Structure and function of yeast and fungal Na⁺/H⁺ antiporters

Abstract

Sodium proton antiporters (or sodium proton exchangers [NHEs]) are a critical family of membrane proteins that exchange sodium for protons across cell membranes. In yeast and plants, their primary function is to keep the sodium concentration low inside the cytoplasm. One class of NHE constitutively expressed in yeast is the plasma membrane Na 1 /H 1 antiporter, and another class is expressed on the endosomal/ vacuolar membrane. At present, four bacterial plasma membrane antiporter structures are known and nuclear magnetic resonance structures are available for the membrane spanning transmembrane helices of mammalian and yeast NHEs.Additionally, a vast amount of mutational data are available on the role of individual amino acids and critical motifs involved in transport. We combine this information to obtain a more detailed picture of the yeast NHE plasma membrane protein and review mechanisms of transport, conserved motifs, unique residues important in function, and regulation of these proteins. The Na

Broad phylogenetic analysis of cation/proton antiporters reveals transport determinants

“…3 ). Consistent with our findings, these eight positions were recently proposed to be important for the function and regulation of eukaryotic and archaeal CPA1s, based on a few representatives 38 .…”

“…3b , see also ref. 38 ), while in CPA2s it can feature any residue. Therefore, we refer to it as E 5 when discussing CPA1s and - 5 in the context of CPA2s.…”

Monovalent cation transporters at the plasma membrane in yeasts

“…The function of some of them has also been elucidated by the deletion of the corresponding gene and characterization of phenotypes of resulting mutants (e.g., Schizosaccharomyces pombe , C. albicans , and C. glabrata ; reviewed in Ramos et al, ). S. cerevisiae Nha1 and S. pombe Sod2 (recently renamed to SpNHE1; Dutta & Fliegel, ) are among the first yeast alkali metal cation antiporters to be isolated and characterized, together with those of Zygosaccharomyces rouxii and C. albicans , and are the two best studied yeast antiporters (Ariño et al, ). In fact, SpSod2 was the first yeast transport system with a Na + /H + antiport mechanism characterized.…”

“…The detailed structure of a yeast NHA antiporter has not been elucidated yet, and some predictions have been made using the known crystal structure of several bacterial homologues (e.g., Escherichia coli NhaA; Hunte et al, ). Numerous studies revealed the importance of various amino acid residues, mainly charged or polar ones located in the transmembrane segments, on the antiporter activity and substrate specificity (e.g., Dibrov, Young, & Fliegel, ; Kinclova‐Zimmermannova, Zavrel, & Sychrova, , ; reviewed recently in Dutta & Fliegel, ). Several of these amino acid residues seem to be conserved in the Na + /H + antiporters of all organisms and are proposed to be directly involved in the translocation of ions and protons through the antiporter.…”

“…Several of these amino acid residues seem to be conserved in the Na + /H + antiporters of all organisms and are proposed to be directly involved in the translocation of ions and protons through the antiporter. For S. pombe Sod2/NHE1, alanine scanning approaches or construction of cysteine‐free mutants recently revealed new residues important for antiporter activity and structure (Ullah et al, ; Ullah, El‐Magd, & Fliegel, ) and have led to the proposal of a model with 13 transmembrane segments and an outward‐oriented N‐terminus (Dutta & Fliegel, ). Another approach, identifying the amino acids important for the substrate specificity of yeast antiporters, revealed a group of four amino acid residues located in three different transmembrane segments, which together form a hydrophobic filter whose size determines the substrate specificity.…”