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Sar1 is a small GTPase of the ARF family. Upon exchange of GDP for GTP, Sar1 associates with the endoplasmic reticulum (ER) membrane and recruits COPII components, orchestrating cargo concentration and membrane deformation. Many aspects of the role of Sar1 and regulation of its GTP cycle remain unclear, especially as complexity increases in higher organisms that secrete a wider range of cargoes. This review focusses on the regulation of GTP hydrolysis and its role in coat assembly, as well as the mechanism of Sar1‐induced membrane deformation and scission. Finally, we highlight the additional specialisation in higher eukaryotes and the outstanding questions on how Sar1 functions are orchestrated. [ABSTRACT FROM AUTHOR]

Abstract: Enterohemorrhagic Escherichia coli (EHEC) and enteropathogenic E. coli (EPEC) are bacterial pathogens that cause severe illnesses in humans. Citrobacter rodentium is a related mouse pathogen that serves as a small animal model for EPEC and EHEC infections. EPEC, EHEC and C. rodentium translocate bacterial virulence proteins directly into host intestinal cells via a type III secretion system (T3SS). Non-LEE-encoded effector A (NleA) is a T3SS effector that is common to EPEC, EHEC and C. rodentium. NleA interacts with and inhibits the mammalian COPII complex, impairing cellular secretion; this interaction is required for bacterial virulence. Although diarrhea is a hallmark of EPEC, EHEC and C. rodentium infections, the underlying mechanisms are not well characterized. One of the essential functions of the intestine is to maintain a barrier between the lumen and submucosa. Tight junctions seal the space between adjacent epithelial cells creating this barrier. Consequently, it is thought that the disruption of intestinal epithelial tight junctions by EPEC, EHEC, and C. rodentium could result in a loss of barrier function. In this study, we demonstrate that NleA mediated COPII inhibition is required for EPEC- and C. rodentium-mediated disruption of tight junction proteins and increases in fecal water content. [Copyright &y& Elsevier]

Membrane and secretory proteins are essential for almost every aspect of cellular function. These proteins are incorporated into ER-derived carriers and transported to the Golgi before being sorted for delivery to their final destination. Although ER-to-Golgi trafficking is highly conserved among eukaryotes, several layers of complexity have been added to meet the increased demands of complex cell types in metazoans. The specialized morphology of neurons and the necessity for precise spatiotemporal control over membrane and secretory protein localization and function make them particularly vulnerable to defects in trafficking. This review summarizes the general mechanisms involved in ER-to-Golgi trafficking and highlights mutations in genes affecting this process, which are associated with neurological diseases in humans. [ABSTRACT FROM AUTHOR]

Autophagy targets cytoplasmic materials for degradation and influences cell health. Organelle contact and trafficking systems provide membranes for autophagosome formation, but how different membrane systems are selected for use during autophagy remains unclear. Here, we report a novel function of the endosomal sorting complex required for transport (ESCRT) in the regulation of endoplasmic reticulum (ER) coat protein complex II (COPII) vesicle formation that influences autophagy. The ESCRT functions in a pathway upstream of Vps13D to influence COPII vesicle transport, ER-Golgi intermediate compartment (ERGIC) assembly, and autophagosome formation. Atg9 functions downstream of the ESCRT to facilitate ERGIC and autophagosome formation. Interestingly, cells lacking either ESCRT or Vps13D functions exhibit dilated ER structures that are similar to cranio-lenticulo-sutural dysplasia patient cells with SEC23A mutations, which encodes a component of COPII vesicles. Our data reveal a novel ESCRT-dependent pathway that influences the ERGIC and autophagosome formation. [Display omitted] • The ESCRT and Vps13D function in a common autophagy pathway • The ESCRT influences ER maturation and COPII trafficking • Vps13D influences COPII trafficking • The ESCRT influences ERGIC and Vps13D availability for Atg9 induction of autophagy The removal of cytoplasmic materials by autophagy is important for cell and organism health. Wang et al. identify a relationship between the endosomal sorting complexes required for transport (ESCRT) and Vps13D in the regulation of endoplasmic reticulum (ER) coat protein complex II (COPII) vesicle formation that influences autophagy. [ABSTRACT FROM AUTHOR]

Abstract: Vacuolar Sorting Determinants (VSDs) have been extensively studied in plants but the mechanisms for the accumulation of storage proteins in somatic tissues are not yet fully understood. In this work we used two mutated versions of well-documented vacuolar fluorescent reporters, a GFP fusion in frame with the C-terminal VSD of tobacco chitinase (GFPChi) and an N-terminal fusion in frame with the sequence-specific VSD of the barley cysteine protease aleurain (AleuGFP). The GFP sequence was mutated to present an N-glycosylation site at the amino-acid position 133. The reporters were transiently expressed in Nicotiana tabacum protoplasts and agroinfiltrated in Nicotiana benthamiana leaves and their distribution was identical to that of the non-glycosylated versions. With the glycosylated GFPs we could highlight a differential ENDO-H sensitivity and therefore differential glycan modifications. This finding suggests two different and independent routes to the vacuole for the two reporters. BFA also had a differential effect on the two markers and further, inhibition of COPII trafficking by a specific dominant-negative mutant (NtSar1h74l) confirmed that GFPChi transport from the ER to the vacuole is not fully dependent on the Golgi apparatus. [Copyright &y& Elsevier]