C termini of the Escherichia coli mechanosensitive ion channel (MscS) move apart upon the channel opening

Heptameric YggB is a mechanosensitive ion channel (MscS) from the inner membrane of Escherichia coli. We demonstrate, using the patch clamp technique, that cross-linking of the YggB C termini led to irreversible inhibition of the channel activities. Application of Ni2+ to the YggB-His, channels with the hexahistidine tags added to the ends of their C termini also resulted in a marked but reversible decrease of activities. Western blot revealed that YggB-His, oligomers are more stable in the presence of Ni2+, providing evidence that Ni2+ is coordinated between C termini from different subunits of the channel. Intersubunit coordination of Ni2+ affecting channel activities occurred in the channel closed conformation and not in the open state. This may suggest that the C termini move apart upon channel opening and are involved in the channel activation. We propose that the as yet undefined C-terminal region may form a cytoplasmic gate of the channel. The results are discussed and interpreted based on the recently released quaternary structure of the channel.