Structural Changes of the Paraflagellar Rod during Flagellar Beating in Trypanosoma cruzi

, the agent of Chagas disease, is a protozoan member of the Kinetoplastidae family characterized for the presence of specific and unique structures that are involved in different cell activities. One of them is the paraflagellar rod (PFR), a complex array of filaments connected to the flagellar axoneme. Although the function played by the PFR is not well established, it has been shown that silencing of the synthesis of its major proteins by either knockout of RNAi impairs and/or modifies the flagellar motility.Here, we present results obtained by atomic force microscopy (AFM) and transmission electron microscopy (TEM) of replicas of quick-frozen, freeze-fractured, deep-etched and rotary-replicated cells to obtain detailed information of the PFR structures in regions of the flagellum in straight and in bent state. The images obtained show that the PFR is not a fixed and static structure. The pattern of organization of the PFR filament network differs between regions of the flagellum in a straight state and those in a bent state. Measurements of the distances between the PFR filaments and the filaments that connect the PFR to the axoneme as well as of the angles between the intercrossed filaments supported this idea.Graphic computation based on the information obtained allowed the proposal of an animated model for the PFR structure during flagellar beating and provided a new way of observing PFR filaments during flagellar beating

Comparative radiological features of disseminated disease due to Mycobacterium tuberculosis vs non-tuberculosis mycobacteria among AIDS patients in Brazil

Background: Disseminated mycobacterial disease is an important cause of morbidity and mortality in patients with HIV-infection. Nonspecific clinical presentation makes the diagnosis difficult and sometimes neglected. Methods: We conducted a retrospective cohort study to compare the presentation of disseminated Mycobacterial tuberculosis (MTB) and non-tuberculous Mycobacterial (NTM) disease in HIV-positive patients from 1996 to 2006 in Brazil. Results: Tuberculosis (TB) was diagnosed in 65 patients (67.7%) and NTM in 31 (32.3%) patients. Patients with NTM had lower CD4 T cells counts (median 13.0 cells/mm3 versus 42.0 cells/mm3, P = 0.002). Patients with tuberculosis had significantly more positive acid-fast smears (48.0% vs 13.6%, P = 0.01). On chest X-ray, miliary infiltrate was only seen in patients with MTB (28.1% vs. 0.0%, P = 0.01). Pleural effusion was more common in patients with MTB (45.6% vs. 13.0%, P = 0.01). Abdominal adenopathy (73.1% vs. 33.3%, P = 0.003) and splenic hypoechoic nodules (38.5% vs. 0.0%, P = 0.002) were more common in patients with TB. Conclusion: Miliary pulmonary pattern on X-ray, pleural effusion, abdominal adenopathy, and splenic hypoechoic nodules were imaging findings associated with the diagnosis of tuberculosis in HIV-infected patients. Recognition of these imaging features will help to distinguish TB from NTM in AIDS patients with fever of unknown origin due to disseminated mycobacterial disease

Modulation of the surface proteome through multiple ubiquitylation pathways in African Trypanosomes

Recently we identified multiple suramin-sensitivity genes with a genome wide screen in Trypanosoma brucei that includes the invariant surface glycoprotein ISG75, the adaptin-1 (AP-1) complex and two deubiquitylating enzymes (DUBs) orthologous to ScUbp15/HsHAUSP1 and pVHL-interacting DUB1 (type I), designated TbUsp7 and TbVdu1, respectively. Here we have examined the roles of these genes in trafficking of ISG75, which appears key to suramin uptake. We found that, while AP-1 does not influence ISG75 abundance, knockdown of TbUsp7 or TbVdu1 leads to reduced ISG75 abundance. Silencing TbVdu1 also reduced ISG65 abundance. TbVdu1 is a component of an evolutionarily conserved ubiquitylation switch and responsible for rapid receptor modulation, suggesting similar regulation of ISGs in T. brucei. Unexpectedly, TbUsp7 knockdown also blocked endocytosis. To integrate these observations we analysed the impact of TbUsp7 and TbVdu1 knockdown on the global proteome using SILAC. For TbVdu1, ISG65 and ISG75 are the only significantly modulated proteins, but for TbUsp7 a cohort of integral membrane proteins, including the acid phosphatase MBAP1, that is required for endocytosis, and additional ISG-related proteins are down-regulated. Furthermore, we find increased expression of the ESAG6/7 transferrin receptor and ESAG5, likely resulting from decreased endocytic activity. Therefore, multiple ubiquitylation pathways, with a complex interplay with trafficking pathways, control surface proteome expression in trypanosomes

How Does the VSG Coat of Bloodstream Form African Trypanosomes Interact with External Proteins?

Variations on the statement "the variant surface glycoprotein (VSG) coat that covers the external face of the mammalian bloodstream form of Trypanosoma brucei acts a physical barrier" appear regularly in research articles and reviews. The concept of the impenetrable VSG coat is an attractive one, as it provides a clear model for understanding how a trypanosome population persists; each successive VSG protects the plasma membrane and is immunologically distinct from previous VSGs. What is the evidence that the VSG coat is an impenetrable barrier, and how do antibodies and other extracellular proteins interact with it? In this review, the nature of the extracellular surface of the bloodstream form trypanosome is described, and past experiments that investigated binding of antibodies and lectins to trypanosomes are analysed using knowledge of VSG sequence and structure that was unavailable when the experiments were performed. Epitopes for some VSG monoclonal antibodies are mapped as far as possible from previous experimental data, onto models of VSG structures. The binding of lectins to some, but not to other, VSGs is revisited with more recent knowledge of the location and nature of N-linked oligosaccharides. The conclusions are: (i) Much of the variation observed in earlier experiments can be explained by the identity of the individual VSGs. (ii) Much of an individual VSG is accessible to antibodies, and the barrier that prevents access to the cell surface is probably at the base of the VSG N-terminal domain, approximately 5 nm from the plasma membrane. This second conclusion highlights a gap in our understanding of how the VSG coat works, as several plasma membrane proteins with large extracellular domains are very unlikely to be hidden from host antibodies by VSG.The authors’ lab is funded by the Wellcome Trust (093008/Z10/Z) and the Medical Research Council (MR/L008246/1). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.This is the final version of the article. It was first available from PLOS via http://dx.doi.org/10.1371/journal.ppat.100525

Envenomation by Micrurus coral snakes in the Brazilian Amazon region: report of two cases

Two cases of proven coral snake bites were reported in Belém, Pará State, Brazil. The first case was a severe one caused by Micrurus surinamensis. The patient required mechanical ventilation due to acute respiratory failure. The second case showed just mild signs of envenomation caused by Micrurus filiformis. Both patients received specific Micrurus antivenom and were discharged without further complications. Coral snake bites are scarcely reported in the Amazon region and there is a broad spectrum of clinical manifestations, varying from extremely mild to those which may rapidly lead to death if the patient is not treated as soon as possible