Niwano M, Taylor B L
Proc Natl Acad Sci U S A. 1982 Jan;79(1):11-5. doi: 10.1073/pnas.79.1.11.
The involvement of methylation in the chemosensory response of bacteria to many attractants has been clearly established by studies in several laboratories. It has been assumed that adaptation of Salmonella typhimurium and Escherichia coli to all attractants involves methylation of a transmembrane methyl-accepting chemotaxis protein. The methyl donor in this reaction is S-adenosyl-L-methionine, and the protein methyltransferase is the product of the cheR gene. In contrast, adaptation to oxygen and phosphotransferase substrates were found to be independent of this methylation system. In E. coli AW660 (tsr tar trg), which lacks the known methyl-accepting chemotaxis proteins, chemotaxis was normal to oxygen and to substrates of the phosphotransferase system such as D-mannose, D-glucose, and N-acetyl-D-glucosamine. When S-adenosyl-L-methionine was depleted by methionine starvation or by addition of 1-aminocyclopentane-1-carboxylic acid, methylation-dependent adaptation to serine, aspartate, and ribose was defective in wild-type E. coli and S. typhimurium. However, adaptation to oxygen and phosphotransferase substrates was independent of S-adenosyl-L-methionine and the cheR product. These results suggest that there are methylation-independent and methylation-dependent mechanisms for sensory adaptation in bacteria.
多个实验室的研究已明确证实甲基化参与了细菌对多种引诱剂的化学感应反应。人们认为，鼠伤寒沙门氏菌和大肠杆菌对所有引诱剂的适应性都涉及一种跨膜甲基接受趋化蛋白的甲基化。此反应中的甲基供体是S-腺苷-L-甲硫氨酸，蛋白甲基转移酶是cheR基因的产物。相比之下，发现对氧气和磷酸转移酶底物的适应性与这种甲基化系统无关。在缺乏已知甲基接受趋化蛋白的大肠杆菌AW660（tsr tar trg）中，对氧气和磷酸转移酶系统的底物（如D-甘露糖、D-葡萄糖和N-乙酰-D-葡糖胺）的趋化作用正常。当通过甲硫氨酸饥饿或添加1-氨基环戊烷-1-羧酸使S-腺苷-L-甲硫氨酸耗尽时，野生型大肠杆菌和鼠伤寒沙门氏菌中对丝氨酸、天冬氨酸和核糖的甲基化依赖性适应性出现缺陷。然而，对氧气和磷酸转移酶底物的适应性与S-腺苷-L-甲硫氨酸和cheR产物无关。这些结果表明，细菌中存在与甲基化无关和与甲基化有关的感觉适应机制。
