Evolution, Composition, Assembly, and Function of the Conoid in Apicomplexa.

The phylum Apicomplexa has been defined by the presence of the apical complex, a structure composed of secretory organelles and specific cytoskeletal elements. A conspicuous feature of the apical complex in many apicomplexans is the conoid, a hollow tapered barrel structure composed of tubulin fibers. In Toxoplasma gondii, the apical complex is a central site of convergence for calcium-related and lipid-mediated signaling pathways that coordinate conoid protrusion, microneme secretion, and actin polymerization, to initiate gliding motility. Through cutting-edge technologies, great progress has recently been made in discovering the structural subcomponents and proteins implicated in the biogenesis and stability of the apical complex and, in turn, these discoveries have shed new light on the function and evolution of this definitive structure

Dual Targeting of Antioxidant and Metabolic Enzymes to the Mitochondrion and the Apicoplast of Toxoplasma gondii

Toxoplasma gondii is an aerobic protozoan parasite that possesses mitochondrial antioxidant enzymes to safely dispose of oxygen radicals generated by cellular respiration and metabolism. As with most Apicomplexans, it also harbors a chloroplast-like organelle, the apicoplast, which hosts various biosynthetic pathways and requires antioxidant protection. Most apicoplast-resident proteins are encoded in the nuclear genome and are targeted to the organelle via a bipartite N-terminal targeting sequence. We show here that two antioxidant enzymes—a superoxide dismutase (TgSOD2) and a thioredoxin-dependent peroxidase (TgTPX1/2)—and an aconitase are dually targeted to both the apicoplast and the mitochondrion of T. gondii. In the case of TgSOD2, our results indicate that a single gene product is bimodally targeted due to an inconspicuous variation within the putative signal peptide of the organellar protein, which significantly alters its subcellular localization. Dual organellar targeting of proteins might occur frequently in Apicomplexans to serve important biological functions such as antioxidant protection and carbon metabolism

Functional Dissection of the Apicomplexan Glideosome Molecular Architecture

SummaryThe glideosome of apicomplexan parasites is an actin- and myosin-based machine located at the pellicle, between the plasma membrane (PM) and inner membrane complex (IMC), that powers parasite motility, migration, and host cell invasion and egress. It is composed of myosin A, its light chain MLC1, and two gliding-associated proteins, GAP50 and GAP45. We identify GAP40, a polytopic protein of the IMC, as an additional glideosome component and show that GAP45 is anchored to the PM and IMC via its N- and C-terminal extremities, respectively. While the C-terminal region of GAP45 recruits MLC1-MyoA to the IMC, the N-terminal acylation and coiled-coil domain preserve pellicle integrity during invasion. GAP45 is essential for gliding, invasion, and egress. The orthologous Plasmodium falciparum GAP45 can fulfill this dual function, as shown by transgenera complementation, whereas the coccidian GAP45 homolog (designated here as) GAP70 specifically recruits the glideosome to the apical cap of the parasite

BCKDH: the missing link in apicomplexan mitochondrial metabolism is required for full virulence of Toxoplasma gondii and Plasmodium berghei

While the apicomplexan parasites Plasmodium falciparum and Toxoplasma gondii are thought to primarily depend on glycolysis for ATP synthesis, recent studies have shown that they can fully catabolize glucose in a canonical TCA cycle. However, these parasites lack a mitochondrial isoform of pyruvate dehydrogenase and the identity of the enzyme that catalyses the conversion of pyruvate to acetyl-CoA remains enigmatic. Here we demonstrate that the mitochondrial branched chain ketoacid dehydrogenase (BCKDH) complex is the missing link, functionally replacing mitochondrial PDH in both T. gondii and P. berghei. Deletion of the E1a subunit of T. gondii and P. berghei BCKDH significantly impacted on intracellular growth and virulence of both parasites. Interestingly, disruption of the P. berghei E1a restricted parasite development to reticulocytes only and completely prevented maturation of oocysts during mosquito transmission. Overall this study highlights the importance of the molecular adaptation of BCKDH in this important class of pathogens

Dissection of Besnoitia besnoiti intermediate host life cycle stages: From morphology to gene expression.

Cyst-forming Apicomplexa (CFA) of the Sarcocystidae have a ubiquitous presence as pathogens of humans and farm animals transmitted through the food chain between hosts with few notable exceptions. The defining hallmark of this family of obligate intracellular protists consists of their ability to remain for very long periods as infectious tissue cysts in chronically infected intermediate hosts. Nevertheless, each closely related species has evolved unique strategies to maintain distinct reservoirs on global scales and ensuring efficient transmission to definitive hosts as well as between intermediate hosts. Here, we present an in-depth comparative mRNA expression analysis of the tachyzoite and bradyzoite stages of Besnoitia besnoiti strain Lisbon14 isolated from an infected farm animal based on its annotated genome sequence. The B. besnoiti genome is highly syntenic with that of other CFA and also retains the capacity to encode a large majority of known and inferred factors essential for completing a sexual cycle in a yet unknown definitive host. This work introduces Besnoitia besnoiti as a new model for comparative biology of coccidian tissue cysts which can be readily obtained in high purity. This model provides a framework for addressing fundamental questions about the evolution of tissue cysts and the biology of this pharmacologically intractable infectious parasite stage

Dissection of Besnoitia besnoiti intermediate host life cycle stages: From morphology to gene expression

Cyst-forming Apicomplexa (CFA) of the Sarcocystidae have a ubiquitous presence as pathogens of humans and farm animals transmitted through the food chain between hosts with few notable exceptions. The defining hallmark of this family of obligate intracellular protists consists of their ability to remain for very long periods as infectious tissue cysts in chronically infected intermediate hosts. Nevertheless, each closely related species has evolved unique strategies to maintain distinct reservoirs on global scales and ensuring efficient transmission to definitive hosts as well as between intermediate hosts. Here, we present an in-depth comparative mRNA expression analysis of the tachyzoite and bradyzoite stages of Besnoitia besnoiti strain Lisbon14 isolated from an infected farm animal based on its annotated genome sequence. The B. besnoiti genome is highly syntenic with that of other CFA and also retains the capacity to encode a large majority of known and inferred factors essential for completing a sexual cycle in a yet unknown definitive host. This work introduces Besnoitia besnoiti as a new model for comparative biology of coccidian tissue cysts which can be readily obtained in high purity. This model provides a framework for addressing fundamental questions about the evolution of tissue cysts and the biology of this pharmacologically intractable infectious parasite stage

Cytokinetic abscission in Toxoplasma gondii is governed by protein phosphatase 2A and the daughter cell scaffold complex.

Cytokinetic abscission marks the final stage of cell division, during which the daughter cells physically separate through the generation of new barriers, such as the plasma membrane or cell wall. While the contractile ring plays a central role during cytokinesis in bacteria, fungi and animal cells, the process diverges in Apicomplexa. In Toxoplasma gondii, two daughter cells are formed within the mother cell by endodyogeny. The mechanism by which the progeny cells acquire their plasma membrane during the disassembly of the mother cell, allowing daughter cells to emerge, remains unknown. Here we identify and characterize five T. gondii proteins, including three protein phosphatase 2A subunits, which exhibit a distinct and dynamic localization pattern during parasite division. Individual downregulation of these proteins prevents the accumulation of plasma membrane at the division plane, preventing the completion of cellular abscission. Remarkably, the absence of cytokinetic abscission does not hinder the completion of subsequent division cycles. The resulting progeny are able to egress from the infected cells but fail to glide and invade, except in cases of conjoined twin parasites

Analysis and Design of CMOS Radio-Frequency Power Amplifiers

The continuous advancement of semiconductor technologies, especially CMOS technology, has enabled exponential growth of the wireless communication industry. This explosive growth in turn has completely changed people’s lives. The CMOS feature size scale down greatly benefits digital logic integrations, which result in more powerful, versatile, and economical digital signal processing. Further research and development has pushed analog, mixed-signal, and even radio-frequency (RF) circuit blocks to be implemented and integrated in CMOS. Future generations of wireless communication call for even further level of integration, and as of now, the only circuit block that is rarely integrated in CMOS along with other parts of the system is the power amplifier (PA). Due to the fact that the PA in a wireless communication system is the most power-hungry circuit block, the integration of RF PA in CMOS would potentially not only save the cost of the wireless communication system real estate, but also reduce power consumption since die-to-die connection loss can be eliminated. RF PA design involves handling large amounts of voltage and current at the radio frequencies, which in the present wireless communication standards are in the range of giga-hertz. Therefore, a good understanding of many aspects related to RF PA design is necessary. Theoretical analysis of the communication system, nonlinear effects of the PA, as well as the impedance matching network is systematically presented. The analysis of the nonlinear effects proposes a formal mathematical description of the multitone nonlinearity, and through its relationship with two-tone test, the proposed PA design methodology would greatly reduce the design time while improving the design accuracy. A thorough analysis of the available architecture and design techniques for efficiency and linearity enhancement of RF PA shows that despite tremendous amounts of research and development into this topic, the fundamental tradeoff between the two still limits the RF PA implementation largely within SiGe, GaAs, and InP technologies. A RF PA for Wideband Code-Division Multiple Access (WCDMA) application standard is proposed, designed, and implemented in CMOS that demonstrates the proposed segmentation technique that resolved the main tradeoff between power efficiency and linearity. The innovative architecture developed in this work is not limited to applications in the WCDMA communication protocol or the CMOS technology, although CMOS implementation would take advantage of the readily available digital resources

Erinnerung an W. Thielmann und Willingshausen

While the apicomplexan parasites Plasmodium falciparum and Toxoplasma gondii are thought to primarily depend on glycolysis for ATP synthesis, recent studies have shown that they can fully catabolize glucose in a canonical TCA cycle. However, these parasites lack a mitochondrial isoform of pyruvate dehydrogenase and the identity of the enzyme that catalyses the conversion of pyruvate to acetyl-CoA remains enigmatic. Here we demonstrate that the mitochondrial branched chain ketoacid dehydrogenase (BCKDH) complex is the missing link, functionally replacing mitochondrial PDH in both T. gondii and P. berghei. Deletion of the E1a subunit of T. gondii and P. berghei BCKDH significantly impacted on intracellular growth and virulence of both parasites. Interestingly, disruption of the P. berghei E1a restricted parasite development to reticulocytes only and completely prevented maturation of oocysts during mosquito transmission. Overall this study highlights the importance of the molecular adaptation of BCKDH in this important class of pathogens

The lectin-specific activity of Toxoplasma gondii microneme proteins 1 and 4 binds Toll-like receptor 2 and 4 N-glycans to regulate innate immune priming.

Infection of host cells by Toxoplasma gondii is an active process, which is regulated by secretion of microneme (MICs) and rhoptry proteins (ROPs and RONs) from specialized organelles in the apical pole of the parasite. MIC1, MIC4 and MIC6 assemble into an adhesin complex secreted on the parasite surface that functions to promote infection competency. MIC1 and MIC4 are known to bind terminal sialic acid residues and galactose residues, respectively and to induce IL-12 production from splenocytes. Here we show that rMIC1- and rMIC4-stimulated dendritic cells and macrophages produce proinflammatory cytokines, and they do so by engaging TLR2 and TLR4. This process depends on sugar recognition, since point mutations in the carbohydrate-recognition domains (CRD) of rMIC1 and rMIC4 inhibit innate immune cells activation. HEK cells transfected with TLR2 glycomutants were selectively unresponsive to MICs. Following in vitro infection, parasites lacking MIC1 or MIC4, as well as expressing MIC proteins with point mutations in their CRD, failed to induce wild-type (WT) levels of IL-12 secretion by innate immune cells. However, only MIC1 was shown to impact systemic levels of IL-12 and IFN-γ in vivo. Together, our data show that MIC1 and MIC4 interact physically with TLR2 and TLR4 N-glycans to trigger IL-12 responses, and MIC1 is playing a significant role in vivo by altering T. gondii infection competency and murine pathogenesis