The Receptor Binding Site for the Methyltransferase of Bacterial Chemotaxis Is Distinct from the Sites of Methylation
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- 作者：Jiongru Wu ; Jiayin Li ; Guoyong Li ; David G. Long ; and Robert M. Weis
- 刊名：Biochemistry
- 出版年：1996
- 出版时间：April 16, 1996
- 年：1996
- 卷：35
- 期：15
- 页码：4984 - 4993
- 全文大小：543K
- 年卷期：v.35,no.15(April 16, 1996)
- ISSN：1520-4995
文摘
The principal locus for binding interactions between the aspartateand serine receptors ofEscherichia coli and the methyltransferase was found to bein the last five amino acids of the receptor.The thermodynamic parameters of transferase-receptorinteractions were determined by isothermal titrationcalorimetry. The serine receptor and three C-terminal fragments(C-fragments) of the aspartate receptorconsisting of either the last 297, 88, or 38 amino acids gavecomparable values for binding (n = 1,
H
13 kcal/mol, and Ka 4 ×105 M-1). Truncating either 16 or 36amino acids from the C-terminuseliminated observable interactions. Finally the pentapeptideAsn-Trp-Glu-Thr-Phe, which correspondsto the last five amino acids of the receptor and is strictly conservedamong the E. coli serine andaspartatereceptors and the Salmonella typhimurium aspartate receptor,was found to have all the binding activityof the full-length receptor and the C-fragments. An invitro methylation assay was used to obtain evidencefor the physiological significance of this interaction in which excesspeptide was able to completely blockreceptor methylation. The location of the binding site far fromthe methylation sites in the primary structureof the receptor suggests that the principle role of this interactionmay be to hold the transferase in closeproximity to all of the methylation sites. Intersubunitmethylation is proposed as plausible consequenceof this "controlled proximity" mechanism since the ribose-galactoseand dipeptide receptors lack thetransferase binding sequence, and appear unable to bind transferase.Intersubunit methylation impliesthat transferase bound to either the serine or aspartate receptorsubunit may catalyze methylation of receptorsubunits in a neighboring dimer, including those that have differentligand specificity.
H 13 kcal/mol, and Ka 4 ×105 M-1). Truncating either 16 or 36amino acids from the C-terminuseliminated observable interactions. Finally the pentapeptideAsn-Trp-Glu-Thr-Phe, which correspondsto the last five amino acids of the receptor and is strictly conservedamong the E. coli serine andaspartatereceptors and the Salmonella typhimurium aspartate receptor,was found to have all the binding activityof the full-length receptor and the C-fragments. An invitro methylation assay was used to obtain evidencefor the physiological significance of this interaction in which excesspeptide was able to completely blockreceptor methylation. The location of the binding site far fromthe methylation sites in the primary structureof the receptor suggests that the principle role of this interactionmay be to hold the transferase in closeproximity to all of the methylation sites. Intersubunitmethylation is proposed as plausible consequenceof this "controlled proximity" mechanism since the ribose-galactoseand dipeptide receptors lack thetransferase binding sequence, and appear unable to bind transferase.Intersubunit methylation impliesthat transferase bound to either the serine or aspartate receptorsubunit may catalyze methylation of receptorsubunits in a neighboring dimer, including those that have differentligand specificity.