Photodynamic inactivation (PDI) is a non-antibiotic option for the treatment of infectious diseases. Although Gram-positive bacteria have been shown to be highly susceptible to PDI, the inactivation of Gram-negative bacteria has been more challenging due to the impermeability properties of the outer membrane. In the present study, a series of photosensitizers which contain one to four positive charges (1–4) were used to evaluate the charge influence on the PDI of a Gram-negative bacteria, Escherichia coli (E. coli), and their interaction with the cell membrane. The dose-response PDI results confirm the relevance of the number of positive charges on the porphyrin molecule in the PDI of E. coli. The difference between the Hill coefficients of cationic porphyrins with 1–3 positive charges and the tetra-cationic porphyrin (4) revealed potential variations in their mechanism of inactivation. Fluorescent live-cell microscopy studies showed that cationic porphyrins with 1–3 positive charges bind to the cell membrane of E. coli, but are not internalized. On the contrary, the tetra-cationic porphyrin (4) permeates through the membrane of the cells. The contrast in the interaction of cationic porphyrins with E. coli confirmed that they followed different mechanisms of inactivation. This work helps to have a better understanding of the structure-activity relationship in the efficiency of the PDI process of cationic porphyrins against Gram-negative bacteria.

In eukaryotes, lipids are not only an important constituent of the plasma membrane but also used to generate specialized membrane-bound organelles, including temporary compartments with critical functions. As such, lipids play a key role in intracellular homeostasis-the ability of a cell to maintain stable internal conditions upon changes in its extracellular environment. Autophagy, one of the cellular processes through which eukaryotic cells strive for survival under stress, is heavily dependent on lipid and membrane trafficking through the de novo formation of autophagosomes-temporary, large, and double-bilayered organelles in which materials are encapsulated for recycling. This chapter discusses what we know about lipid homeostasis and trafficking during autophagy and autophagosome formation and comments on future directions of the field.

No abstract

The sorting nexins (SNXs), constitute a diverse family of molecules that play varied roles in membrane trafficking, cell signaling, membrane remodeling, organelle motility and autophagy. In particular, the SNX-Bin-Amphiphysin-Rvs (BAR) proteins, a SNX subfamily characterized by a C-terminal dimeric BAR lipid curvature domain and a conserved Phox-homology domain, are of great interest. In budding yeast, many SNX-BAR proteins have well-characterized endo-vacuolar trafficking roles. Phylogenetic analyses allowed us to identify an additional SNX-BAR protein, Vps501, with a novel endovacuolar role. We report that Vps501 uniquely localizes to the vacuolar membrane and has physical and genetic interactions with the SEA complex to regulate TORC1 inactivation. We found cells displayed a severe deficiency in starvation-induced/nonselective autophagy only when SEA complex subunits are ablated in combination with Vps501, indicating a cooperative role with the SEA complex during TORC1 signaling during autophagy induction. Additionally, we found the SEACIT complex becomes destabilized in vps501Δsea1Δ cells, which resulted in aberrant endosomal TORC1 activity and subsequent Atg13 hyperphosphorylation. We have also discovered that the vacuolar localization of Vps501 is dependent upon a direct interaction with Sea1 and a unique lipid binding specificity that is also required for its function.

The sorting nexins (SNX), constitute a diverse family of molecules that play varied roles in membrane trafficking, cell signaling, membrane remodeling, organelle motility and autophagy. In particular, the SNX-BAR proteins, a SNX subfamily characterized by a C-terminal dimeric Bin/Amphiphysin/Rvs (BAR) lipid curvature domain and a conserved Phox-homology domain, are of great interest. In budding yeast, many SNX-BARs proteins have well-characterized endo-vacuolar trafficking roles. Phylogenetic analyses allowed us to identify an additional SNX-BAR protein, Vps501, with a novel endo-vacuolar role. We report that Vps501 uniquely localizes to the vacuolar membrane and works with the SEA complex to regulate autophagy. Furthermore, we found cells displayed a severe deficiency in starvation-induced/nonselective autophagy only when SEA complex subunits are ablated in combination with Vps501, indicating a cooperative role with the SEA complex during autophagy. Additionally, we found the SEA complex becomes destabilized in vps501Δsea1Δ cells, which resulted in aberrant TORC1 hyperactivity and misregulation of autophagy induction.