α-Arrestins, also called arrestin-related trafficking adaptors (ARTs), constitute a large family of proteins conserved from yeast to humans. Despite their evolutionary precedence over their extensively studied relatives of the β-arrestin family, α-arrestins have been discovered relatively recently, and thus their properties are mostly unexplored. The predominant function of α-arrestins is the selective identification of membrane proteins for ubiquitination and degradation, which is an important element in maintaining membrane protein homeostasis as well as global cellular metabolisms. Among members of the arrestin clan, only α-arrestins possess PY motifs that allow canonical binding to WW domains of Rsp5/NEDD4 ubiquitin ligases and the subsequent ubiquitination of membrane proteins leading to their vacuolar/lysosomal degradation. The molecular mechanisms of the selective substrate’s targeting, function, and regulation of α-arrestins in response to different stimuli remain incompletely understood. Several functions of α-arrestins in animal models have been recently characterized, including redox homeostasis regulation, innate immune response regulation, and tumor suppression. However, the molecular mechanisms of α-arrestin regulation and substrate interactions are mainly based on observations from the yeast Saccharomyces cerevisiae model. Nonetheless, α-arrestins have been implicated in health disorders such as diabetes, cardiovascular diseases, neurodegenerative disorders, and tumor progression, placing them in the group of potential therapeutic targets.

In the face of flourishing industrialization and global trade, heavy metal and metalloid contamination of the environment is a growing concern throughout the world. The widespread presence of highly toxic compounds of arsenic, antimony, and cadmium in nature poses a particular threat to human health. Prolonged exposure to these toxins has been associated with severe human diseases, including cancer, diabetes, and neurodegenerative disorders. These toxins are known to induce analogous cellular stresses, such as DNA damage, disturbance of redox homeostasis, and proteotoxicity. To overcome these threats and improve or devise treatment methods, it is crucial to understand the mechanisms of cellular detoxification in metal and metalloid stress. Membrane proteins are key cellular components involved in the uptake, vacuolar/lysosomal sequestration, and efflux of these compounds; thus, deciphering the multilevel regulation of these proteins is of the utmost importance. In this review, we summarize data on the mechanisms of arsenic, antimony, and cadmium detoxification in the context of membrane proteome. We used yeast Saccharomyces cerevisiae as a eukaryotic model to elucidate the complex mechanisms of the production, regulation, and degradation of selected membrane transporters under metal(loid)-induced stress conditions. Additionally, we present data on orthologues membrane proteins involved in metal(loid)-associated diseases in humans.

Arsenic contamination poses a major environmental and public health challenge. In liverworts and ferns, ACR3 transporters mediate arsenite efflux and contribute to arsenic tolerance. We recently showed that ACR3 from Marchantia polymorpha (MpACR3) contains an extended N-terminal region that couples arsenic sensing to membrane trafficking. However, the function and regulation of ACR3 transporters across photosynthetic lineages remain unclear. Here, we characterize ACR3 transporters from phylogenetically distant algae and land plants using heterologous expression in yeast. All examined ACR3 proteins function as arsenic efflux transporters but display two distinct trafficking modes: constitutive plasma membrane localization or metalloid-driven relocalization from the endomembrane system. Like the previously characterized MpACR3, we show that this inducible trafficking is governed by an extended N-terminal domain unique to plant ACR3 proteins, integrating a conserved di-arginine ER/Golgi retention signal with cysteine-based arsenic sensing. These findings establish a direct mechanistic link between metalloid perception and subcellular targeting. Functional assays in Arabidopsis thaliana demonstrated that Physcomitrium patens ACR3 confers arsenic tolerance, reduces root arsenic accumulation, and retains metalloid-dependent trafficking, supporting its physiological relevance. Together, our findings uncover a conserved mechanism linking arsenic sensing to ACR3 trafficking and provide new insight into the evolution of arsenic tolerance in plants. Summary statement: Plant ACR3 transporters mediate arsenic efflux and exhibit distinct trafficking modes. An N-terminal domain links arsenic sensing to the endomembrane system-plasma membrane relocalization, revealing a conserved mechanism controlling ACR3 function and arsenic tolerance across plant lineages.

Arsenic, a toxic and carcinogenic metalloid, is a pervasive environmental contaminant that threatens human health through contaminated water and food. The efflux of As(III) via ACR3 transporters is an ancient detoxification mechanism conserved across prokaryotes, fungi, and plants, with the notable exception of angiosperms. Despite their evolutionary significance, plant ACR3s remain largely uncharacterized. Here, we demonstrate that MpACR3, the ACR3 orthologue from the liverwort Marchantia polymorpha, functions as a metalloid/proton antiporter, conferring resistance to arsenicals and moderate tolerance to antimony. Additionally, we uncover an arsenic-sensing domain within MpACR3 that regulates its intracellular trafficking. Under normal conditions, MpACR3 sorting to the plasma membrane is delayed, resulting in its retention within Golgi bodies. However, As(III) binding to three cysteine residues in the N-terminal cytosolic domain induces a conformational change that facilitates MpACR3 trafficking to the plasma membrane. Furthermore, mutational analysis of a conserved arginine-based motif reveals that the N-terminal domain not only controls MpACR3 accumulation at the plasma membrane but also modulates its transport activity. Importantly, this arsenic-sensing domain is conserved among plant ACR3 transporters, suggesting a plant-specific adaptation to arsenic toxicity.

Arsenic is a toxic, carcinogenic metalloid that threatens human health through contaminated water and food. Arsenite [As(III)] efflux mediated by ACR3 transporters is an ancient detoxification mechanism conserved across prokaryotes, fungi, algae, and non-angiosperm land plants, yet plant ACR3 proteins remain poorly characterized. Here, we show that MpACR3, the ACR3 ortholog from the model liverwort Marchantia polymorpha, contains an arsenic-responsive N-terminal domain that regulates intracellular trafficking. Under nonstress conditions, MpACR3 is detected in Golgi bodies as well as at the plasma membrane (PM) in plant cells, whereas As(III) promotes its relocalization to the PM. As(III) interacts with a cysteine-rich N-terminal region and stabilizes this domain, as shown by arsenite-biotin competition and increased protease resistance. Together with molecular dynamics simulations, which predict As(III)-dependent changes in secondary structure and surface properties, these findings support a model in which ligand-induced remodeling of the N-terminus modulates MpACR3 retention and trafficking. We further identify a di-arginine-containing LRCRF motif in which leucine and arginine residues are required for intracellular retention, whereas cysteine and phenylalanine residues are required for As(III)-induced relocalization to the PM. The broad conservation of related N-terminal domains in plant ACR3 transporters suggests that arsenic-regulated trafficking is a conserved plant adaptation to arsenic toxicity.