The kinesin of the flagellum attachment zone in Leishmania is required for cell morphogenesis, cell division and virulence in the mammalian host.

Leishmania parasites possess a unique and complex cytoskeletal structure termed flagellum attachment zone (FAZ) connecting the base of the flagellum to one side of the flagellar pocket (FP), an invagination of the cell body membrane and the sole site for endocytosis and exocytosis. This structure is involved in FP architecture and cell morphogenesis, but its precise role and molecular composition remain enigmatic. Here, we characterized Leishmania FAZ7, the only known FAZ protein containing a kinesin motor domain, and part of a clade of trypanosomatid-specific kinesins with unknown functions. The two paralogs of FAZ7, FAZ7A and FAZ7B, display different localizations and functions. FAZ7A localizes at the basal body, while FAZ7B localizes at the distal part of the FP, where the FAZ structure is present in Leishmania. While null mutants of FAZ7A displayed normal growth rates, the deletion of FAZ7B impaired cell growth in both promastigotes and amastigotes of Leishmania. The kinesin activity is crucial for its function. Deletion of FAZ7B resulted in altered cell division, cell morphogenesis (including flagellum length), and FP structure and function. Furthermore, knocking out FAZ7B induced a mis-localization of two of the FAZ proteins, and disrupted the molecular organization of the FP collar, affecting the localization of its components. Loss of the kinesin FAZ7B has important consequences in the insect vector and mammalian host by reducing proliferation in the sand fly and pathogenicity in mice. Our findings reveal the pivotal role of the only FAZ kinesin as part of the factors important for a successful life cycle of Leishmania.

Efficient invasion by Toxoplasma depends on the subversion of host protein networks.

Apicomplexan parasites are important pathogens of humans and domestic animals, including Plasmodium species (the agents of malaria) and Toxoplasma gondii, which is responsible for toxoplasmosis. They replicate within the cells of their animal hosts, to which they gain access using a unique parasite-driven invasion process. At the core of the invasion machine is a structure at the interface between the invading parasite and host cell called the moving junction (MJ) 1 . The MJ serves as both a molecular doorway to the host cell and an anchor point enabling the parasite to engage its motility machinery to drive the penetration of the host cell 2 , ultimately yielding a protective vacuole 3 . The MJ is established through self-assembly of parasite proteins at the parasite-host interface 4 . However, it is unknown whether host proteins are subverted for MJ formation. Here, we show that Toxoplasma parasite rhoptry neck proteins (RON2, RON4 and RON5) cooperate to actively recruit the host CIN85, CD2AP and the ESCRT-I components ALIX and TSG101 to the MJ during invasion. We map the interactions in detail and demonstrate that the parasite mimics and subverts conserved binding interfaces with remarkable specificity. Parasite mutants unable to recruit these host proteins show inefficient host cell invasion in culture and attenuated virulence in mice. This study reveals molecular mechanisms by which parasites subvert widely conserved host machinery to force highly efficient host cell access.

Synthesis, antitubercular activity and mechanism of resistance of highly effective thiacetazone analogues.

Defining the pharmacological target(s) of currently used drugs and developing new analogues with greater potency are both important aspects of the search for agents that are effective against drug-sensitive and drug-resistant Mycobacterium tuberculosis. Thiacetazone (TAC) is an anti-tubercular drug that was formerly used in conjunction with isoniazid, but removed from the antitubercular chemotherapeutic arsenal due to toxic side effects. However, several recent studies have linked the mechanisms of action of TAC to mycolic acid metabolism and TAC-derived analogues have shown increased potency against M. tuberculosis. To obtain new insights into the molecular mechanisms of TAC resistance, we isolated and analyzed 10 mutants of M. tuberculosis that were highly resistant to TAC. One strain was found to be mutated in the methyltransferase MmaA4 at Gly101, consistent with its lack of oxygenated mycolic acids. All remaining strains harbored missense mutations in either HadA (at Cys61) or HadC (at Val85, Lys157 or Thr123), which are components of the ß-hydroxyacyl-ACP dehydratase complex that participates in the mycolic acid elongation step. Separately, a library of 31 new TAC analogues was synthesized and evaluated against M. tuberculosis. Two of these compounds, 15 and 16, exhibited minimal inhibitory concentrations 10-fold lower than the parental molecule, and inhibited mycolic acid biosynthesis in a dose-dependent manner. Moreover, overexpression of HadAB HadBC or HadABC in M. tuberculosis led to high level resistance to these compounds, demonstrating that their mode of action is similar to that of TAC. In summary, this study uncovered new mutations associated with TAC resistance and also demonstrated that simple structural optimization of the TAC scaffold was possible and may lead to a new generation of TAC-derived drug candidates for the potential treatment of tuberculosis as mycolic acid inhibitors.

Mycobacterium tuberculosis S-adenosyl-l-homocysteine hydrolase is negatively regulated by Ser/Thr phosphorylation.

S-Adenosylhomocysteine hydrolase (SahH) is known as an ubiquitous player in methylation-based process that maintains the intracellular S-adenosylhomocysteine (SAH) and S-adenosylmethionine (SAM) equilibrium. Given its crucial role in central metabolism in both eukaryotes and prokaryotes, it is assumed that SahH must be regulated, albeit little is known regarding molecular mechanisms governing its activity. We report here that SahH from Mycobacterium tuberculosis can be phosphorylated by mycobacterial Ser/Thr protein kinases and that phosphorylation negatively affects its enzymatic activity. Mass spectrometric analyses and site-directed mutagenesis identified Thr2 and Thr221 as the two phosphoacceptors. SahH_T2D, SahH_T221D and SahH_T2D/T221D, designed to mimic constitutive phosphorylation, exhibited markedly decreased activity compared to the wild-type enzyme. Both residues are fully conserved in other mycobacterial SahH orthologues, suggesting that SahH phosphorylation on Thr2 and Thr221 may represent a novel and presumably more general mechanism of regulation of the SAH/SAM balance in mycobacteria.

Phosphorylation of mycobacterial PcaA inhibits mycolic acid cyclopropanation: consequences for intracellular survival and for phagosome maturation block.

Pathogenic mycobacteria survive within macrophages by residing in phagosomes, which they prevent from maturing and fusing with lysosomes. Although several bacterial components were seen to modulate phagosome processing, the molecular regulatory mechanisms taking part in this process remain elusive. We investigated whether the phagosome maturation block (PMB) could be modulated by signaling through Ser/Thr phosphorylation. Here, we demonstrated that mycolic acid cyclopropane synthase PcaA, but not MmaA2, was phosphorylated by mycobacterial Ser/Thr kinases at Thr-168 and Thr-183 both in vitro and in mycobacteria. Phosphorylation of PcaA was associated with a significant decrease in the methyltransferase activity, in agreement with the strategic structural localization of these two phosphoacceptors. Using a BCG ΔpcaA mutant, we showed that PcaA was required for intracellular survival and prevention of phagosome maturation in human monocyte-derived macrophages. The physiological relevance of PcaA phosphorylation was further assessed by generating PcaA phosphoablative (T168A/T183A) or phosphomimetic (T168D/T183D) mutants. In contrast to the wild-type and phosphoablative pcaA alleles, introduction of the phosphomimetic pcaA allele in the ΔpcaA mutant failed to restore the parental mycolic acid profile and cording morphotype. Importantly, the PcaA phosphomimetic strain, as the ΔpcaA mutant, exhibited reduced survival in human macrophages and was unable to prevent phagosome maturation. Our results add new insight into the importance of mycolic acid cyclopropane rings in the PMB and provide the first evidence of a Ser/Thr kinase-dependent mechanism for modulating mycolic acid composition and PMB.

Deciphering the Leishmania exoproteome: what we know and what we can learn.

Parasitic protozoa of the genus Leishmania are the causative agents of leishmaniasis. Survival and transmission of these parasites in their different hosts require membrane-bound or extracellular factors to interact with and modify their host environments. Over the last decade, several approaches have been applied to study all the extracellular proteins exported by an organism at a particular time or stage in its life cycle and under defined conditions, collectively termed the secretome or the exoproteome. In this review, we focus on emerging data shedding light on the secretion mechanisms involved in the production of the Leishmania exoproteome. We also describe other methodologies currently available that could be used to analyse the Leishmania exoproteome. Understanding the complexity of the Leishmania exoproteome is a key component to elucidating the mechanisms used by these parasites for exporting proteins to the extracellular space during its life cycle. Given the importance of extracellular factors, a detailed knowledge of the Leishmania exoproteome may provide novel targets for rational drug design and/or a source of antigens for vaccine development.

Chagas disease in rural areas of Chaco Province, Argentina: epidemiologic survey in humans, reservoirs, and vectors.

We studied the seroprevalence of antibodies against Trypanosoma cruzi in the human population along with domiciliary infestation by triatomine bugs in an area endemic for Chagas disease in the Chaco Province of Argentina. In addition, we carried out parasitologic surveys in patients, dogs, wild mammals, and vectors. The mean seroprevalence in humans was 27.81% (109 of 392) and 24.14% (63 of 261) in 1-15-year-old children. The minimum domiciliary infestation rate was 13.33%, with certain areas reaching 53.85%. The prevalence was 15.09% (16 of 106) in dogs and 35.71% (10 of 28) in opossums. Infection with T. cruzi was detected in 30.10% (59 of 196) of the Triatoma infestans tested. Compared with nationwide studies, our data suggest that 1) there are zones requiring immediate sanitary action, and 2) nationwide estimates are based on very heterogeneous epidemiologic situations. This heterogeneity emphasizes the importance of in-depth studies of restricted areas to provide additional information for a better understanding of the present status of Chagas disease in Argentina.