Involvement of the exomer complex in the polarized transport of Ena1 required forSaccharomyces cerevisiaesurvival against toxic cations

Abstract

Here we show that the TGN complex named exomer is required for alkali cation tolerance in yeast because of its roles in the sorting and polarization of the plasma membrane Na+-ATPase Ena1 and on the signal processing through the RIM101 pathway, thus widening the functional repertoire of the yeast exomer.

Monovalent cation transporters at the plasma membrane in yeasts

“…Mutation in diverse vacuolar protein sorting (vps) components, which results in salt sensitivity, does not alter proper Ena1 localization but severely delays the kinetics of accumulation at the plasma membrane (Logg, Warringer, Hashemi, Kall, & Blomberg, ). Recently, Anton and coworkers (Anton et al, ) reported that although Ena1 can reach the plasma membrane independently of the exomer, this structure is required for proper polarized delivery of the ATPase to the bud. These authors also provided evidence indicating that lack of the exomer prevents full induction of the ENA1 gene upon salt stress, likely due to impaired Rim101 processing (see below).…”

Evolutionary cell biology traces the rise of the exomer complex in Fungi from an ancient eukaryotic component

“…A common trait for exomer cargoes appears to be the polarized localization at the plasma membrane 17 , which is maintained by a delicate balance of exo- and endocytosis requiring exomer being in control of TGN export. Overall, our data suggest functional homology of exomer proteins across Saccharomycotina, while also showing differences consistent with the wide evolutionary distance of the taxa in question that probably reflect also the progressive neofunctionalization of ChAPs in the BC8 clade that led to the unique exomer specialization as a cargo adaptor in Saccharomyces .…”

“…Functionality of the heterologous expressed proteins was assessed in a S . cerevisiae chs5∆ mutant based on the chs5∆ phenotypes previously described 17 .…”

“…To date less than a handful of bona fide exclusively exomer-dependent cargoes have been reported (Chs3, Fus1, Pin2) 10 , 15 , 16 , none of which are conserved in mammalian cells. More recently, however, this exclusivity of exomer cargo selection was questioned as some plasma membrane proteins may use either the conventional or the exomer-dependent route 17 . The ion transporter Ena1 is such a protein, because exomer-dependent polarized localization of Ena1 is necessary to counteract toxic cation concentrations 17 , and Ena1 is conserved from yeast to mammals.…”

Papel de los adaptadores de clatrina GGA y Ent3, y de la SNARE Fsv1 en el tráfico entre la red trans del Golgi, el endosoma prevacuolar y la vacuola

“…También facilita el transporte de Fus1 (proteína que participa en fusión celular) hacia la punta de las proyecciones celulares durante el proceso de conjugación (Barfield et al, 2009;Santos and Snyder 2003) . Además, se ha visto que el exómero promueve el transporte polarizado de la bomba de sodio Ena1 hacia la yema de la levadura en gemación (Anton et al, 2017).…”