Mj. Tamas et al., Fps1p controls the accumulation and release of the compatible solute glycerol in yeast osmoregulation, MOL MICROB, 31(4), 1999, pp. 1087-1104
The accumulation of compatible solutes, such as glycerol, in the yeast Sacc
haromyces cerevisiae, is a ubiquitous mechanism in cellular osmoregulation.
Here, we demonstrate that yeast cells control glycerol accumulation in par
t via a regulated, Fps1 p-mediated export of glycerol. Fps1 p is a member o
f the MIP family of channel proteins most closely related to the bacterial
glycerol facilitators. The protein is localized in the plasma membrane. The
physiological role of Fps1 p appears to be glycerol export rather than upt
ake. Fps1 Delta mutants are sensitive to hypo-osmotic shock, demonstrating
that osmolyte export is required for recovery from a sudden drop in externa
l osmolarity, In wild-type cells, the glycerol transport rate is decreased
by hyperosmotic shock and increased by hypo-osmotic shock on a subminute ti
me scale. This regulation seems to be independent of the known yeast osmo-s
ensing HOG and PKC signalling pathways. Mutants lacking the unique hydrophi
lic N-terminal domain of Fps1p, or certain parts thereof, fail to reduce th
e glycerol transport rate after a hyperosmotic shock. Yeast cells carrying
these constructs constitutively release glycerol end show a dominant hypero
smosensitivity, but compensate for glycerol loss after prolonged incubation
by glycerol overproduction. Fps1p may be an example of a more widespread c
lass of regulators of osmoadaptation, which control the cellular content an
d release of compatible solutes.