The trehalose protective mechanism during thermal stress in Saccharomyces cerevisiae: The roles of Ath1 and Agt1

Abstract

Trehalose on both sides of the bilayer is a requirement for full protection of membranes against stress. It was not known yet how trehalose, synthesized in the cytosol when dividing Saccharomyces cerevisiae cells are shifted from 28◦C to 40◦C, is transported to the outside and degraded when cells return to 28◦C. According to our results, the lack of Agt1, a trehalose transporter, although had not affected trehalose synthesis, reduced cell tolerance to 51◦C and increased lipid peroxidation. The damage was reversed when external trehalose was added during 40◦C adaptation, confirming that the reason for the agt1 sensitivity is the absence of trehalose at the outside of the lipid bilayer. The 40–28◦C condition caused cytosolic trehalase (Nth1) activation, reducing intracellular trehalose and, consequently, the survival rates after 51◦C. Although lower than nth1 strain, cells deficient in acid trehalase (ath1) maintained increased trehalose levels after 40◦C–28◦C shift, which conferred protection against 51◦C. Both Ath1 and Agt1 were found into vesicles near to plasma membrane in response to stress. This suggests that Agt1 containing vesicles would fuse with the membrane under 40◦C to transport part of the cytosolic trehalose to the outside. By a similar mechanism, Ath1 would reach the cell surface to hydrolyze the external trehalose but only when the stress would be over. Corroborating this conclusion, Ath1 activity in soluble cell-free extracts increased after 40◦C adaptation but decreased when cells returned to 28◦C. During 40◦C, Ath1 is confined into vesicles, avoiding the cleavage of the outside trehalose.