Calcineurin is a Ca2+/calmodulin-dependent serine/threonine protein phosphatase conserved from yeast to mammals required for cell survival during environmental stress in yeast. It dephosphorylates several proteins located in different cellular compartments. Hph1 is a substrate of calcineurin that together with Hph2, its homolog, is also required for cellular adaptation to environmental stress. Hph1 and Hph2 are novel proteins of unknown function. Hph1 and Hph2 are tail-anchored integral ER-membrane proteins and have no identifiable homologs of in other organisms, except closely related yeast species. The goal of this work was to identify proteins that interact with Hph1 and Hph2 to help us identify their biological function. We show that Hph1 and Hph2 interact with the post-translational translocation machinery and are required for Vph1 stability, suggesting that they function in post-translational translocation at the ER. We have found several additional phenotypes for cells lacking HPH1 and HPH2 that overlap with the phenotypes observed for cells that have defects in vacuolar acidification. Hph1, but not Hph2, interacts with Vam6, a guanine-nucleotide-exchange factor, that regulates homotypic vacuolar fusion (through Ypt7) and TORC1 activation (through Gtr1). Interestingly, hph1[Delta] hph2[Delta] cells are resistant to rapamycin, further suggesting a role for these proteins in nutrient signaling. Structure-function analyses revealed that the coiled-coil motif is required for proper Hph1 localization and function, whereas the transmembrane domain is dispensable. This study has advanced our understanding of Hph1 and calcineurin function in regulating the cell's response to environmental stress and paves the way for a mechanistic understanding of Hph1 and Hph2 function in yeast.The possible role for Hph1 (and Hph2) in mediating homotypic vacuole fusion should be thoroughly investigated. First, it should be checked whether Hph1 and Hph2 interact with other components of the HOPS complex. The interaction can beanbsp;...
|Title||:||Functional Analyses of HPH1and HPH2 Revealed Roles in Post-translational Protein Translocation and Nutrient Translocation and Nutrient Signaling|
|Author||:||Francisco Javier Pina|
|Publisher||:||Stanford University - 2010|