Many members of the phylum of Apicomplexa have adopted an obligate intracellular life style and critically depend on active invasion and egress from the infected cells to complete their lytic cycle. Toxoplasma gondii belongs to the coccidian subgroup of the Apicomplexa, and as such, the invasive tachyzoite contains an organelle termed the conoid at its extreme apex. This motile organelle consists of a unique polymer of tubulin fibres and protrudes in both gliding and invading parasites. The class XIV myosin A, which is conserved across the Apicomplexa phylum, is known to critically contribute to motility, invasion and egress from infected cells. The MyoA-glideosome is anchored to the inner membrane complex (IMC) and is assumed to translocate the components of the circular junction secreted by the micronemes and rhoptries, to the rear of the parasite. Here we comprehensively characterise the class XIV myosin H (MyoH) and its associated light chains. We show that the 3 alpha-tubulin suppressor domains, located in MyoH tail, are necessary to anchor this motor to the conoid. Despite the presence of an intact MyoA-glideosome, conditional disruption of TgMyoH severely compromises parasite motility, invasion and egress from infected cells. We demonstrate that MyoH is necessary for the translocation of the circular junction from the tip of the parasite, where secretory organelles exocytosis occurs, to the apical position where the IMC starts. This study attributes for the first time a direct function of the conoid in motility and invasion, and establishes the indispensable role of MyoH in initiating the first step of motility along this unique organelle, which is subsequently relayed by MyoA to enact effective gliding and invasion.

Coronins are involved in the regulation of actin dynamics in a multifaceted way, participating in cell migration and vesicular trafficking. Apicomplexan parasites, which exhibit an actin-dependent gliding motility that is essential for traversal through tissues, as well as invasion of and egress from host cells, express only a single coronin, whereas higher eukaryotes possess several isoforms. We set out to characterize the 3-D structure, biochemical function, subcellular localization, and genetic ablation of Toxoplasma gondii coronin (TgCOR), to shed light on its biological role. A combination of X-ray crystallography, small-angle scattering of X-rays, and light scattering revealed the atomic structure of the conserved WD40 domain and the dimeric arrangement of the fulllength protein. TgCOR binds to F-actin and increases the rate and extent of actin polymerization. In vivo, TgCOR relocalizes transiently to the posterior pole of motile and invading parasites, independent of actin dynamics, but concomitant to microneme secretory organelle discharge. TgCOR contributes to, but is not essential for, invasion and egress. Taken together, our data point toward a role for TgCOR in stabilizing newly formed, short filaments and F-actin cross-linking, as well as functions linked to endocytosis and recycling of membranes.-Salamun, J., Kallio, J. P., Daher, W., Soldati-Favre, D., Kursula, I. Structure of Toxoplasma gondii coronin, an actin-binding protein that relocalizes to the posterior pole of invasive parasites and contributes to invasion and egress. FASEB J. 28, 4729 -4747 (2014). www.fasebj.orgKey Words: apicomplexan parasite ⅐ gliding motility ⅐ WD40 domain TOXOPLASMA GONDII is an obligate intracellular parasite of medical and veterinary significance that invades almost any nucleated cell from virtually all warmblooded animals. The invasive stages exhibit a substrate-dependent motility, driven by an actin-and myosin-based motor complex machinery termed the glideosome, which is critical for parasite dissemination (1). Gliding motility depends on an intact parasite actin cytoskeleton and requires actin polymerization (2). However, parasite actin filaments have been difficult to visualize in physiological conditions. Typically, apicomplexan actins appear to be maintained mainly in globular form (3). In vitro polymerization assays performed on purified T. gondii actin indicated that the actin filaments are very short (50 -100 nm; ref. 4). The instability of apicomplexan actin filaments seems to be a prerequisite for efficient gliding motility, since stabilization of actin filaments, either by the known stabilizing agent jasplakinolide (JAS; refs. 2, 5, 6) or by substituting key residues assumed to be involved in the intermolecular contacts between different protomers, disrupt the normal gliding motility of parasites (7).Actin dynamics and its regulation in the Apicomplexa differ significantly from higher eukaryotes. The rapid 1 These authors contributed equally to this work.

Several SARS-CoV-2 variants of concern (VOC) are spreading rapidly in different regions of the world. The underlying mechanisms behind their transmission advantage remain unclear. We measured viral load in 950 individuals and found that infections with variant Alpha exhibit a higher viral load and longer viral shedding compared to non-VOC. We then used a transmission model to analyze the spread of variant Alpha in Geneva, Switzerland, and variant Beta in South Africa. We estimated that Alpha is either associated with a 37% (95% compatibility interval, CI: 25-63%) increase in transmissibility or a 51% (95% CI: 32-80%) increase of the infectious duration, or a combination of the two mechanisms. Assuming 50% immune evasion for Beta, we estimated a 23% (95% CI: 10-37%) increase in transmissibility or a 38% (95% CI: 15-78%) increase of the infectious duration for this variant. Beta is expected to outgrow Alpha in regions where the level of naturally acquired immunity from previously circulating variants exceeds 20% to 40%. Close monitoring of Alpha and Beta in regions with different levels of immunity will help to anticipate the global spread of these and future variants.

Background Persistent symptoms of SARS‐CoV‐2 are prevalent weeks to months following the infection. To date, it is difficult to disentangle the direct from the indirect effects of SARS‐CoV‐2, including lockdown, social, and economic factors. Objective The study aims to characterize the prevalence of symptoms, functional capacity, and quality of life at 12 months in outpatient symptomatic individuals tested positive for SARS‐CoV‐2 compared to individuals tested negative. Methods From 23 April to 27 July 2021, outpatient symptomatic individuals tested for SARS‐CoV‐2 at the Geneva University Hospitals were followed up 12 months after their test date. Results At 12 months, out of the 1447 participants (mean age 45.2 years, 61.2% women), 33.4% reported residual mild to moderate symptoms following SARS‐CoV‐2 infection compared to 6.5% in the control group. Symptoms included fatigue (16% vs. 3.1%), dyspnea (8.9% vs. 1.1%), headache (9.8% vs. 1.7%), insomnia (8.9% vs. 2.7%), and difficulty concentrating (7.4% vs. 2.5%). When compared to the control group, 30.5% of SARS‐CoV‐2 positive individuals reported functional impairment at 12 months versus 6.6%. SARS‐CoV‐2 infection was associated with the persistence of symptoms (adjusted odds ratio [aOR] 4.1; 2.60–6.83) and functional impairment (aOR 3.54; 2.16–5.80) overall, and in subgroups of women, men, individuals younger than 40 years, those between 40–59 years, and in individuals with no past medical or psychiatric history. Conclusion SARS‐CoV‐2 infection leads to persistent symptoms over several months, including in young healthy individuals, in addition to the pandemic effects, and potentially more than other common respiratory infections. Symptoms impact functional capacity up to 12 months post infection.

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