Department of Biochemistry and Molecular Biology, Monash University, Clayton, Australia.
PLoS One. 2012;7(8):e43245. doi: 10.1371/journal.pone.0043245. Epub 2012 Aug 14.
Autotransporters are secreted proteins that are assembled into the outer membrane of bacterial cells. The passenger domains of autotransporters are crucial for bacterial pathogenesis, with some remaining attached to the bacterial surface while others are released by proteolysis. An enigma remains as to whether autotransporters should be considered a class of secretion system, or simply a class of substrate with peculiar requirements for their secretion. We sought to establish a sensitive search protocol that could identify and characterize diverse autotransporters from bacterial genome sequence data. The new sequence analysis pipeline identified more than 1500 autotransporter sequences from diverse bacteria, including numerous species of Chlamydiales and Fusobacteria as well as all classes of Proteobacteria. Interrogation of the proteins revealed that there are numerous classes of passenger domains beyond the known proteases, adhesins and esterases. In addition the barrel-domain-a characteristic feature of autotransporters-was found to be composed from seven conserved sequence segments that can be arranged in multiple ways in the tertiary structure of the assembled autotransporter. One of these conserved motifs overlays the targeting information required for autotransporters to reach the outer membrane. Another conserved and diagnostic motif maps to the linker region between the passenger domain and barrel-domain, indicating it as an important feature in the assembly of autotransporters.
自动转运蛋白是一种分泌蛋白，它们被组装到细菌细胞的外膜中。自动转运蛋白的载体结构域对细菌的发病机制至关重要，其中一些仍然附着在细菌表面，而另一些则通过蛋白水解释放。一个谜仍然存在，即自动转运蛋白是否应该被视为一类分泌系统，或者仅仅是一类具有特殊分泌要求的底物。我们试图建立一种敏感的搜索协议，可以从细菌基因组序列数据中识别和表征不同的自动转运蛋白。新的序列分析管道从各种细菌中鉴定出了超过 1500 种自动转运蛋白序列，包括衣原体和梭杆菌门的许多种以及所有类别的变形菌门。对这些蛋白质的分析表明，除了已知的蛋白酶、黏附素和酯酶之外，还有许多种不同的载体结构域。此外，桶状结构域——自动转运蛋白的一个特征——被发现由七个保守的序列片段组成，这些片段在组装好的自动转运蛋白的三级结构中可以以多种方式排列。其中一个保守基序覆盖了自动转运蛋白到达外膜所需的靶向信息。另一个保守且具有诊断意义的基序映射到载体结构域和桶状结构域之间的连接区，表明它是自动转运蛋白组装中的一个重要特征。
