Feng X, Lilly A A, Hazelbauer G L
Department of Biochemistry and Biophysics, Washington State University, Pullman, Washington 99164-4660, USA.
J Bacteriol. 1999 May;181(10):3164-71. doi: 10.1128/JB.181.10.3164-3171.1999.
In Escherichia coli, high-abundance chemoreceptors are present in cellular amounts approximately 10-fold higher than those of low-abundance receptors. These two classes exhibit inherent differences in functional activity. As sole cellular chemoreceptors, high-abundance receptors are effective in methyl-accepting activity, in establishing a functional balance between the two directions of flagellar rotation, in timely adaptation, and in mediating efficient chemotaxis. Low-abundance receptors are not, even when their cellular content is increased. We found that the low-abundance receptor Trg acquired essential functional features of a high-abundance receptor by the addition of the final 19 residues of the high-abundance receptor Tsr. The carboxy terminus of this addition carried a methyltransferase-binding pentapeptide, NWETF, present in high-abundance receptors but absent in the low-abundance class. Provision of this docking site not only enhanced steady-state and adaptational methylation but also shifted the abnormal, counterclockwise bias of flagellar rotation toward a more normal rotational balance and vastly improved chemotaxis in spatial gradients. These improvements can be understood as the result of both enhanced kinase activation by the more methylated receptor and timely adaptation by more efficient methyl-accepting activity. We conclude that the crucial functional difference between the low-abundance receptor Trg and its high-abundance counterparts is the level of methyl-accepting activity conferred by the methyltransferase-docking site.
在大肠杆菌中，高丰度化学感受器的细胞含量比低丰度感受器高出约10倍。这两类感受器在功能活性上存在内在差异。作为唯一的细胞化学感受器，高丰度感受器在甲基接受活性、在建立鞭毛旋转两个方向之间的功能平衡、在及时适应以及在介导高效趋化性方面均有效。即使增加其细胞含量，低丰度感受器也不具备这些功能。我们发现，通过添加高丰度感受器Tsr的最后19个残基，低丰度感受器Trg获得了高丰度感受器的基本功能特征。添加部分的羧基末端带有一个甲基转移酶结合五肽NWETF，该五肽存在于高丰度感受器中，而在低丰度感受器类别中不存在。提供这个对接位点不仅增强了稳态甲基化和适应性甲基化，还将鞭毛旋转异常的逆时针偏向转变为更正常的旋转平衡，并极大地改善了在空间梯度中的趋化性。这些改善可以理解为是由于甲基化程度更高的感受器增强了激酶激活以及更高效的甲基接受活性实现了及时适应的结果。我们得出结论，低丰度感受器Trg与其高丰度对应物之间关键的功能差异在于甲基转移酶对接位点赋予的甲基接受活性水平。
