Biochemical analysis of membrane proteins from an early maturation stage of phagosomes

Magnetic Patterning of Vorticella convallaria in a Microfluidic Device

We describe an inexpensive magnetic cell patterning method as a tool for protozoologists. The ciliate Vorticella convallaria is useful for various biofluidics applications. Here, we show that V. convallaria will ingest metal beads and that permanent magnets can be used to pattern cells in Petri dishes or a microfluidic device. Patterning is reversibly achieved by placing magnets at the point of desired cell attachment. Analogous magnetic manipulation could be performed using other phagocytic cells.

Tetrahymena phagocytic vesicles as ecological micro-niches of phage transfer

The microbial communities in natural environments such as soil, pond water, or animal rumens are composed of a diverse mixture of bacteria and protozoa including ciliates or flagellates. In such microbiomes, a major source of bacterial mortality is grazing by phagocytic protists. Many protists are omnivorous heterotrophs, feeding on a range of different bacterial species. Due to this indiscriminate feeding, different bacterial species can assemble together in the same phagocytic vesicles where they can potentially exchange genetic material. Here we show that Tetrahymena thermophila imports and accumulates phage donor and recipient bacterial strains in its phagocytic vesicles and that under laboratory conditions the ingested bacteria remain viable for ≥2 h. Prophages in the ingested bacteria induce immediately after ingestion, and the released phages are concentrated in the phagocytic vesicles of the ciliate. These phages retain their ability to infect phage-susceptible bacterial strains. As a consequence of being confined within the phagosome, the frequency of lysogen formation in these vesicles increases 6-fold as compared with the bulk solution. Collectively, these observations suggest that T. thermophila aids in dissemination of bacteriophages by accumulating susceptible bacteria and phages in their phagocytic vesicles.

Calcium signaling in closely related protozoan groups (Alveolata): non-parasitic ciliates (Paramecium, Tetrahymena) vs. parasitic Apicomplexa (Plasmodium, Toxoplasma)

The importance of Ca2+-signaling for many subcellular processes is well established in higher eukaryotes, whereas information about protozoa is restricted. Recent genome analyses have stimulated such work also with Alveolates, such as ciliates (Paramecium, Tetrahymena) and their pathogenic close relatives, the Apicomplexa (Plasmodium, Toxoplasma). Here we compare Ca2+ signaling in the two closely related groups. Acidic Ca2+ stores have been characterized in detail in Apicomplexa, but hardly in ciliates. Two-pore channels engaged in Ca2+-release from acidic stores in higher eukaryotes have not been stingently characterized in either group. Both groups are endowed with plasma membrane- and endoplasmic reticulum-type Ca2+-ATPases (PMCA, SERCA), respectively. Only recently was it possible to identify in Paramecium a number of homologs of ryanodine and inositol 1,3,4-trisphosphate receptors (RyR, IP3R) and to localize them to widely different organelles participating in vesicle trafficking. For Apicomplexa, physiological experiments suggest the presence of related channels although their identity remains elusive. In Paramecium, IP3Rs are constitutively active in the contractile vacuole complex; RyR-related channels in alveolar sacs are activated during exocytosis stimulation, whereas in the parasites the homologous structure (inner membrane complex) may no longer function as a Ca2+ store. Scrutinized comparison of the two closely related protozoan phyla may stimulate further work and elucidate adaptation to parasitic life. See also "Conclusions" section.

A bioreactor model system specifically designed for Tetrahymena growth and cholesterol removal from milk

This work describes the configuration and operation of a bioreactor system especially designed for Tetrahymena cultivation and its use for milk improvement, particularly cholesterol elimination by the action of this cell. An advantage of the proposed method is the re-use of the growth medium; thus, the medium is used twice to provide two batches of Tetrahymena biomass without the need of further inoculation. This makes the procedure of producing the cell biomass faster and more economical. Cells are concentrated in the culture vessels by sedimentation at room temperature and then transferred to milk suspensions, where they can further grow for at least one generation with the benefit of reducing steeply cholesterol level. Milk treated according to this process is separated from the biomass by centrifugation. Under these conditions, less than 5% of the cells remain in the milk, and cholesterol elimination amounts to 75 +/- 10% of that initially present. No changes in sensorial properties of the milk, such as clotting or butyric odor, were observed as a result of this treatment. In addition, the bioreactor allows the aseptic recovery of the spent growth medium, which contains diverse enzymes of interest, and the cell pellets, to exploit particular lipids like phosphonolipids, abundant poly-unsaturated fatty acids and co-enzyme Q(8).

The Tetrahymena thermophila phagosome proteome

In vertebrates, phagocytosis occurs mainly in specialized cells of the immune system and serves as a primary defense against invading pathogens, but it also plays a role in clearing apoptotic cells and in tissue remodeling during development. In contrast, unicellular eukaryotes, such as the ciliate Tetrahymena thermophila, employ phagocytosis to ingest and degrade other microorganisms to meet their nutritional needs. To learn more about the protein components of the multistep process of phagocytosis, we carried out an analysis of the Tetrahymena phagosome proteome. Tetrahymena cells were fed polystyrene beads, which allowed for the efficient purification of phagosomes. The protein composition of purified phagosomes was then analyzed by multidimensional separation coupled with tandem mass spectrometry. A total of 453 peptides were identified that resulted in the identification of 73 putative phagosome proteins. Twenty-eight of the proteins have been implicated in phagocytosis in other organisms, indicating that key aspects of phagocytosis were conserved during evolution. Other identified proteins have not previously been associated with phagocytosis, including some of unknown function. Live-cell confocal fluorescence imaging of Tetrahymena strains expressing green fluorescent protein-tagged versions of four of the identified phagosome proteins provided evidence that at least three of the proteins (including two with unknown functions) are associated with phagosomes, indicating that the bulk of the proteins identified in the analyses are indeed phagosome associated.

Column chromatographic prefractionation leads to the detection of 543 different gene products in human fetal brain

In a previous publication a large series of proteins were identified in fetal human brain by the use of two-dimensional electrophoresis (2-DE) with subsequent matrix-assisted laser desorption/ionization-time of flight (MALDI-TOF) and MALDI-tandem time-of-flight (TOF/TOF) analysis. Further identification of many more different spots by traditional 2-DE without additional step such as narrow immobilized ph gradient (IPG) strips or prefractionation seems unlikely and we therefore decided to separate extracted brain proteins by ion-exchange chromatography using a TSK gel DEAE-5PW column followed by 2-DE of individual fractions and analysis by MALDI-TOF/TOF with LIFT technology in fetal brain of the early second trimester. About 1880 protein spots corresponding to 543 different gene products were identified. These proteins included housekeeping, signaling, cytoskeletal, metabolic, antioxidant, and neuron/synaptosomal specific proteins. Among these, 314 gene products (314/543, 57.8%), which have never been detected in traditional 2-DE of human fetal brain, were observed by this method. This updated map of fetal brain proteins may serve as data base and reference map for fetal brain proteins, and the methodology applied may be used as a valuable analytical tool for the basis of protein expressional studies in health and disease.

Characterization of Endocytic Vesicles Using Magnetic Microbeads Coated with Signalling Ligands

Iron microbeads coated with the protein ligands insulin and EGF (Fe-INS and Fe-EGF) were prepared. Examination of the traffic of these ligand-coated microbeads demonstrated their internalization via clathrin-coated vesicles. Using magnetic methods, we have purified vesicles derived from the endocytic pathway. Vesicles prepared by this method are essentially free of contamination with other endomembrane compartments. Examination of the vesicles derived from cells treated with Fe-INS beads demonstrated the presence of the components of the Ras/Erk cascade on their surface. We conclude that the coupling of the Erk-signalling cascade induced by insulin takes place on the surface of endocytic vesicles derived from the internalization of the insulin receptor.

Molecular Aspects of Membrane Trafficking in Paramecium

Results achieved in the molecular biology of Paramecium have shed new light on its elaborate membrane trafficking system. Paramecium disposes not only of the standard routes (endoplasmic reticulum --> Golgi --> lysosomes or secretory vesicles; endo- and phagosomes --> lysosomes/digesting vacuoles), but also of some unique features, e.g. and elaborate phagocytic route with the cytoproct and membrane recycling to the cytopharynx, as well as the osmoregulatory system with multiple membrane fusion sites. Exocytosis sites for trichocysts (dense-core secretory vesicles), parasomal sacs (coated pits), and terminal cisternae (early endosomes) display additional regularly arranged predetermined fusion/fission sites, which now can be discussed on a molecular basis. Considering the regular, repetitive arrangements of membrane components, availability of mutants for complementation studies, sensitivity to gene silencing, and so on, Paramecium continues to be a valuable model system for analyzing membrane interactions. This review intends to set a new baseline for ongoing work along these lines.

Proteomics--post-genomic cartography to understand gene function

The completion of the genomic sequences of numerous organisms from human and mouse to Caenorhabditis elegans and many microorganisms, and the definition of their genes provides a database to interpret cellular protein-expression patterns and relate them to protein function. Proteomics technologies that are dependent on mass spectrometry and involve two-dimensional gel electrophoresis are providing the main window into the world of differential protein-expression analysis. In this article, the limitations and expectations of this research field are examined and the future of the analytical needs of proteomics is explored.

Calcium in ciliated protozoa: sources, regulation, and calcium-regulated cell functions

In ciliates, a variety of processes are regulated by Ca2+, e.g., exocytosis, endocytosis, ciliary beat, cell contraction, and nuclear migration. Differential microdomain regulation may occur by activation of specific channels in different cell regions (e.g., voltage-dependent Ca2+ channels in cilia), by local, nonpropagated activation of subplasmalemmal Ca stores (alveolar sacs), by different sensitivity thresholds, and eventually by interplay with additional second messengers (cilia). During stimulus-secretion coupling, Ca2+ as the only known second messenger operates at approximately 5 microM, whereby mobilization from alveolar sacs is superimposed by "store-operated Ca2+ influx" (SOC), to drive exocytotic and endocytotic membrane fusion. (Content discharge requires binding of extracellular Ca2+ to some secretory proteins.) Ca2+ homeostasis is reestablished by binding to cytosolic Ca2+-binding proteins (e.g., calmodulin), by sequestration into mitochondria (perhaps by Ca2+ uniporter) and into endoplasmic reticulum and alveolar sacs (with a SERCA-type pump), and by extrusion via a plasmalemmal Ca2+ pump and a Na+/Ca2+ exchanger. Comparison of free vs total concentration, [Ca2+] vs [Ca], during activation, using time-resolved fluorochrome analysis and X-ray microanalysis, respectively, reveals that altogether activation requires a calcium flux that is orders of magnitude larger than that expected from the [Ca2+] actually required for local activation.

Two-dimensional electrophoresis of membrane proteins using immobilized pH gradients

Two-dimensional electrophoresis (2-DE) is a highly resolving technique for arraying proteins by isoelectric point and molecular mass. To date, the resolving ability of 2-DE for protein separation is unsurpassed, thus ensuring its use as the fundamental separation method for proteomics. When immobilized pH gradients (IPGs) are used for isoelectric focusing in the first dimension, excellent reproducibility and high protein load capacity can be achieved. While this has been beneficial for separations of soluble and mildly hydrophobic proteins, separations of membrane proteins and other hydrophobic proteins with IPGs have often been poor. Stimulated by the growing interest in proteomics, recent developments in 2-DE methodology have been aimed at rectifying this situation. Improvements have been made in the area of protein solubilization and sample fractionation, leading to a revamp of traditional approaches for 2-DE of membrane proteins. This review explores these developments.

The dynamic range of protein expression: a challenge for proteomic research

Proteomic research, for its part, is benefiting enormously from the last decade of genomic research as we now have archived, annotated and audited sequence databases to correlate and query experimental data. While the two-dimensional electrophoresis (2-DE) gels are still a central part of proteomics, we reflect on the possibilities and realities of the current 2-DE technology with regard to displaying and analysing proteomes. Limitations of analysing whole cell/tissue lysates by 2-DE alone are discussed, and we investigate whether extremely narrow p/ranges (1 pH unit/25 cm) provide a solution to display comprehensive protein expression profiles. We are confronted with a challenging task: the dynamic range of protein expression. We believe that most of the existing technology is capable of displaying many more proteins than is currently achievable by integrating existing and new techniques to prefractionate samples prior to 2-DE display or analysis. The availability of a "proteomics toolbox", consisting of defined reagents, methods, and equipment, would assist a comprehensive analysis of defined biological systems.