Helping Hands for Budding Prospects: ENTH/ANTH/VHS Accessory Proteins in Endocytosis, Vacuolar Transport, and Secretion

Abstract

Coated vesicles provide a major mechanism for the transport of proteins through the endomembrane system of plants. Transport between the endoplasmic reticulum and the Golgi involves vesicles with COPI and COPII coats, whereas clathrin is the predominant coat in endocytosis and post-Golgi trafficking. Sorting of cargo, coat assembly, budding, and fission are all complex and tightly regulated processes that involve many proteins. The mechanisms and responsible factors are largely conserved in eukaryotes, and increasing organismal complexity tends to be associated with a greater numbers of individual family members. Among the key factors is the class of ENTH/ANTH/VHS domain-containing proteins, which link membrane subdomains, clathrin, and other adapter proteins involved in early steps of clathrin coated vesicle formation. More than 30 Arabidopsis thaliana proteins contain this domain, but their generally low sequence conservation has made functional classification difficult. Reports from the last two years have greatly expanded our knowledge of these proteins and suggest that ENTH/ANTH/VHS domain proteins are involved in various instances of clathrin-related endomembrane trafficking in plants. This review aims to summarize these new findings and discuss the broader context of clathrin-dependent plant vesicular transport.

EPSIN1 Modulates the Plasma Membrane Abundance of FLAGELLIN SENSING2 for Effective Immune Responses

“…Arabidopsis EPS1 belongs to the ENTH/ANTH/ VHS superfamily of proteins that span across kingdoms, and its members contain an ENTH (EPSIN N-terminal homology), an ANTH (AP180 N-terminal homology), or a VHS (Vps27, Hrs, and STAM) domain at their N terminus (Duncan and Payne, 2003;Legendre-Guillemin et al, 2004;De Craene et al, 2012). The Arabidopsis genome encodes 35 ENTH/ANTH/ VHS domain family members, including six with an ENTH domain referred to as EPS1 to EPS6 (Holstein and Oliviusson, 2005;Zouhar and Sauer, 2014). These six EPSs form a subfamily that is distinct from the divergent ENTH domain-containing MODIFIED TRANSPORT TO THE VACUOLE, with roles in TGN/ EE-to-vacuolar cargo trafficking (Sauer et al, 2013).…”

Differential Regulation of Clathrin and Its Adaptor Proteins during Membrane Recruitment for Endocytosis

“…In plants, CME is essential for many developmental processes, nutrient uptake, and responses to biotic and abiotic stresses or stimuli (Chen et al, 2011;Baisa et al, 2013;Fan et al, 2015;Zhang et al, 2015). In addition to their role in the internalization of PM proteins and associated ligands, distinct clathrin-coated vesicles (CCVs) form at the trans-Golgi network/early endosome (TGN/EE), where the trafficking pathways involved in the transport of newly synthesized proteins to the PM or vacuole, and the delivery of endocytosed proteins from the PM, converge (Song et al, 2006;Viotti et al, 2010;Dettmer and Friml, 2011;Zouhar and Sauer, 2014). The formation of distinct CCVs at the PM and TGN/EE requires the recruitment of clathrin and organellespecific adaptor protein complexes that aid in the temporal and spatial regulation of coated vesicle formation (Holstein, 2002;Lam et al, 2007aLam et al, , 2007bHwang and Robinson, 2009).…”

Sorting of Arabidopsis NRAMP3 and NRAMP4 depends on adaptor protein complex AP4 and a dileucine‐based motif

“…The role of other accessory proteins in vesicle trafficking is just beginning to be illuminated in the plant system. However, several studies have already suggested a role in cargo recognition for A/ENTH domain‐containing proteins like EPSINs, and have already shown that these proteins are able to interact with AP complexes and cargo . TEPSIN/ENTHD2 was recently identified as an accessory protein of animal AP4 .…”

“…However, several studies have already suggested a role in cargo recognition for A/ENTH domain-containing proteins like EPSINs, and have already shown that these proteins are able to interact with AP complexes and cargo. [76][77][78][79] TEPSIN/ENTHD2 was recently identified as an accessory protein of animal AP4. [80][81][82] The closest protein homolog to human TEPSIN in Arabidopsis corresponds to the recently characterized epsin N-terminal homology protein MTV1 (At3g16270).…”