Pun1p is a metal ion-inducible, calcineurin/Crz1p-regulated plasma membrane protein required for cell wall integrity

Abstract

Under conditions of environmental stress, the plasma membrane is involved in several regulatory processes to promote cell survival, like maintenance of signaling pathways, cell wall organization and intracellular ion homeostasis. PUN1 encodes a plasma membrane protein localizing to the ergosterol-rich membrane compartment occupied also by the arginine permease Can1. We found that the PUN1 (YLR414c) gene is transcriptionally induced upon metal ion stress. Northern blot analysis of the transcriptional regulation of PUN1 showed that the calcium dependent transcription factor Crz1p is required for PUN1 induction upon heavy metal stress. Here we report that mutants deleted for PUN1 exhibit increased metal ion sensitivity and morphological abnormalities. Microscopical and ultrastructural observations revealed a severe cell wall defect of pun1∆ mutants. By using chemical cross-linking, Blue native electrophoresis, and co-immunoprecipitation we found that Pun1p forms homo-oligomeric protein complexes. We propose that Pun1p is a stress-regulated factor required for cell wall integrity, thereby expanding the functional significance of lateral plasma membrane compartments.

Phenotypic characterization and comparative transcriptomics of evolved Saccharomyces cerevisiae strains with improved tolerance to lignocellulosic derived inhibitors

“…Integrity of cell walls and membranes are important for cells under stress from biomass-derived inhibitors as these target and disrupt these cellular structures [ 19 ]. CHS5 , FLC1 , PIR1, and PUN1 are important for cell wall biosynthesis and functioning [ 63 – 67 ]. HES1 encodes a protein that is assumed to be involved in the regulation of the biosynthesis of ergosterol, an important component of yeast cell membranes, which has been shown to be important for the tolerance of various inhibitory compounds, particularly vanillin [ 29 , 68 , 69 ].…”

MCC/Eisosomes Regulate Cell Wall Synthesis and Stress Responses in Fungi

“…Although in S. cerevisiae a sur7 ∆ mutation causes weaker phenotypes than in C. albicans , related observations have been reported, such as greater susceptibility to osmotic stress [ 125 ]. Other work with S. cerevisiae demonstrated that Pun1, a paralog of Sur7, is induced upon cell wall damage, and pun1 ∆ mutant cells have modified cell walls [ 126 ]. The pun1 ∆ cells are more sensitive to the cell wall degrading enzyme zymolyase, which correlates with other results indicating that the mutant cells have reduced levels of 1,3-β- d -glucans and mannoproteins [ 126 ].…”

“…Other work with S. cerevisiae demonstrated that Pun1, a paralog of Sur7, is induced upon cell wall damage, and pun1 ∆ mutant cells have modified cell walls [ 126 ]. The pun1 ∆ cells are more sensitive to the cell wall degrading enzyme zymolyase, which correlates with other results indicating that the mutant cells have reduced levels of 1,3-β- d -glucans and mannoproteins [ 126 ]. Eisosomes have also been shown to play a role in surviving hypo-osmotic stress in S. pombe protoplasts [ 23 ].…”

Calcium and Cell Response to Heavy Metals: Can Yeast Provide an Answer?

“…A more subtle Mn 2+ -Ca 2+ interplay exists though, being manifested at several levels [41]. For example, high Mn 2+ is controlled by calcineurin/Crz1pregulated Pmr1p and Pun1p [100]. Importantly, the tolerance of yeast cells to Mn 2+ is related to both Pmr1p and Vcx1p [41,64,65,101] two determinants of maintaining low [Ca 2+ ] cyt by transporting the ions to the vacuole and Golgi/ER, respectively [60][61][62][63].…”