Quality control of a mutant plasma membrane ATPase: ubiquitylation prevents cell-surface stability.
The plasma membrane ATPase, Pma1, has remarkable longevity at the cell surface. In contrast to the wild-type protein, the temperature-sensitive mutant Pma1-10 is misfolded and undergoes rapid removal from the cell surface for vacuolar degradation. At the restrictive temperature, Pma1-10 becomes ubiquitylated before or upon arrival at the plasma membrane. Internalization from the plasma membrane and vacuolar degradation of Pma1-10 is dependent on the ubiquitin-interacting motif (UIM) of the epsin Ent1, suggesting recognition of ubiquitylated substrate by the endocytic machinery. Surprisingly, ubiquitylation of Pma1-10 is reversed when its internalization is blocked in an end3 mutant. Under these conditions, Pma1-10 acquires association with detergent-insoluble, glycolipid-enriched complexes (DIGs) which has been suggested to promote stability of wild-type Pma1. Ubiquitylation does not cause DIG exclusion because a Pma1-Ub fusion protein is not significantly excluded from DIGs. We suggest that ubiquitylation of Pma1-10 represents a component of a quality control mechanism that targets the misfolded protein for removal from the plasma membrane. Rapid internalization of Pma1-10 caused by its ubiquitylation may preempt establishment of stabilizing interactions.
Liu
Yu
Y
Department of Molecular, Cellular, and Developmental Biology, University of Michigan, 830 N. University, Ann Arbor, MI 48109, USA.
Chang
Amy
A
D002352:Carrier Proteins / Q000378:metabolism; D002462:Cell Membrane / Q000378:metabolism*; D004721:Endoplasmic Reticulum / Q000378:metabolism; D004795:Enzyme Stability; D006180:Proton-Translocating ATPases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000166:cytology / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D025801:Ubiquitin / Q000235:genetics / Q000378:metabolism*; D033921:Vesicular Transport Proteins
D002352:Carrier Proteins; C121319:ENT1 protein, S cerevisiae; D011993:Recombinant Fusion Proteins; D029701:Saccharomyces cerevisiae Proteins; D025801:Ubiquitin; D033921:Vesicular Transport Proteins; C092477:PMA1 protein, S cerevisiae; D006180:Proton-Translocating ATPases