Regulation of Saccharomyces cerevisiae Plasma membrane H+-ATPase (Pma1) by Dextrose and Hsp30 during Exposure to Thermal Stress

Pma1p is an essential plasma membrane H+-pump in Saccharomyces cerevisiae that pumps out H+ at the expense of cellular ATP. Its activity is induced by glucose at 30A degrees C and is inhibited by Hsp30 during exposure to heat shock conditions. To further investigate the regulation of Pma1 function by glucose and Hsp30 during exposure to thermal stress, we estimated Pma1 activity, its protein levels and ser-phosphorylation status in membrane fractions isolated from BY4741 and hsp30 Delta cells grown in dextrose and sorbitol at 30A degrees C, and following exposure at 40A degrees C for 30 min. Our results demonstrate that Pma1 activity and protein levels were reduced in Hsp30(+) cells following exposure to thermal stress in dextrose media. The above was not observed in hsp30 Delta cells wherein Pma1 activity did not decrease following exposure to similar conditions. Although Pma1p levels decreased in heat-shocked hsp30 Delta cells, it was lower compared to that observed in Hsp30(+) cells. Total ser-phosphorylation of Pma1 also showed a decrease following exposure to heat shock condition in dextrose media in both BY4741 and hsp30 Delta cells. Its levels were also reduced in BY4741 cells upon heat shock treatment in sorbitol unlike that observed in hsp30 Delta cells wherein it was increased. Taken together the above indicate that heat shock induced reduction in Pma1 activity and protein levels in dextrose media required Hsp30. To examine functional interactions between dextrose utilization, Hsp30 and the regulation of various aspects of Pma1, we determined if dextrose regulated other functions attributed to Hsp30. Results demonstrate that the deletion of HSP30 rendered cells dependent on dextrose utilization for survival during exposure to lethal heat stress. Our study has hence been able to establish a functional relationship between glucose utilization, Hsp30 function and the regulation of Pma1 activity. Finally, since the deletion of HSP30 renders Pma1p levels and its activity unresponsive to thermal stress in dextrose media, we concluded that Hsp30 is necessary to maintain Pma1 in a regulation competent conformation. Hsp30 may thus act as a chaperone in the S. cerevisiae plasma membrane.