Sandkvist M, Hirst T R, Bagdasarian M
Institute for Applied Cell and Molecular Biology, Umeå University, Sweden.
J Bacteriol. 1987 Oct;169(10):4570-6. doi: 10.1128/jb.169.10.4570-4576.1987.
The gene encoding the B subunit of heat-labile enterotoxin (etxB) was mutated at its 3' end by targeted addition of random nucleotide sequences. Gene products from five mutated etxB genes, all of which were shown to encode B subunits with short carboxy-terminal amino acid extensions, were analyzed with respect to a range of functional and structural properties. One class of altered B subunits, exemplified by EtxB124 and EtxB138, which both have seven extra amino acid residues, were found to be specifically defective in their ability to stably associate with A subunits and form holotoxin. Other altered B subunits were less subtlely affected by extensions at their C termini and were, in addition to their failure to associate with A subunits, unable to translocate into the periplasm of Escherichia coli, to pentamerize, or to bind to GM1 ganglioside. This suggests that the carboxy-terminal domain of EtxB mediates A subunit-B subunit interaction.
通过定向添加随机核苷酸序列，对编码不耐热肠毒素B亚基（etxB）的基因在其3'端进行了突变。分析了五个突变的etxB基因的基因产物，所有这些基因产物均显示编码具有短羧基末端氨基酸延伸的B亚基，并对一系列功能和结构特性进行了分析。一类改变的B亚基，以EtxB124和EtxB138为例，它们都有七个额外的氨基酸残基，被发现其与A亚基稳定结合并形成全毒素的能力存在特异性缺陷。其他改变的B亚基受其C末端延伸的影响较小，除了无法与A亚基结合外，还无法转运到大肠杆菌的周质中、形成五聚体或与GM1神经节苷脂结合。这表明EtxB的羧基末端结构域介导A亚基与B亚基的相互作用。
