The Voltage-Gated Na+ Channel Co-localizes with Methyl-Accepting Chemotaxis Proteins ofAlkaliphile at a Cell Pole

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The bacterial ion channels are useful for the structural analysis of the eukaryotic ion channels. The elucidation of physiologic functions and effecter proteins of the bacterial ion channels is important in research of the ion channels. NavBP is the member of the bacterial voltage-gated Na+ channel superfamily that is found in alkaliphilic Bacillus pseudofirmus OF4. NavBP has recently been shown to have a role in pH homeostasis, motility and chemotaxis. The chemotaxis phenotype of NavBP deletion mutant was particularly striking in that the response of the mutants to chemoattractants was inverted compared to the wild-type strain. Therefore, we have studied to elucidate the relation of the deficit of Na channel and the abnormalities in chemotaxis. We have already reported the following things. First, in the wild-type strain, colocalization of NavBP and the putative chemotaxis receptor McpX was observed at cell pole by immuno fluorescent microscopy (IFM). Second, in the NavBP deletion mutant, although the expression level of McpX did not change mostly, but the localization of that was decreased. Then, in order to observe cellullar localization of NavBP in a live cell, the plasmid which express the NavBP-CFP fusion protein was constructed, the transformation was carried out to NavBP deletion mutant. As a result, polar localization of functional NavBP-CFP was observed. The polar localization of NavBP in alkaliphilic Bacillus pseudofirmus OF4 was strongly suggested. In order for a chemotaxis receptor to function, it is necessary to localized at cell pole. The results suggest interactions between NavBP and McpX that affect their co-localization at cell pole. The inverse chemotaxis phenotype of NavBP deletion mutants may result in part from delocalization of McpX.