Tandemly arranged repeats of a novel highly charged 16-amino-acid motif representing the major component of the sperm-tail-specific axoneme-associated protein family Dhmst101 form extended alpha-helical rods within the extremely elongated spermatozoa of Drosophila hydei

The apical annuli of Toxoplasma gondii are composed of coiled-coil and signalling proteins embedded in the inner membrane complex sutures

The apical annuli are among the most intriguing and understudied structures in the cytoskeleton of the apicomplexan parasite Toxoplasma gondii. We mapped the proteome of the annuli in Toxoplasma by reciprocal proximity biotinylation (BioID), and validated five apical annuli proteins (AAP1-5), Centrin2, and an apical annuli methyltransferase. Moreover, inner membrane complex (IMC) suture proteins connecting the alveolar vesicles were also detected and support annuli residence within the sutures. Super-resolution microscopy identified a concentric organisation comprising four rings with diameters ranging from 200 to 400 nm. The high prevalence of domain signatures shared with centrosomal proteins in the AAPs together with Centrin2 suggests that the annuli are related and/or derived from the centrosomes. Phylogenetic analysis revealed that the AAPs are conserved narrowly in coccidian, apicomplexan parasites that multiply by an internal budding mechanism. This suggests a role in replication, for example, to provide pores in the mother IMC permitting exchange of building blocks and waste products. However, presence of multiple signalling domains and proteins are suggestive of additional functions. Knockout of AAP4, the most conserved compound forming the largest ring-like structure, modestly decreased parasite fitness in vitro but had no significant impact on acute virulence in vivo. In conclusion, the apical annuli are composed of coiled-coil and signalling proteins assembled in a pore-like structure crossing the IMC barrier maintained during internal budding.

A novel sheathed surface organelle of the Helicobacter pylori cag type IV secretion system

Type I strains of Helicobacter pylori (Hp) use a type IV secretion system (T4SS), encoded by the cag pathogenicity island (cag-PAI), to deliver the bacterial protein CagA into eukaryotic cells and to induce interleukin-8 secretion. Translocated CagA is activated by tyrosine phosphorylation involving Src-family kinases. The mechanism and structural basis for type IV protein secretion is not well understood. We describe here, by confocal laser scanning microscopy and field emission scanning electron microscopy, a novel filamentous surface organelle which is part of the Hp T4SS. The organelle is often located at one bacterial pole but can be induced by cell contact also along the lateral side of the bacteria. It consists of a rigid needle, covered focally or completely by HP0527 (Cag7 or CagY), a VirB10-homologous protein. HP0527 is also clustered in the outer membrane. The VirB7-homologous protein HP0532 is found at the base of this organelle. These observations demonstrate for the first time by microscopic techniques a complex T4SS-associated, sheathed surface organelle reminiscent to the needle structures of bacterial type III secretion systems.

Immunization of mice with a TolA-like surface protein of Trypanosoma cruzi generates CD4(+) T-cell-dependent parasiticidal activity

The gene family encoding a trypomastigote-specific protein restricted to the part of the flagellum in contact with the cell body of the trypomastigote form of Trypanosoma cruzi has been isolated, characterized, and expressed in a baculovirus expression system. The gene family contains three tandemly repeated members that have 97 to 100% sequence identity. The predicted protein encoded by the gene family has both significant amino acid sequence identity and other physical and biological features in common with the TolA proteins of Escherichia coli and Pseudomonas aeruginosa. Based on these similarities, we have designated this gene family tolT. Immunization of mice with recombinant TolT generates a population of CD4(+) T lymphocytes that recognize T. cruzi-infected macrophages, resulting in the production of gamma interferon (IFN-gamma), which leads to NO production and a 50 to 60% reduction in parasite numbers compared to that seen with infected macrophages incubated with naive T cells. This population of T cells also produces both IFN-gamma and interleukin 2 (IL-2) but not IL-4 or IL-5 when incubated with spleen cells stimulated with TolT antigen, indicating that they are of the T-helper 1 type. T cells from mice chronically infected with T. cruzi also produce significant levels of IFN-gamma when cocultured with macrophages and either TolT protein or paraflagellar rod protein, indicating that both of these flagellar proteins produce positive T-cell responses in mice chronically infected with T. cruzi.

Cloning and characterization of KPL2, a novel gene induced during ciliogenesis of tracheal epithelial cells

To identify genes upregulated during the process of ciliated cell differentiation of airway epithelial cells, differential display was used to compare RNA from rat tracheal epithelial (RTE) cells cultured under conditions that inhibit/promote ciliated cell differentiation. Several partial complementary DNAs (cDNAs) were identified whose expression was regulated coordinately with ciliated cell differentiation. One of these, KPL2, detected a messenger RNA transcript of approximately 6 kb when used as a probe on Northern blots of RNA from ciliated cultures but was undetectable in RNA from nonciliated cultures. Sequencing of overlapping clones obtained by a modified rapid amplification of cDNA ends procedure generated a complete cDNA sequence that exhibited no significant homology to sequences in GenBank, indicating that KPL2 is a novel gene. Southern analysis demonstrated that KPL2 exists as a single-copy gene. KPL2 contains a long open reading frame predicted to code for a protein of > 200 kD. Several putative functional motifs are present in the protein, including a calponin homology domain, three nuclear localization signals, a consensus P-loop, and a proline-rich region, suggesting that KPL2 has a unique function. KPL2 was undetectable in heart and liver samples, but was expressed in brain and testis, tissues that contain axonemal structures. In seminiferous tubules of the testis, KPL2 expression was stage-specific and appeared to be highest in spermatocytes and round spermatids. During differentiation of RTE cells, the expression of KPL2 closely paralleled that of an axonemal dynein heavy chain. These results suggest that KPL2 plays an important role in the differentiation or function of ciliated cells in the airway.

Proteins with tandemly arranged repeats of a highly charged 16-amino-acid motif encoded by the Dhmst101 gene family are structural components of the outer sheath of the extremely elongated sperm tails of Drosophila hydei

Fruit fly species of the genus Drosophila show a remarkable variation in sperm length. Some of them produce gigantic sperm several times the total male body length. Sperm of Drosophila hydei, for example, are more than 20 mm long. Little is known about the advantage of such elongated sperm or about the proteins that stabilize their thin flagellar tails. Recently, two members of a novel gene family Dhmst101(1) and Dhmst101(2), whose gene products are associated with the sperm tail, were isolated and characterized. Here a third member of this gene family, Dhmst101(3), is described. It was previously demonstrated that all three genes are located in a single small cluster on chromosome 5 of D. hydei. They are located within 15 kb of genomic DNA, oriented in the same direction and transcribed testis-specifically. The encoded sperm tail-specific proteins are mainly composed of tandemly arranged repeats of a highly charged, cysteine-containing motif of 16 amino acids with the consensus sequence KKKCA/EEAAKKEKEAAE. Experiments with synthetic repeat monomers and dimers have demonstrated a tendency for alpha-helical rod formation, which increased strongly with an increase in repeat number. Therefore, Dhmst101 proteins with 7-60 repeats with regularly spaced cystein-residues are thus expected to form long alpha-helical rods cross-linked by numerous Cys-Cys bridges. Here we apply immunoelectron microscopy and monospecific antibodies, alpha-mst101, raised against the KKKCAEAAKKEKEAAE-motif to investigate the distribution of Dhmst101 proteins within the sperm tail of D. hydei. We show that Dhmst101 proteins are part of the outer sheath of the sperm tail where they presumably help to provide a tight but elastic envelope for the extremely extended spermatozoa of D. hydei.

The Drosophila don juan (dj) gene encodes a novel sperm specific protein component characterized by an unusual domain of a repetitive amino acid motif

We identified and characterized the don juan gene (dj) of Drosophila melanogaster. The don juan gene codes for a sperm specific protein component with an unusual repetitive six amino acid motif (DPCKKK) in the carboxy-terminal part of the protein. The expression of Don Juan is limited to male germ cells where transcription of the dj gene is initiated during meiotic prophase. But Western blot experiments indicate that DJ protein occurs just postmeiotically. Examination of transgenic flies bearing a dj-promoter-lacZ reporter construct revealed lacZ mRNA distribution resembling the expression pattern of the endogenous dj mRNA in the adult testes, whereas beta-galactosidase expression is exclusively present in postmeiotic germ cells. Thus, these observations strongly suggest that dj transcripts are under translational repression until in spermiogenesis. To study the function and subcellular distribution of DJ in spermiogenesis we expressed a chimaeric dj-GFP fusion gene in the male germline exhibiting strong GFP fluorescence in the liver testes, where only elongated spermatids are decorated. With regard to the characteristic expression pattern of DJ protein and its conspicuous repeat units possible functional roles are discussed.

Purification, partial characterization, and localization of Sak57, an acidic intermediate filament keratin present in rat spermatocytes, spermatids, and sperm

We have purified a 57 kDa protein (designated Sak57, for spermatogenic cell/sperm-associated keratin) from sodium dodecyl sulfate-beta-mercaptoethanol (SDS-beta ME)-dissociated outer dense fibers isolated from rat sperm tails. Internal protein sequence analysis of Sak57 yielded two 15-mer and 10-mer fragments with 70-100% homology to human, rat, and mouse keratins and corresponding to the 1A and 2A regions of the alpha-helical rod domain of keratins. A multiple antigenic peptide (MAP) was constructed using the 10-mer amino acid sequence KAQYEDIAQK (corresponding to the 2A region) and used as antigen for the production of polyclonal antibodies in rabbit. Anti-MAP sera were used for further analysis of the biochemical characteristics of Sak57 in testis and sperm tails using chromatofocusing, immunoblotting, and [32P] orthophosphate-labeling. We have found that rat testis displays two immunoreactive proteins: a soluble 83 kDa protein with pl range 5.9-6.3, regarded as a precursor, and both detergent-insoluble and soluble 57 kDa protein with pl range 5.0-5.9, corresponding to the mature form Sak57. The testicular soluble form was phosphorylated. Rat sperm tail samples displayed only the Sak57 detergent-insoluble form and its pl was more acidic (4.7-4.8). Whole-mount electron microscopy of negatively stained preparations of sperm-derived Sak57 resuspended in SDS-beta ME revealed a rod-shaped pattern. A decrease in the concentration of SDS-beta ME resulted in the side-by-side aggregation of rod-shaped Sak57 forming thick bundles. Indirect immunofluorescence was used to determine the localization of Sak57 in isolated outer dense fibers, epididymal sperm, spermatids, and pachytene spermatocytes. Confocal laser scanning microscopy was used to analyze the three-dimensional arrangement of Sak57 in pachytene spermatocytes. Isolated outer dense fiber and sperm tails displayed an immunoreactive product in the form of linear clusters. In elongating spermatids (steps 10-11), Sak57 immunoreactivity was predominant in the head region whereas pachytene spermatocytes displayed a cortical cytoplasmic distribution. Results of this study demonstrate that Sak57 has the characteristics of a keratin intermediate filament and is present during meiotic and postmeiotic stages of spermatogenesis.