Discrimination between Different Methylation States of Chemotaxis Receptor Tar by Receptor Methyltransferase CheR
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- 作者：Eduardo Perez ; Ann H. West ; Ann M. Stock ; and Snezana Djordjevic
- 刊名：Biochemistry
- 出版年：2004
- 出版时间：February 3, 2004
- 年：2004
- 卷：43
- 期：4
- 页码：953 - 961
- 全文大小：285K
- 年卷期：v.43,no.4(February 3, 2004)
- ISSN：1520-4995
文摘
Bacterial chemotaxis receptors are posttranslationally modified by carboxyl methylation ofspecific glutamate residues within their cytoplasmic domains. This highly regulated, reversible modificationcounterbalances the signaling effects of ligand binding and contributes to adaptation. On the basis of thecrystal structure of the 
-glutamyl methyltransferase CheR, we have postulated that positively chargedresidues in helix 
2 in the N-terminal domain of the enzyme may be complementary to the negativelycharged methylation region of the methyltransferase substrates, the bacterial chemotaxis receptors. Severalaltered CheR proteins, in which positively charged arginine or lysine residues were substituted with alanines,were constructed and assayed for their methylation activities toward wild-type receptor and a series ofreceptor variants containing different glutamates available for methylation. One of the CheR mutant proteins(Arg53Ala) showed significantly lower activity toward all receptor constructs, suggesting that Arg53 mayplay a general role in catalysis of methyl transfer. The rest of the mutant proteins exhibited differentpatterns of relative methylation rates toward different receptor substrates, indicating specificity, probablythrough interaction of CheR with the receptor at sites distal to the specific site of methylation. The findingsimply complementarity between positively charged residues of the 2 helix of CheR and the negativelycharged glutamates of the receptor. It is likely that this complementarity is involved in discriminatingdifferent methylation states of the receptors.
-glutamyl methyltransferase CheR, we have postulated that positively chargedresidues in helix 2 in the N-terminal domain of the enzyme may be complementary to the negativelycharged methylation region of the methyltransferase substrates, the bacterial chemotaxis receptors. Severalaltered CheR proteins, in which positively charged arginine or lysine residues were substituted with alanines,were constructed and assayed for their methylation activities toward wild-type receptor and a series ofreceptor variants containing different glutamates available for methylation. One of the CheR mutant proteins(Arg53Ala) showed significantly lower activity toward all receptor constructs, suggesting that Arg53 mayplay a general role in catalysis of methyl transfer. The rest of the mutant proteins exhibited differentpatterns of relative methylation rates toward different receptor substrates, indicating specificity, probablythrough interaction of CheR with the receptor at sites distal to the specific site of methylation. The findingsimply complementarity between positively charged residues of the 2 helix of CheR and the negativelycharged glutamates of the receptor. It is likely that this complementarity is involved in discriminatingdifferent methylation states of the receptors.