biochemical data suggesting that conductive fibres were type IV pili. Recently, an extracellular conductive filament of G. sulfurreducens was found to contain polymerized c-type cytochrome OmcS subunits, not pilin subunits. Here we report that G. sulfurreducens also produces a second, thinner appendage comprised of cytochrome OmcE subunits and solve its structure using cryo-electron microscopy at ~4.3 Å resolution. Although OmcE and OmcS subunits have no overall sequence or structural similarities, upon polymerization both form filaments that share a conserved haem packing arrangement in which haems are coordinated by histidines in adjacent subunits. Unlike OmcS filaments, OmcE filaments are highly glycosylated. In extracellular fractions from G. sulfurreducens, we detected type IV pili comprising PilA-N and -C chains, along with abundant B-DNA. OmcE is the second cytochrome filament to be characterized using structural and biophysical methods. We propose that there is a broad class of conductive bacterial appendages with conserved haem packing (rather than sequence homology) that enable long-distance electron transport to chemicals or other microbial cells.
二十年前，首次观察到厌氧细菌脱硫弧菌的导电附属物，遗传和生化数据表明导电纤维是 IV 型菌毛。最近，发现脱硫弧菌的细胞外导电丝含有聚合的 c 型细胞色素 OmcS 亚基，而不是菌毛亚基。在这里，我们报告说，脱硫弧菌还产生了第二种更细的附属物，由细胞色素 OmcE 亚基组成，并使用 ~4.3 Å 分辨率的冷冻电子显微镜解决了其结构。尽管 OmcE 和 OmcS 亚基没有总体序列或结构相似性，但在聚合后，两者都形成了具有保守血红素堆积排列的纤维，其中血红素由相邻亚基中的组氨酸配位。与 OmcS 纤维不同，OmcE 纤维高度糖基化。在从脱硫弧菌中检测到的细胞外部分中，我们检测到了包含 PilA-N 和 -C 链的 IV 型菌毛，以及丰富的 B-DNA。OmcE 是使用结构和生物物理方法表征的第二种细胞色素纤维。我们提出，存在一类具有保守血红素堆积（而不是序列同源性）的广泛导电细菌附属物，能够实现长距离电子向化学物质或其他微生物细胞的传输。
