Recruitment of Irgb6 to the membrane is a direct trigger for membrane deformation

Irgb6 is a member of interferon gamma-induced immunity related GTPase (IRG), and one of twenty "effector" IRGs, which coordinately attack parasitophorous vacuole membrane (PVM), causing death of intracellular pathogen. Although Irgb6 plays a pivotal role as a pioneer in the process of PVM disruption, the direct effect of Irgb6 on membrane remained to be elucidated. Here, we utilized artificial lipid membranes to reconstitute Irgb6-membrane interaction in vitro, and revealed that Irgb6 directly deformed the membranes. Liposomes incubated with recombinant Irgb6 were drastically deformed generating massive tubular protrusions in the absence of guanine nucleotide, or with GMP-PNP. Liposome deformation was abolished by incubating with Irgb6-K275A/R371A, point mutations at membrane targeting residues. The membrane tubules generated by Irgb6 were mostly disappeared by the addition of GTP or GDP, which are caused by detachment of Irgb6 from membrane. Binding of Irgb6 to the membrane, which was reconstituted in vitro using lipid monolayer, was stimulated at GTP-bound state. Irgb6 GTPase activity was stimulated by the presence of liposomes more than eightfold. Irgb6 GTPase activity in the absence of membrane was also slightly stimulated, by lowering ionic strength, or by increasing protein concentration, indicating synergistic stimulation of the GTPase activity. These results suggest that membrane targeting of Irgb6 and resulting membrane deformation does not require GTP, but converting into GTP-bound state is crucial for detaching Irgb6 from the membrane, which might coincident with local membrane disruption

The Lipid-Binding Defective Dynamin 2 Mutant in Charcot-Marie-Tooth Disease Impairs Proper Actin Bundling and Actin Organization in Glomerular Podocytes

Dynamin is an endocytic protein that functions in vesicle formation by scission of invaginated membranes. Dynamin maintains the structure of foot processes in glomerular podocytes by directly and indirectly interacting with actin filaments. However, molecular mechanisms underlying dynamin-mediated actin regulation are largely unknown. Here, biochemical and cell biological experiments were conducted to uncover how dynamin modulates interactions between membranes and actin in human podocytes. Actin-bundling, membrane tubulating, and GTPase activities of dynamin were examined in vitro using recombinant dynamin 2-wild-type (WT) or dynamin 2-K562E, which is a mutant found in Charcot-Marie-Tooth patients. Dynamin 2-WT and dynamin 2-K562E led to the formation of prominent actin bundles with constant diameters. Whereas liposomes incubated with dynamin 2-WT resulted in tubule formation, dynamin 2-K562E reduced tubulation. Actin filaments and liposomes stimulated dynamin 2-WT GTPase activity by 6- and 20-fold, respectively. Actin-filaments, but not liposomes, stimulated dynamin 2-K562E GTPase activity by 4-fold. Self-assembly-dependent GTPase activity of dynamin 2-K562E was reduced to one-third compared to that of dynamin 2-WT. Incubation of liposomes and actin with dynamin 2-WT led to the formation of thick actin bundles, which often bound to liposomes. The interaction between lipid membranes and actin bundles by dynamin 2-K562E was lower than that by dynamin 2-WT. Dynamin 2-WT partially colocalized with stress fibers and actin bundles based on double immunofluorescence of human podocytes. Dynamin 2-K562E expression resulted in decreased stress fiber density and the formation of aberrant actin clusters. Dynamin 2-K562E colocalized with alpha-actinin-4 in aberrant actin clusters. Reformation of stress fibers after cytochalasin D-induced actin depolymerization and washout was less effective in dynamin 2-K562E-expressing cells than that in dynamin 2-WT. Bis-T-23, a dynamin self-assembly enhancer, was unable to rescue the decreased focal adhesion numbers and reduced stress fiber density induced by dynamin 2-K562E expression. These results suggest that the low affinity of the K562E mutant for lipid membranes, and atypical self-assembling properties, lead to actin disorganization in HPCs. Moreover, lipid-binding and self-assembly of dynamin 2 along actin filaments are required for podocyte morphology and functions. Finally, dynamin 2-mediated interactions between actin and membranes are critical for actin bundle formation in HPCs

Dynamin 1 is important for microtubule organization and stabilization in glomerular podocytes

Dynamin 1 is a neuronal endocytic protein that participates in vesicle formation by scission of invaginated membranes. Dynamin 1 is also expressed in the kidney; however, its physiological significance to this organ remains unknown. Here, we show that dynamin 1 is crucial for microtubule organization and stabilization in glomerular podocytes. By immunofluorescence and immunoelectron microscopy, dynamin 1 was concentrated at microtubules at primary processes in rat podocytes. By immunofluorescence of differentiated mouse podocytes (MPCs), dynamin 1 was often colocalized with microtubule bundles, which radially arranged toward periphery of expanded podocyte. In dynamin 1-depleted MPCs by RNAi, alpha-tubulin showed a dispersed linear filament-like localization, and microtubule bundles were rarely observed. Furthermore, dynamin 1 depletion resulted in the formation of discontinuous, short acetylated alpha-tubulin fragments, and the decrease of microtubule-rich protrusions. Dynamins 1 and 2 double-knockout podocytes showed dispersed acetylated alpha-tubulin and rare protrusions. In vitro, dynamin 1 polymerized around microtubules and cross-linked them into bundles, and increased their resistance to the disassembly-inducing reagents Ca(2+)and podophyllotoxin. In addition, overexpression and depletion of dynamin 1 in MPCs increased and decreased the nocodazole resistance of microtubules, respectively. These results suggest that dynamin 1 supports the microtubule bundle formation and participates in the stabilization of microtubules

Characterization of Naturally Acquired Immunity to a Panel of Antigens Expressed in Mature P. falciparum Gametocytes.

INTRODUCTION: Naturally acquired immune responses against antigens expressed on the surface of mature gametocytes develop in individuals living in malaria-endemic areas. Evidence suggests that such anti-gametocyte immunity can block the development of the parasite in the mosquito, thus playing a role in interrupting transmission. A better comprehension of naturally acquired immunity to these gametocyte antigens can aid the development of transmission-blocking vaccines and improve our understanding of the human infectious reservoir. METHODS: Antigens expressed on the surface of mature gametocytes that had not previously been widely studied for evidence of naturally acquired immunity were identified for protein expression alongside Pfs230-C using either the mammalian HEK293E or the wheat germ cell-free expression systems. Where there was sequence variation in the candidate antigens (3D7 vs a clinical isolate PfKE04), both variants were expressed. ELISA was used to assess antibody responses against these antigens, as well as against crude stage V gametocyte extract (GE) and AMA1 using archived plasma samples from individuals recruited to participate in malaria cohort studies. We analyzed antibody levels (estimated from optical density units using a standardized ELISA) and seroprevalence (defined as antibody levels greater than three standard deviations above the mean levels of a pool of malaria naïve sera). We described the dynamics of antibody responses to these antigens by identifying factors predictive of antibody levels using linear regression models. RESULTS: Of the 25 antigens selected, seven antigens were produced successfully as recombinant proteins, with one variant antigen, giving a total of eight proteins for evaluation. Antibodies to the candidate antigens were detectable in the study population (N = 216), with seroprevalence ranging from 37.0% (95% CI: 30.6%, 43.9%) for PSOP1 to 77.8% (95% CI: 71.6%, 83.1%) for G377 (3D7 variant). Responses to AMA1 and GE were more prevalent than those to the gametocyte proteins at 87.9% (95% CI: 82.8%, 91.9%) and 88.3% (95% CI: 83.1%, 92.4%), respectively. Additionally, both antibody levels and breadth of antibody responses were associated with age and concurrent parasitaemia. CONCLUSION: Age and concurrent parasitaemia remain important determinants of naturally acquired immunity to gametocyte antigens. Furthermore, we identify novel candidates for transmission-blocking activity evaluation

Blood-stage malaria vaccines: post-genome strategies for the identification of novel vaccine candidates

Introduction: An efficacious malaria vaccine is necessary to advance the current control measures towards malaria elimination. To-date, only RTS,S/AS01, a leading pre-erythrocytic stage vaccine completed phase 3 trials, but with an efficacy of 28–36% in children, and 18–26% in infants, that waned over time. Blood-stage malaria vaccines protect against disease, and are considered effective targets for the logical design of next generation vaccines to improve the RTS,S field efficacy. Therefore, novel blood-stage vaccine candidate discovery efforts are critical, albeit with several challenges including, high polymorphisms in vaccine antigens, poor understanding of targets of naturally protective immunity, and difficulties in the expression of high AT-rich plasmodial proteins. Areas covered: PubMed (www.ncbi.nlm.nih.gov/pubmed) was searched to review the progress and future prospects of malaria vaccine research and development. We focused on post-genome vaccine candidate discovery, malaria vaccine development, sequence diversity, pre-clinical and clinical trials. Expert commentary: Post-genome high-throughput technologies using wheat germ cell-free protein synthesis technology and immuno-profiling with sera from malaria patients with clearly defined outcomes are highlighted to overcome current challenges of malaria vaccine candidate discovery

Correlation between Excited-State Intramolecular Proton-Transfer and Singlet-Oxygen Quenching Activities in 1‑(Acylamino)anthraquinones

Excited-state intramolecular proton-transfer (ESIPT) and singlet-oxygen (¹O₂) quenching activities of intramolecularly hydrogen-bonded 1-(acylamino)­anthraquinones have been studied by means of static and laser spectroscopies. The ESIPT shows a substituent effect, which can be explained in terms of the nodal-plane model. The ESIPT activity positively and linearly correlates with their ¹O₂ quenching activity. The reason for this correlation can be understood by considering ESIPT-induced distortion of their ground-state potential surface and their encounter complex formation with ¹O₂. Intramolecularly hydrogen-bonded hydroxyanthraquinones found in aloe also show a similar positive and linear correlation, which can be understood in the same way

GATS tag system is compatible with biotin labelling methods for protein analysis

Abstract Polypeptide tags and biotin labelling technologies are widely used for protein analyses in biochemistry and cell biology. However, many peptide tag epitopes contain lysine residues (or amino acids) that are masked after biotinylation. Here, we propose the GATS tag system without a lysine residue and with high sensitivity and low non-specific binding using a rabbit monoclonal antibody against Plasmodium falciparum glycosylphosphatidylinositol (GPI)-anchored micronemal antigen (PfGAMA). From 14 monoclonal clones, an Ra3 clone was selected as it recognized an epitope—TLSVGVQNTF—without a lysine residue; this antibody and epitope tag set was called the GATS tag system. Surface plasmon resonance analysis showed that the tag system had a high affinity of 8.71 × 10–9 M. GATS tag indicated a very low background with remarkably high sensitivity and specificity in immunoblotting using the lysates of mammalian cells. It also showed a high sensitivity for immunoprecipitation and immunostaining of cultured human cells. The tag system was highly sensitive in both biotin labelling methods for proteins using NHS-Sulfo-biotin and BioID (proximity-dependent biotin identification) in the human cells, as opposed to a commercially available tag system having lysine residues, which showed reduced sensitivity. These results showed that the GATS tag system is suitable for methods such as BioID involving labelling lysine residues