The structural changes associated to non-photochemical quenching in cyanobacteria is still a matter of discussion. The role of phycobilisome and/or photosystem mobility in this mechanism is a point of interest to be elucidated. Changes in photosystem II fluorescence induced by different quality of illumination (state transitions) or by strong light were characterized at different temperatures in wild-type and mutant cells, that lacked polyunsaturated fatty acids, of the cyanobacterium Synechocystis PCC 6803. The amplitude and the rate of state transitions decreased by lowering temperature in both strains. Our results support the hypothesis that a movement of membrane complexes and/or changes in the oligomerization state of these complexes are involved in the mechanism of state transitions. The quenching induced by strong blue light which was not associated to D1 damage and photoinhibition, did not depend on temperature or on the membrane state. Thus, the mechanism involved in the formation of this type of quenching seems to be unrelated to the movement of membrane complexes. Our results strongly support the idea that the mechanism involved in the fluorescence quenching induced by light 2 is different from that involved in strong blue light induced quenching.

Background & Aims Intraepithelial lymphocytes that express the γδ T cell receptor (γδ IELs) limit pathogen translocation across the intestinal epithelium by unknown mechanisms. We investigated whether γδ IEL migration and interaction with epithelial cells promote mucosal barrier maintenance during enteric infection. Methods Salmonella typhimurium or Toxoplasma gondii were administered to γδ T cell-deficient (Tcrd KO), CD103-deficient (CD103 KO), or control TcrdEGFP C57BL/6 reporter mice. Intravital microscopy was used to visualize migration of GFP-tagged γδ T cells within the small intestinal mucosa of mice infected with DsRed-labeled S typhimurium. Mixed bone marrow chimeras were generated to assess the effects of γδ IEL migration on early pathogen invasion and chronic systemic infection. Results Morphometric analyses of intravital video microscopy data showed that γδ IELs rapidly localized to and remained near epithelial cells in direct contact with bacteria. Within 1 hr, greater numbers of T gondii or S typhimurium were present within mucosae of mice with migration-defective occludin KO γδ T cells, compared with controls. Pathogen invasion in Tcrd KO mice was quantitatively similar to that in mice with occludin-deficient γδ T cells, whereas invasion in CD103 KO mice, which have increased migration of γδ T cells into the lateral intercellular space, was reduced by 63%. Consistent with a role of γδ T cell migration in early host defense, systemic salmonellosis developed more rapidly and with greater severity in mice with occludin-deficient γδ IELs, relative to those with wild-type or CD103 KO γδ IELs. Conclusions In mice, intraepithelial migration to epithelial cells in contact with pathogens is essential to γδ IEL surveillance and immediate host defense. γδ IEL occludin is required for early surveillance that limits systemic disease.

The human malaria parasite Plasmodium falciparum relies on the acquisition of host purines for its survival within human erythrocytes. Purine salvage by the parasite requires specialized transporters at the parasite plasma membrane (PPM), but the exact mechanism of purine entry into the infected erythrocyte, and the primary purine source used by the parasite, remain unknown. Here, we report that transgenic parasites lacking the PPM transporter PfNT1 (P. falciparum nucleoside transporter 1) are auxotrophic for hypoxanthine, inosine, and adenosine under physiological conditions and are viable only if these normally essential nutrients are provided at excess concentrations. Transport measurements across the PPM revealed a severe reduction in hypoxanthine uptake in the knockout, whereas adenosine and inosine transport were only partially affected. These data provide compelling evidence for a sequential pathway for exogenous purine conversion into hypoxanthine using host enzymes followed by PfNT1-mediated transport into the parasite. The phenotype of the conditionally lethal mutant establishes PfNT1 as a critical component of purine salvage in P. falciparum and validates PfNT1 as a potential therapeutic target.conditional knockout ͉ sequential pathway ͉ transporter M alaria is one of the foremost threats to human health in the tropical regions of the world (1). The disease is especially challenging to treat because of the widespread emergence of drug-resistant parasites and the limited number of available antimalarial drugs. Consequently, better antimalarial therapies are urgently needed. Plasmodium falciparum, the causative agent of the most deadly form of human malaria, exhibits a complex life cycle that involves both an invertebrate vector, the anopheline mosquito, and humans. Although the ability of the parasite to invade human RBCs provides it with an ideal refuge from immune attacks, RBCs are deficient in various nutrients required for parasite survival and multiplication. Therefore, the parasite has evolved novel transport machineries and specialized enzymes to acquire and metabolize host nutrients. Perhaps most striking is the nutritional requirement for purines. Unlike mammalian cells that synthesize purines de novo, P. falciparum is incapable of purine biosynthesis and has consequently evolved a unique complement of purine salvage enzymes that enable the parasite to scavenge host purines (2-4). The first step in purine acquisition entails the uptake of purines from the host milieu. Because of the essential function of purine salvage in parasite growth and multiplication, purine transporters are regarded as ideal targets for the development of novel therapeutic strategies to combat malaria (5).Although it is known that the movement of purine across the parasite plasma membrane (PPM) requires specialized purine transporters (6), the pathways of purine translocation between the intracellular parasite and the host environment are unknown. Uninfected RBCs express a high-affinity human equilibrative nucleoside tr...

g Toxoplasma gondii is a protozoan parasite that can damage the human brain and eyes. There are no curative medicines. Herein, we describe our discovery of N-benzoyl-2-hydroxybenzamides as a class of compounds effective in the low nanomolar range against T. gondii in vitro and in vivo. Our lead compound, QQ-437, displays robust activity against the parasite and could be useful as a new scaffold for development of novel and improved inhibitors of T. gondii. Our genome-wide investigations reveal a specific mechanism of resistance to N-benzoyl-2-hydroxybenzamides mediated by adaptin-3␤, a large protein from the secretory protein complex. N-Benzoyl-2-hydroxybenzamide-resistant clones have alterations of their secretory pathway, which traffics proteins to micronemes, rhoptries, dense granules, and acidocalcisomes/plant-like vacuole (PLVs). N-Benzoyl-2-hydroxybenzamide treatment also alters micronemes, rhoptries, the contents of dense granules, and, most markedly, acidocalcisomes/PLVs. Furthermore, QQ-437 is active against chloroquine-resistant Plasmodium falciparum. Our studies reveal a novel class of compounds that disrupts a unique secretory pathway of T. gondii, with the potential to be used as scaffolds in the search for improved compounds to treat the devastating diseases caused by apicomplexan parasites.T oxoplasma gondii is an apicomplexan, intracellular parasite that infects one third to one half of the world's population. It can cause eye and brain disease and death, and the presence of infection has been correlated with a variety of neurologic illnesses. Moreover, it is the most frequent cause of infectious uveitis worldwide. Disease can be especially severe in immunocompromised persons and in those infected congenitally (28).There is no perfect treatment for T. gondii infection in humans, as the few available medicines are limited by their side effects and target only the rapidly proliferating tachyzoite form of the parasite. Pyrimethamine and sulfadiazine, which are effective against the tachyzoite form, are currently used to treat active disease. However, treatment with these medicines can be associated with toxicity and hypersensitivity (29), and they do not eradicate the bradyzoite form of the parasite, which remains latent. There are few secondary medicines, and some of them have a delayed mechanism of killing the tachyzoites. No medicines have been reported to be effective against the latent, encysted bradyzoite stage. T. gondii remains in a person's body throughout life, leading to a risk for recurrence of active infection. Novel, effective, and nontoxic antiToxoplasma agents are urgently needed. Herein, we present a series of experiments to identify new lead compounds effective against T. gondii and to begin to understand how they act on this parasite. MATERIALS AND METHODSParasites and cell culture. Confluent monolayers of human foreskin fibroblasts (HFF) were maintained in Iscove's modified Dulbecco's medium supplemented with 10% fetal bovine serum, 1% Glutamax, and 1% penicillin-streptomycin-amp...