Actin-depolymerizing factor, ADF/cofilin, is essentially required in assembly of Leishmania flagellum

Recombinant actin-depolymerizing factor of the apicomplexan Neospora caninum (NcADF) is susceptible to oxidation

Neospora caninum is a member of Apicomplexa Phylum and the causative agent of neosporosis, a disease responsible for abortions in cattle. Apicomplexan parasites have a limited set of actin-binding proteins conducting the regulation of the dynamics of nonconventional actin. The parasite actin-based motility is implicated in the parasite invasion process in the host cell. Once no commercial strategy for the neosporosis control is available, the interference in the parasite actin function may result in novel drug targets. Actin-depolymerization factor (ADF) is a member of the ADF/cofilin family, primarily known for its function in actin severing and depolymerization. ADF/cofilins are versatile proteins modulated by different mechanisms, including reduction and oxidation. In apicomplexan parasites, the mechanisms involved in the modulation of ADF function are barely explored and the effects of oxidation in the protein are unknown so far. In this study, we used the oxidants N-chlorotaurine (NCT) and H₂O₂ to investigate the susceptibility of the recombinant N. caninum ADF (NcADF) to oxidation. After exposing the protein to either NCT or H₂O₂, the dimerization status and cysteine residue oxidation were determined. Also, the interference of NcADF oxidation in the interaction with actin was assessed. The treatment of the recombinant protein with oxidants reversibly induced the production of dimers, indicating that disulfide bonds between NcADF cysteine residues were formed. In addition, the exposure of NcADF to NCT resulted in more efficient oxidation of the cysteine residues compared to H₂O₂. Finally, the oxidation of NcADF by NCT reduced the ability of actin-binding and altered the function of NcADF in actin polymerization. Altogether, our results clearly show that recombinant NcADF is sensitive to redox conditions, indicating that the function of this protein in cellular processes involving actin dynamics may be modulated by oxidation.

Structural basis of rapid actin dynamics in the evolutionarily divergent Leishmania parasite

Actin polymerization generates forces for cellular processes throughout the eukaryotic kingdom, but our understanding of the 'ancient' actin turnover machineries is limited. We show that, despite > 1 billion years of evolution, pathogenic Leishmania major parasite and mammalian actins share the same overall fold and co-polymerize with each other. Interestingly, Leishmania harbors a simple actin-regulatory machinery that lacks cofilin 'cofactors', which accelerate filament disassembly in higher eukaryotes. By applying single-filament biochemistry we discovered that, compared to mammalian proteins, Leishmania actin filaments depolymerize more rapidly from both ends, and are severed > 100-fold more efficiently by cofilin. Our high-resolution cryo-EM structures of Leishmania ADP-, ADP-Pi- and cofilin-actin filaments identify specific features at actin subunit interfaces and cofilin-actin interactions that explain the unusually rapid dynamics of parasite actin filaments. Our findings reveal how divergent parasites achieve rapid actin dynamics using a remarkably simple set of actin-binding proteins, and elucidate evolution of the actin cytoskeleton.

Emerging Functions of Actins and Actin Binding Proteins in Trypanosomatids

Actin is the major protein constituent of the cytoskeleton that performs wide range of cellular functions. It exists in monomeric and filamentous forms, dynamics of which is regulated by a large repertoire of actin binding proteins. However, not much was known about existence of these proteins in trypanosomatids, till the genome sequence data of three important organisms of this class, viz. Trypanosoma brucei, Trypanosoma cruzi and Leishmania major, became available. Here, we have reviewed most of the findings reported to date on the intracellular distribution, structure and functions of these proteins and based on them, we have hypothesized some of their functions. The major findings are as follows: (1) All the three organisms encode at least a set of ten actin binding proteins (profilin, twinfilin, ADF/cofilin, CAP/srv2, CAPz, coronin, two myosins, two formins) and one isoform of actin, except that T. cruzi encodes for three formins and several myosins along with four actins. (2) Actin 1 and a few actin binding proteins (ADF/cofilin, profilin, twinfilin, coronin and myosin13 in L. donovani; ADF/cofilin, profilin and myosin1 in T. brucei; profilin and myosin-F in T.cruzi) have been identified and characterized. (3) In all the three organisms, actin cytoskeleton has been shown to regulate endocytosis and intracellular trafficking. (4) Leishmania actin1 has been the most characterized protein among trypanosomatid actins. (5) This protein is localized to the cytoplasm as well as in the flagellum, nucleus and kinetoplast, and in vitro, it binds to DNA and displays scDNA relaxing and kDNA nicking activities. (6) The pure protein prefers to form bundles instead of thin filaments, and does not bind DNase1 or phalloidin. (7) Myosin13, myosin1 and myosin-F regulate endocytosis and intracellular trafficking, respectively, in Leishmania, T. brucei and T. cruzi. (8) Actin-dependent myosin13 motor is involved in dynamics and assembly of Leishmania flagellum. (9) Leishmania twinfilin localizes mostly to the nucleolus and coordinates karyokinesis by effecting splindle elongation and DNA synthesis. (10) Leishmania coronin binds and promotes actin filament formation and exists in tetrameric form rather than trimeric form, like other coronins. (11) Trypanosomatid profilins are essential for survival of all the three parasites.

Deciphering the role of UBA-like domains in intraflagellar distribution and functions of myosin XXI in Leishmania

Myosin XXI (Myo21) is a novel class of myosin present in all kinetoplastid parasites, such as Trypanosoma and Leishmania. This protein in Leishmania promastigotes is predominantly localized to the proximal region of the flagellum, and is involved in the flagellum assembly, cell motility and intracellular vesicle transport. As Myo21 contains two ubiquitin associated (UBA)-like domains (UBLD) in its amino acid sequence, we considered it of interest to analyze the role of these domains in the intracellular distribution and functions of this protein in Leishmania cells. In this context, we created green fluorescent protein (GFP)-conjugates of Myo21 constructs lacking one of the two UBLDs at a time or both the UBLDs as well as GFP-conjugates of only the two UBLDs and Myo21 tail lacking the two UBLDs and separately expressed them in the Leishmania cells. Our results show that unlike Myo21-GFP, Myo21-GFP constructs lacking either one or both the UBLDs failed to concentrate and co-distribute with actin in the proximal region of the flagellum. Nevertheless, the GFP conjugate of only the two UBLDs was found to predominantly localize to the flagellum base. Additionally, the cells that expressed only one or both the UBLDs-deleted Myo21-GFP constructs possessed shorter flagellum and displayed slower motility, compared to Myo21-GFP expressing cells. Further, the intracellular vesicle transport and cell growth were severely impaired in the cells that expressed both the UBLDs deleted Myo21-GFP construct, but in contrast, virtually no effect was observed on the intracellular vesicle transport and growth in the cells that expressed single UBLD deleted mutant proteins. Moreover, the observed slower growth of both the UBLDs-deleted Myo21-GFP expressing cells was primarily due to delayed G2/M phase caused by aberrant nuclear and daughter cell segregation during their cell division process. These results taken together clearly reveal that the presence of UBLDs in Myo21 are essentially required for its predominant localization to the flagellum base, and perhaps also in its involvement in the flagellum assembly and cell division. Possible role of UBLDs in involvement of Myo21 during Leishmania flagellum assembly and cell cycle is discussed.

Shape, form, function and Leishmania pathogenicity: from textbook descriptions to biological understanding

The shape and form of protozoan parasites are inextricably linked to their pathogenicity. The evolutionary pressure associated with establishing and maintaining an infection and transmission to vector or host has shaped parasite morphology. However, there is not a 'one size fits all' morphological solution to these different pressures, and parasites exhibit a range of different morphologies, reflecting the diversity of their complex life cycles. In this review, we will focus on the shape and form of Leishmania spp., a group of very successful protozoan parasites that cause a range of diseases from self-healing cutaneous leishmaniasis to visceral leishmaniasis, which is fatal if left untreated.

Chlamydomonas FAP265 is a tubulin polymerization promoting protein, essential for flagellar reassembly and hatching of daughter cells from the sporangium

Tubulin polymerization promoting proteins (TPPPs) belong to a family of neomorphic moon lighting proteins, involved in various physiological and pathological conditions. In physiological conditions, TPPPs play an important role in microtubule dynamics regulating mitotic spindle assembly and in turn cell proliferation. In pathological situations, TPPPs interact with α-synuclein and β-amyloid and promote their aggregation leading to Parkinson’s disease and multiple system atrophy. Orthologs of TPPP family proteins were identified in ciliary proteomes from various organisms including Chlamydomonas but their role in ciliogenesis was not known. Here we showed that Flagellar Associated Protein, FAP265, a Chlamydomonas homologue of TPPP family proteins, localizes in the cytosol, at the basal bodies and in the flagella of vegetative Chlamydomonas cells. During cell division, the protein was found as a distinct spot in the nucleus and at the cleavage furrow which forms between the daughter cells. Further null mutants of Chlamydomonas FAP265 protein, fap265, showed severe defects in hatching from the mother sporangium. Daughter cells of fap265 were significantly larger in size compared with wild type cells. Moreover, the daughter cells present within the mother sporangium failed to form flagella before hatching. They reassembled their flagella only after hatching from the sporangium suggesting that FAP265 plays an important role in flagellar reassembly after cell division.

Solution structures and dynamics of ADF/cofilins UNC-60A and UNC-60B from Caenorhabditis elegans

The nematode Caenorhabditis elegans has two ADF (actin-depolymerizing factor)/cofilin isoforms, UNC-60A and UNC-60B, which are expressed by the unc60 gene by alternative splicing. UNC-60A has higher activity to cause net depolymerization, and to inhibit polymerization, than UNC-60B. UNC-60B, on the other hand, shows much stronger severing activity than UNC-60A. To understand the structural basis of their functional differences, we have determined the solution structures of UNC-60A and UNC-60B proteins and characterized their backbone dynamics. Both UNC-60A and UNC-60B show a conserved ADF/cofilin fold. The G-actin (globular actin)-binding regions of the two proteins are structurally and dynamically conserved. Accordingly, UNC-60A and UNC-60B individually bind to rabbit muscle ADP-G-actin with high affinities, with Kd values of 32.25 nM and 8.62 nM respectively. The primary differences between these strong and weak severing proteins were observed in the orientation and dynamics of the F-actin (filamentous actin)-binding loop (F-loop). In the strong severing activity isoform UNC-60B, the orientation of the F-loop was towards the recently identified F-loop-binding region on F-actin, and the F-loop was relatively more flexible with 14 residues showing motions on a nanosecond-picosecond timescale. In contrast, in the weak severing protein isoform UNC-60A, the orientation of the F-loop was away from the F-loop-binding region and inclined towards its own C-terminal and strand β6. It was also relatively less flexible with only five residues showing motions on a nanosecond-picosecond timescale. These differences in structure and dynamics seem to directly correlate with the differential F-actin site-binding and severing properties of UNC-60A and UNC-60B, and other related ADF/cofilin proteins.

The eukaryotic flagellum makes the day: novel and unforeseen roles uncovered after post-genomics and proteomics data

This review will summarize and discuss the current biological understanding of the motile eukaryotic flagellum, as posed out by recent advances enabled by post-genomics and proteomics approaches. The organelle, which is crucial for motility, survival, differentiation, reproduction, division and feeding, among other activities, of many eukaryotes, is a great example of a natural nanomachine assembled mostly by proteins (around 350-650 of them) that have been conserved throughout eukaryotic evolution. Flagellar proteins are discussed in terms of their arrangement on to the axoneme, the canonical “9+2” microtubule pattern, and also motor and sensorial elements that have been detected by recent proteomic analyses in organisms such as Chlamydomonas reinhardtii, sea urchin, and trypanosomatids. Such findings can be remarkably matched up to important discoveries in vertebrate and mammalian types as diverse as sperm cells, ciliated kidney epithelia, respiratory and oviductal cilia, and neuro-epithelia, among others. Here we will focus on some exciting work regarding eukaryotic flagellar proteins, particularly using the flagellar proteome of C. reinhardtii as a reference map for exploring motility in function, dysfunction and pathogenic flagellates. The reference map for the eukaryotic flagellar proteome consists of 652 proteins that include known structural and intraflagellar transport (IFT) proteins, less well-characterized signal transduction proteins and flagellar associated proteins (FAPs), besides almost two hundred unannotated conserved proteins, which lately have been the subject of intense investigation and of our present examination.

ATP-dependent regulation of actin monomer-filament equilibrium by cyclase-associated protein and ADF/cofilin

CAP (cyclase-associated protein) is a conserved regulator of actin filament dynamics. In the nematode Caenorhabditis elegans, CAS-1 is an isoform of CAP that is expressed in striated muscle and regulates sarcomeric actin assembly. In the present study, we report that CAS-2, a second CAP isoform in C. elegans, attenuates the actin-monomer-sequestering effect of ADF (actin depolymerizing factor)/cofilin to increase the steady-state levels of actin filaments in an ATP-dependent manner. CAS-2 binds to actin monomers without a strong preference for either ATP- or ADP-actin. CAS-2 strongly enhances the exchange of actin-bound nucleotides even in the presence of UNC-60A, a C. elegans ADF/cofilin that inhibits nucleotide exchange. UNC-60A induces the depolymerization of actin filaments and sequesters actin monomers, whereas CAS-2 reverses the monomer-sequestering effect of UNC-60A in the presence of ATP, but not in the presence of only ADP or the absence of ATP or ADP. A 1:100 molar ratio of CAS-2 to UNC-60A is sufficient to increase actin filaments. CAS-2 has two independent actin-binding sites in its N- and C-terminal halves, and the C-terminal half is necessary and sufficient for the observed activities of the full-length CAS-2. These results suggest that CAS-2 (CAP) and UNC-60A (ADF/cofilin) are important in the ATP-dependent regulation of the actin monomer-filament equilibrium.

Centrosomal protein CEP104 (Chlamydomonas FAP256) moves to the ciliary tip during ciliary assembly

The ciliary tip has been implicated in ciliary assembly and disassembly, and signaling, yet information on its protein composition is limited. Using comparative, quantitative proteomics based on the fact that tip proteins will be approximately twice as concentrated in half-length compared with full-length flagella, we have identified FAP256 as a tip protein in Chlamydomonas. FAP256 localizes to the tips of both central pair and outer doublet microtubules (MTs) and it remains at the tip during flagellar assembly and disassembly. Similarly, its vertebrate counterpart, CEP104, localizes on the distal ends of both centrioles of nondividing cells until the mother centriole forms a cilium and then localizes at the tip of the elongating cilium. A null mutant of FAP256 in Chlamydomonas and RNAi in vertebrate cells showed that FAP256/CEP104 is required for ciliogenesis in a high percentage of cells. In those cells that could form cilia, there were structural deformities at the ciliary tips.

ADF/cofilin is not essential but is critically important for actin activities during phagocytosis in Tetrahymena thermophila

ADF/cofilin is a highly conserved actin-modulating protein. Reorganization of the actin cytoskeleton in vivo through severing and depolymerizing of F-actin by this protein is essential for various cellular events, such as endocytosis, phagocytosis, cytokinesis, and cell migration. We show that in the ciliate Tetrahymena thermophila, the ADF/cofilin homologue Adf73p associates with actin on nascent food vacuoles. Overexpression of Adf73p disrupted the proper localization of actin and inhibited the formation of food vacuoles. In vitro, recombinant Adf73p promoted the depolymerization of filaments made of T. thermophila actin (Act1p). Knockout cells lacking the ADF73 gene are viable but grow extremely slowly and have a severely decreased rate of food vacuole formation. Knockout cells have abnormal aggregates of actin in the cytoplasm. Surprisingly, unlike the case in animals and yeasts, in Tetrahymena, ADF/cofilin is not required for cytokinesis. Thus, the Tetrahymena model shows promise for future studies of the role of ADF/cofilin in vivo.

Structural and functional insight into ADF/cofilin from Trypanosoma brucei

The ADF/cofilin family has been characterized as a group of actin-binding proteins critical for controlling the assembly of actin within the cells. In this study, the solution structure of the ADF/cofilin from Trypanosoma brucei (TbCof) was determined by NMR spectroscopy. TbCof adopts the conserved ADF/cofilin fold with a central β-sheet composed of six β-strands surrounded by five α-helices. Isothermal titration calorimetry experiments denoted a submicromolar affinity between TbCof and G-actin, and the affinity between TbCof and ADP-G-actin was five times higher than that between TbCof and ATP-G-actin at low ionic strength. The results obtained from electron microscopy and actin filament sedimentation assays showed that TbCof depolymerized but did not co-sediment with actin filaments and its ability of F-actin depolymerization was pH independent. Similar to actin, TbCof was distributed throughout the cytoplasm. All our data indicate a structurally and functionally conserved ADF/cofilin from Trypanosoma brucei.

A member of the Ras oncogene family, RAP1A, mediates antileishmanial activity of monastrol

Objectives

To investigate the mode of action of monastrol in intracellular Leishmania.

Methods

Microarray experiments were conducted on an Affymetrix GeneChip^® Human Genome U133 Plus 2.0 Array, to determine the genes that encode proteins related to pathological alterations of cell signalling pathways in intracellular Leishmania amastigotes in response to monastrol treatment.

Results

Monastrol induced unprenylated Rap1A in intracellular Leishmania when exposed to this anticancer drug at the IC₅₀ (10 μM). Monastrol, known to cause mitotic arrest in cancer cells, inhibited Rap1A prenylation (geranylgeranylation) in intracellular Leishmania, which resulted in blockade at the G1 phase of the cell cycle. Growth inhibition, rather than apoptosis, was found to be the mechanism by which monastrol displays antileishmanial activity.

Conclusions

Prenylation inhibitors (unprenylation) of cell signalling pathways can be exploited in Leishmania parasites as novel therapeutic tools.

Overexpression of S4D mutant of Leishmania donovani ADF/cofilin impairs flagellum assembly by affecting actin dynamics

Leishmania, like other eukaryotes, contains large amounts of actin and a number of actin-related and actin binding proteins. Our earlier studies have shown that deletion of the gene corresponding to Leishmania actin-depolymerizing protein (ADF/cofilin) adversely affects flagellum assembly, intracellular trafficking, and cell division. To further analyze this, we have now created ADF/cofilin site-specific point mutants and then examined (i) the actin-depolymerizing, G-actin binding, and actin-bound nucleotide exchange activities of the mutant proteins and (ii) the effect of overexpression of these proteins in wild-type cells. Here we show that S4D mutant protein failed to depolymerize F-actin but weakly bound G-actin and inhibited the exchange of G-actin-bound nucleotide. We further observed that overexpression of this protein impaired flagellum assembly and consequently cell motility by severely impairing the assembly of the paraflagellar rod, without significantly affecting vesicular trafficking or cell growth. Taken together, these results indicate that dynamic actin is essentially required in assembly of the eukaryotic flagellum.

Solution structure and dynamics of ADF from Toxoplasma gondii

Toxoplasma gondii ADF (TgADF) belongs to a functional subtype characterized by strong G-actin sequestering activity and low F-actin severing activity. Among the characterized ADF/cofilin proteins, TgADF has the shortest length and is missing a C-terminal helix implicated in F-actin binding. In order to understand its characteristic properties, we have determined the solution structure of TgADF and studied its backbone dynamics from ¹⁵N-relaxation measurements. TgADF has conserved ADF/cofilin fold consisting of a central mixed β-sheet comprised of six β-strands that are partially surrounded by three α-helices and a C-terminal helical turn. The high G-actin sequestering activity of TgADF relies on highly structurally and dynamically optimized interactions between G-actin and G-actin binding surface of TgADF. The equilibrium dissociation constant for TgADF and rabbit muscle G-actin was 23.81 nM, as measured by ITC, which reflects very strong affinity of TgADF and G-actin interactions. The F-actin binding site of TgADF is partially formed, with a shortened F-loop that does not project out of the ellipsoid structure and a C-terminal helical turn in place of the C-terminal helix α4. Yet, it is more rigid than the F-actin binding site of Leishmania donovani cofilin. Experimental observations and structural features do not support the interaction of PIP2 with TgADF, and PIP2 does not affect the interaction of TgADF with G-actin. Overall, this study suggests that conformational flexibility of G-actin binding sites enhances the affinity of TgADF for G-actin, while conformational rigidity of F-actin binding sites of conventional ADF/cofilins is necessary for stable binding to F-actin.

[The importance of model organisms to study cilia and flagella biology]

Cilia and flagella are ubiquitous organelles that protrude from the surfaces of many cells, and whose architecture is highly conserved from protists to humans. These complex organelles, composed of over 500 proteins, can be either immotile or motile. They are involved in a myriad of biological processes, including sensing (non-motile cilia) and/or cell motility or movement of extracellular fluids (motile cilia). The ever-expanding list of human diseases linked to defective cilia illustrates the functional importance of cilia and flagella. These ciliopathies are characterised by an impressive diversity of symptoms and an often complex genetic etiology. A precise knowledge of cilia and flagella biology is thus critical to better understand these pathologies. However, multi-ciliated cells are terminally differentiated and difficult to manipulate, and a primary cilium is assembled only when the cell exits from the cell cycle. In this context the use of model organisms, that relies on the high degree of structural but also of molecular conservation of these organelles across evolution, is instrumental to decipher the many facets of cilia and flagella biology. In this review, we highlight the specific strengths of the main model organisms to investigate the molecular composition, mode of assembly, sensing and motility mechanisms and functions of cilia and flagella. Pioneering studies carried out in the green alga Chlamydomonas established the link between cilia and several genetic diseases. Moreover, multicellular organisms such as mouse, zebrafish, Xenopus, C. elegans or Drosophila, and protists like Paramecium, Tetrahymena and Trypanosoma or Leishmania each bring specific advantages to the study of cilium biology. For example, the function of genes involved in primary ciliary dyskinesia (due to defects in ciliary motility) can be efficiently assessed in trypanosomes.

Leishmania actin binds and nicks kDNA as well as inhibits decatenation activity of type II topoisomerase

Leishmania actin (LdACT) is an unconventional form of eukaryotic actin in that it markedly differs from other actins in terms of its filament forming as well as toxin and DNase-1-binding properties. Besides being present in the cytoplasm, cortical regions, flagellum and nucleus, it is also present in the kinetoplast where it appears to associate with the kinetoplast DNA (kDNA). However, nothing is known about its role in this organelle. Here, we show that LdACT is indeed associated with the kDNA disc in Leishmania kinetoplast, and under in vitro conditions, it specifically binds DNA primarily through electrostatic interactions involving its unique DNase-1-binding region and the DNA major groove. We further reveal that this protein exhibits DNA-nicking activity which requires its polymeric state as well as ATP hydrolysis and through this activity it converts catenated kDNA minicircles into open form. In addition, we show that LdACT specifically binds bacterial type II topoisomerase and inhibits its decatenation activity. Together, these results strongly indicate that LdACT could play a critical role in kDNA remodeling.

Characterization of a subunit of the outer dynein arm docking complex necessary for correct flagellar assembly in Leishmania donovani

Background

In order to proceed through their life cycle, Leishmania parasites switch between sandflies and mammals. The flagellated promastigote cells transmitted by the insect vector are phagocytized by macrophages within the mammalian host and convert into the amastigote stage, which possesses a rudimentary flagellum only. During an earlier proteomic study of the stage differentiation of the parasite we identified a component of the outer dynein arm docking complex, a structure of the flagellar axoneme. The 70 kDa subunit of the outer dynein arm docking complex consists of three subunits altogether and is essential for the assembly of the outer dynein arm onto the doublet microtubule of the flagella. According to the nomenclature of the well-studied Chlamydomonas reinhardtii complex we named the Leishmania protein LdDC2.

Methodology/Principal Findings

This study features a characterization of the protein over the life cycle of the parasite. It is synthesized exclusively in the promastigote stage and localizes to the flagellum. Gene replacement mutants of lddc2 show reduced growth rates and diminished flagellar length. Additionally, the normally spindle-shaped promastigote parasites reveal a more spherical cell shape giving them an amastigote-like appearance. The mutants lose their motility and wiggle in place. Ultrastructural analyses reveal that the outer dynein arm is missing. Furthermore, expression of the amastigote-specific A2 gene family was detected in the deletion mutants in the absence of a stage conversion stimulus. In vitro infectivity is slightly increased in the mutant cell line compared to wild-type Leishmania donovani parasites.

Conclusions/Significance

Our results indicate that the correct assembly of the flagellum has a great influence on the investigated characteristics of Leishmania parasites. The lack of a single flagellar protein causes an aberrant morphology, impaired growth and altered infectiousness of the parasite.

Leishmania parasites are responsible for the disease leishmaniasis. They are spread through sandflies. The primary hosts are mammals, including humans. They occur in two different morphological forms. The flagellated promastigotes live in the gut of the sandfly vector. After transmission to the mammalian host they get phagocytized by macrophages and convert into the amastigote form, which is able to survive within the phagolysosome. The molecular mechanisms underlying this transformation process from promastigote to amastigote are poorly understood so far. A striking difference of the life cycle stages is a long flagellum in the promastigote compared to only a rudimentary flagellum in the mammalian stage amastigote. During an earlier study of the stage differentiation of Leishmania donovani we identified a flagellar protein, a subunit of the outer dynein arm docking complex (ODA-DC2). This protein is part of a flagellar structure called the axoneme. Here we have further characterized the protein regarding its role within the life cycle of the parasite. Mutant promastigotes lacking DC2 protein show reduced flagellar length and a more amastigote-like appearance overall. In addition, the motility is heavily retrenched and transmission electron microscopy indicated that the flagellar ultrastructure is affected. Furthermore, the mutants express amastigote-specific genes and show increased in vitro infectiousness towards macrophages. Therefore, we conclude that the correct assembly of the flagellum is vital for maintenance of the promastigote stage of the parasite.

Actin-depolymerizing factor of second-generation merozoite in Eimeria tenella: clone, prokaryotic expression, and diclazuril-induced mRNA expression

Actin depolymerizing factor (ADF) is an essential actin-binding protein that plays a key role in the control of actin dynamics and actin-based motility processes in intracellular parasites. To determine the effects of diclazuril on ADF gene of second-generation merozoites (mz-ADF) mRNA expression in Eimeria tenella, mz-ADF gene was cloned by RT-PCR from extracted RNA in second-generation merozoite of E. tenella and successfully expressed by pET-28a vector in Escherichia coli BL21(DE3). Results showed that the full length of the cloned cDNA sequence of the mz-ADF gene is 476 bp including an ORF of 375 bp. The sequence has 100% homology with a published sequence of sporozoite stage E. tenella ADF mRNA (GenBank EF195234.1). The recombinant protein was induced to be expressed by 1 mM isopropyl beta-D: -1-thiogalactopyranoside in vitro. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis showed that 16.99 kDa fusion protein existed in solvable form. Compared with the infected/control group, mz-ADF mRNA expression level was downregulated by 63.86% in the infected/treatment group with the treatment of diclazuril. In conclusion, the data presented here indicate that mz-ADF gene participates in an important role in the invasion host of E. tenella. Downregulation of mz-ADF mRNA expression enrich the mechanism study of diclazuril on E. tenella.

The paraflagellar rod of kinetoplastid parasites: from structure to components and function

The role of the eukaryotic flagellum in cell motility is well established but its importance in many other aspects of cell biology, from cell signalling to developmental regulation, is becoming increasingly apparent. In addition to this diversity of function the core structure of the flagellum, which has been inherited from the earliest ancestor of all eukaryotes, is embellished with a range of extra-axonemal structures in many organisms. One of the best studied of these structures is the paraflagellar rod of kinetoplastid protozoa in which the morphological characteristics have been well defined and some of the major protein constituents have been identified. Here we discuss recent advances in the identification of further molecular components of the paraflagellar rod, how these impact on our understanding of its function and regulation and the implications for therapeutic intervention in a number of devastating human pathologies.

Actin-interacting and flagellar proteins in Leishmania spp.: Bioinformatics predictions to functional assignments in phagosome formation

Several motile processes are responsible for the movement of proteins into and within the flagellar membrane, but little is known about the process by which specific proteins (either actin-associated or not) are targeted to protozoan flagellar membranes. Actin is a major cytoskeleton protein, while polymerization and depolymerization of parasite actin and actin-interacting proteins (AIPs) during both processes of motility and host cell entry might be key events for successful infection. For a better understanding the eukaryotic flagellar dynamics, we have surveyed genomes, transcriptomes and proteomes of pathogenic Leishmania spp. to identify pertinent genes/proteins and to build in silico models to properly address their putative roles in trypanosomatid virulence. In a search for AIPs involved in flagellar activities, we applied computational biology and proteomic tools to infer from the biological meaning of coronins and Arp2/3, two important elements in phagosome formation after parasite phagocytosis by macrophages. Results presented here provide the first report of Leishmania coronin and Arp2/3 as flagellar proteins that also might be involved in phagosome formation through actin polymerization within the flagellar environment. This is an issue worthy of further in vitro examination that remains now as a direct, positive bioinformatics-derived inference to be presented.