Pilsl H, Braun V
Universität Tübingen, Germany.
Mol Microbiol. 1995 Apr;16(1):57-67. doi: 10.1111/j.1365-2958.1995.tb02391.x.
Uptake of a new colicin, colicin 10 (Col10), into cells of Escherichia coli required TonB, ExbBD (Ton system), but its cognate receptor, Tsx, functioned independently of Ton and TolQRAB (Tol system). Uptake of Col10 also required TolC which is unique for a Ton-coupled translocation through the outer membrane. A 2470 bp DNA fragment from the natural plasmid pCol10 encoding the Col10 activity (cta), immunity (cti) and lysis (ctl) genes was sequenced. The Cta, Cti and Ctl proteins, as deduced from the nucleotide sequences, consisted of 490 (M(r) 53,342), 96 (M(r) 11,586) and 43 (M(r) 4484) amino acid residues, respectively. Col10 (Cta) was highly homologous to colicin E1 in two regions which determined the common TolC requirement for uptake and the pore-forming activity. Col10 and E1 differed entirely in the regions which are predicted to determine the Ton dependence of Col10 and the Tol dependence of E1, and binding to the receptors Tsx and BtuB, respectively. The region responsible for the Ton-dependent uptake of Col10 was localized in the sequence ranging from residues 1 to 43 (Ton region), and the region responsible for the Tol-dependent uptake of colicin E1 extended from residues 1 to 34 (Tol region). Each Tol-dependent colicin contained a pentapeptide homologous to the sequence DGSGS in the Tol region of E1 which is proposed to be implicated in Tol-dependent uptake (TolA box). After the exchange of the Ton and the Tol regions between Col10 and E1, the Col10-E1 fusion protein was carried into cells via the Ton system and BtuB, whereas the E1-Col10 fusion protein was imported via the Tol system and Tsx. Although the immunity proteins of Col10 and E1 displayed a low homology, Cti conferred full immunity to E1, in contrast to the immunity protein of E1 which did not protect cells against Col10. It is proposed that Col10 belongs to the colicin E1, Ia, Ib group as opposed to the colicin A, B, N group of pore-forming colicins. Col10 consists of 4 domains of which two are very similar and two are very different to E1, supporting our previous proposal that colicins evolved by recombination of DNA fragments which encode uptake and activity domains.
一种新的大肠杆菌素——大肠杆菌素10（Col10）进入大肠杆菌细胞需要TonB、ExbBD（Ton系统），但其同源受体Tsx的功能独立于Ton和TolQRAB（Tol系统）。Col10的摄取还需要TolC，这对于通过外膜的Ton偶联转运来说是独特的。对来自天然质粒pCol10的一个2470 bp DNA片段进行了测序，该片段编码Col10活性（cta）、免疫（cti）和裂解（ctl）基因。从核苷酸序列推导的Cta、Cti和Ctl蛋白分别由490个（M(r) 53342）、96个（M(r) 11586）和43个（M(r) 4484）氨基酸残基组成。Col10（Cta）在两个区域与大肠杆菌素E1高度同源，这两个区域决定了摄取和形成孔道活性对TolC的共同需求。Col10和E1在预计分别决定Col10对Ton的依赖性和E1对Tol的依赖性以及与受体Tsx和BtuB结合的区域完全不同。负责Col10依赖Ton摄取的区域定位在从第1至43位残基的序列中（Ton区域），而负责大肠杆菌素E1依赖Tol摄取的区域从第1至34位残基延伸（Tol区域）。每种依赖Tol的大肠杆菌素在E1的Tol区域都含有一个与序列DGSGS同源的五肽，该序列被认为与依赖Tol的摄取有关（TolA框）。在Col10和E1之间交换Ton和Tol区域后，Col10-E1融合蛋白通过Ton系统和BtuB被带入细胞，而E1-Col10融合蛋白通过Tol系统和Tsx被导入。尽管Col10和E1的免疫蛋白显示出低同源性，但Cti赋予了对E1的完全免疫，这与E1的免疫蛋白不能保护细胞免受Col10侵害形成对比。有人提出Col10属于大肠杆菌素E1、Ia、Ib组，与形成孔道的大肠杆菌素A组、B组、N组相对。Col10由4个结构域组成，其中两个与E1非常相似，两个与E1非常不同，这支持了我们之前的提议，即大肠杆菌素是通过编码摄取和活性结构域的DNA片段重组进化而来的。
