ProP-ProP and ProP-phospholipid interactions determine the subcellular distribution of osmosensing transporter ProP...

Osmosensing transporter ProP protects bacteria from osmotically induced dehydration by mediating the uptake of zwitterionic osmolytes. ProP activity is a sigmoidal function of the osmolality. ProP orthologues share an extended, cytoplasmic C-terminal domain. Orthologues with and without a C-terminal, α-helical coiled-coil domain respond similarly to the osmolality. ProP concentrates at the poles and septa of Escherichia coli cells in a cardiolipin (CL)-dependent manner. The roles of phospholipids and the C-terminal domain in subcellular localization of ProP were explored. Liposome association of peptides representing the C-terminal domains of ProP orthologues and variants in vitro was compared with subcellular localization of the corresponding orthologues and variants in vivo. In the absence of coiled-coil formation, the C-terminal domain bound liposomes and ProP concentrated at the cell poles in a CL-independent manner. The presence of the coiled-coil replaced those phenomena with CL-dependent binding and localization. The effects of amino acid replacements on lipid association of the C-terminal peptide fully recapitulated their effects on the subcellular localization of ProP. These data suggest that polar localization of ProP results from association of its C-terminal domain with the anionic lipid-enriched membrane at the cell poles. The coiled-coil domain present on only some orthologues renders that phenomenon CL-dependent.