Maturation of the yeast plasma membrane [H+]ATPase involves phosphorylation during intracellular transport.

Abstract

. In this study we show that the plasma membrane [H+]ATPase of Saccharomyces cerevisiae is phosphorylated on multiple Ser and Thr residues in vivo. Phosphorylation occurs during the movement of newly synthesized ATPase from the ER to the cell surface, as revealed by the analysis of temperature-sensitive sec mutants blocked at successive steps of the secretory pathway. Two-dimensional phosphopeptide analysis of the ATPase indicates that, although most sites are phosphorylated at or before arrival in secretory vesi-T HE plasma membrane ATPase ofSaccharomyces cerevisiae is a proton pump that regulates cytoplasmic pH and provides the driving force for nutrient uptake (Serrano et al ., 1986, Serrano, 1989. Not surprisingly, in light of these critical physiologic functions, the [H+]ATPase is essential for cell viability. It has strong structural homology with other EX2 or P-type ATPases involved in maintaining ionic homeostasis, including the [Na+,K+] and Cat+ATPases of mammalian cells. Like other members of its class, the yeast ATPase has a catalytic subunit of -100 kD, hydrolyzes ATP via a transient aspartylphosphate intermediate, and is inhibited by low concentrations of vanadate. Sequence analysis of the PMAI gene encoding the yeast [H+]-ATPase predicts that the protein consists of a large central cytoplasmic domain containing putative sites for ATP binding and hydrolysis, anchored in the membrane by four hydrophobic segments at the NH2-terminal end and four to six hydrophobic segments at the COOH-terminal end .One approach taken in our laboratory to understanding structure-function relationships of the [H+]ATPase has been to study the acquisition of tertiary structure and activity during enzyme biogenesis . Recent work has established that newly synthesized [H+]ATPase becomes integrated into the endoplasmic reticulum membrane without cleavage of an NH2-terminal signal sequence, and is delivered to the cell surface via the secretory pathway (Holcomb et al., 1988) . In sec mutants blocked at discrete steps of the pathway, membrane biogenesis is prevented (Novick and Schekman, 1983 ;Tschopp et al ., 1984), and [H+]ATPase en route to the plasma membrane becomes trapped within the ER, Golgi compartment, or secretory vesicles (Brada and Schekman, 1988) . The ER and Golgi forms of the ATPase have not yet been examined for activity, but the enzyme accumulated in

Lipid-dependent surface transport of the proton pumping ATPase: A model to study plasma membrane biogenesis in yeast

“…As with other integral membrane proteins destined for the plasma membrane, Pma1 is biosynthetically inserted into the membrane of the ER, from where it is transported by vesicular carriers to its final destination [2,3]. Already in the ER, Pma1 forms a large 1.8-MDa homo-oligomeric complex that resists extraction by detergents [4].…”

“…Even though LST1 is not essential, cells lacking LST1 are sensitive to low pH because of a reduced flux of Pma1 out of the ER [5]. During transport, Pma1 is not modified by glycosylation or proteolysis, but the protein becomes phosphorylated on multiple serine and threonine residues [2,3]. The significance of these phosphorylations is still unknown, but there is evidence that at least one of these phosphorylations that occurs at or near the plasma membrane is important for glucose-dependent activation of the enzyme [3,6].…”

Structure, function and regulation of plasma membrane H+‐ATPase

“…Arg-and Thr912 within this terminal region are important for regulation, suggesting a phosphorylation mechanism [ 181. Actually, glucose activation of the ATPase is acompanied by the appearance of a novel phosphopeptide in thermolysin digests of the enzyme [19]. A double mutation at the carboxyl-terminus @erg"+ Ala; Thr912+Ala) greatly reduces the activation of the ATPase by glucose [18].…”

A Role For Lte1p (a Low Temperature Essential Protein Involved in Mitosis) in Proprotein Processing in the Yeast Secretory Pathway

“…All eis mutants impair proprotein processing, resulting in enhanced immunoreactive insulin secretion (1), and expression of full-length mycLte1p restores the insulin secretion to levels seen in wild-type (wt) cells. Western Blot-Steady-state levels of mycLte1p, Ste3-Myc, and Kex2p were analyzed in cell lysates prepared from mid-log cultures by vortexing with glass beads, as described previously (21). Sample loading was normalized to lysate protein as measured by BCA protein assay (Pierce).…”