A Novel Membrane Protein Capable of Binding the Na+/H+ Antiporter (Nha1p) Enhances the Salinity-resistant Cell Growth of Saccharomyces cerevisiae

Abstract

The Na؉ /H ؉ antiporter Nha1p of Saccharomyces cerevisiae plays an important role in maintaining intracellular pH and Na ؉ homeostasis. Nha1p has a two-domain structure composed of integral membrane and hydrophilic tail regions. Overexpression of a peptide of ϳ40 residues (C1؉C2 domains) that is localized in the juxtamembrane area of its cytoplasmic tail caused cell growth retardation in highly saline conditions, possibly by decreasing Na ؉ /H ؉ antiporter activity. A multicopy suppressor gene of this growth retardation was identified from a yeast genome library. The clone encodes a novel membrane protein denoted as COS3 in the genome data base. Overexpression or deletion of COS3 increases or decreases salinity-resistant cell growth, respectively. However, in nha1⌬ cells, overexpression of COS3 alone did not suppress the growth retardation. Cos3p and a hydrophilic portion of Cos3p interact with the C1؉C2 peptide in vitro, and Cos3p is co-precipitated with Nha1p from yeast cell extracts. Cos3p-GFP mainly resides at the vacuole, but overexpression of Nha1p caused a portion of the Cos3p-GFP proteins to shift to the cytoplasmic membrane. These observations suggest that Cos3p is a novel membrane protein that can enhance salinity-resistant cell growth by interacting with the C1؉C2 domain of Nha1p and thereby possibly activating the antiporter activity of this protein.

Probing the Function of STAS Domains of the Arabidopsis Sulfate Transporters

“…The activity of the mammalian Na ϩ /H ϩ antiporter, NHE1, is regulated negatively by a domain within its carboxyl-terminal cytosolic extension, probably through intramolecular interactions (32), and positively by the binding of a calcineurin B-like protein to the cytosolic extension (33). In a recent study, the Cos3p polypeptide of S. cerevisiae was found to interact with the carboxyl-terminal, juxtamembrane domain of the Na ϩ /H ϩ exchanger Nha1, possibly increasing the activity of this antiporter and enhancing the salinity resistance of cells (34). The STAS domains and linker regions of the sulfate transporters are thought to be important for modulating transporter activity, because sel1-3, sel1-7, and sel1-8 mutations in the linker region between TMD12 and the STAS domain of Sultr1;2 (17) abolish sulfate transport activity with-out interrupting membrane localization of the protein, 2 and mutations within the STAS domains of mammalian sulfate transporter family members cause severe disease phenotypes (6,8,10,11).…”

Dynamic reprogramming of transcription factors to and from the subtelomere

“…Stress-only SBTFs largely targeted alcohol dehydrogenases (AAD3 and ADH7) along with YRF genes, a family of putative helicases located within the subtelomeric Y9 repeated element, which may function in telomere maintenance when telomerase is absent (Yamada et al 1998). Rich-media SBTFs bound YRF genes as well as members of the COS gene family, which are widely conserved and may function in salt resistance (Mitsui et al 2004) and the unfolded protein response (Spode et al 2002) but are otherwise generally uncharacterized.…”

Telomeres in fungi

“…Many, though not all members of the following gene families have arisen via subtelomeric duplication: ADH (NADPHdependent alcohol dehydrogenases), PAU (seripauperins; active during alcoholic fermentation but little understood), and COS (membrane proteins involved in salt resistance (Mitsui et al 2004).…”