Shu Chuanjun, Xiao Ke, Yan Qin, Sun Xiao
State Key Laboratory of Bioelectronics, School of Biological Science and Medical Engineering, Southeast University Nanjing, China.
Front Microbiol. 2016 Dec 21;7:2080. doi: 10.3389/fmicb.2016.02080. eCollection 2016.
During anaerobic respiration, the bacteria can transfer electrons to extracellular electron accepters through its pilus. pili have been reported to have metallic-like conductivity that is similar to doped organic semiconductors. To study the characteristics and origin of conductive pilin proteins found in the pilus structure, their genetic, structural, and phylogenetic properties were analyzed. The genetic relationships, and conserved structures and sequences that were obtained were used to predict the evolution of the pilins. Homologous genes that encode conductive pilin were found using PilFind and Cluster. Sequence characteristics and protein tertiary structures were analyzed with MAFFT and QUARK, respectively. The origin of conductive pilins was explored by building a phylogenetic tree. Truncation is a characteristic of conductive pilin. The structures of truncated pilins and their accompanying proteins were found to be similar to the N-terminal and C-terminal ends of full-length pilins respectively. The emergence of the truncated pilins can probably be ascribed to the evolutionary pressure of their extracellular electron transporting function. Genes encoding truncated pilins and proteins similar to the C-terminal of full-length pilins, which contain a group of consecutive anti-parallel beta-sheets, are adjacent in bacterial genomes. According to the genetic, structure, and phylogenetic analyses performed in this study, we inferred that the truncated pilins and their accompanying proteins probably evolved from full-length pilins by gene fission through duplication, degeneration, and separation. These findings provide new insights about the molecular mechanisms involved in long-range electron transport along the conductive pili of species.
在无氧呼吸过程中，细菌可通过菌毛将电子传递给细胞外电子受体。据报道，菌毛具有类似金属的导电性，类似于掺杂的有机半导体。为了研究菌毛结构中发现的导电菌毛蛋白的特性和起源，对其遗传、结构和系统发育特性进行了分析。利用获得的遗传关系、保守结构和序列来预测菌毛蛋白的进化。使用PilFind和Cluster查找编码导电菌毛蛋白的同源基因。分别用MAFFT和QUARK分析序列特征和蛋白质三级结构。通过构建系统发育树探索导电菌毛蛋白的起源。截短是导电菌毛蛋白的一个特征。发现截短的菌毛蛋白及其伴随蛋白的结构分别与全长菌毛蛋白的N末端和C末端相似。截短的菌毛蛋白的出现可能归因于其细胞外电子传输功能的进化压力。编码截短的菌毛蛋白和类似于全长菌毛蛋白C末端的蛋白质的基因，其中包含一组连续的反平行β折叠，在细菌基因组中相邻。根据本研究进行的遗传、结构和系统发育分析，我们推断截短的菌毛蛋白及其伴随蛋白可能是通过重复、退化和分离的基因裂变从全长菌毛蛋白进化而来的。这些发现为物种导电菌毛长距离电子传输所涉及的分子机制提供了新的见解。
