Table 2.

Potential stimuli for membrane- or nucleoid-based osmosensorsa

Compartment sampledStimulus detected, change inb:
PeriplasmThickness
Turgor pressure
Concn of a specific cosolvent (e.g., glucan)
Macromolecular crowding
Osmolality
Ionic strength
Cytoplasmic membraneOsmolality gradient
Lateral pressure
Bilayer curvature
Head group charge density
Head group hydrogen bonding
Head group hydration
Thickness
Lateral phospholipid distribution
Intermonolayer phospholipid distribution
CytoplasmOsmolality
Ionic strength
Concn of kosmotropes
Concn of a specific cosolvent (e.g., K glutamate)
Macromolecular crowding or confinement
NucleoidTurgor pressure
Counterion composition
Protein composition
Macromolecular crowding
DNA topology
  • a The entries in this table were deduced by considering the ways in which solvent changes could affect the conformations of osmosensors placed in the cytoplasmic membrane or the nucleoid. A membrane-based osmosensor could sample properties of the periplasmic and/or cytoplasmic solvent as well as characteristics of the membrane itself.

  • b Bold entries are relevant to membrane-based osmosensors that retain their effectiveness in cell, vesicle, and proteoliposome systems (in the absence of exogenous macromolecular crowding agents) (e.g., osmoprotectant transporter ProP, mechanosensitive channel MscL).