The lysosomal compartment as a whole consists of a collection of vacuoles of heterogeneous composition, morphology, location, and density. The heterogeneity is due to the diversity of cargo and the existence of several feeder pathways of which the classical endosome pathway is a major one. Heterogeneity is also generated by the varying degree of cargo degradation within individual vacuoles, and by fusion events between the various vacuoles. The classical lysosomes of high buoyant density and high hydrolase content correspond to the end point of the degradation process. They serve in part as storage vacuoles for lysosomal components ready to be redeployed. These components include the hydrolases, the limiting membrane protected by LAMPs, and other substances resistant to degradation. They also contain slowly degraded lumenal lipids often present as multilamellar membrane whirls.
Membrane Separation Process By Kaushik Nath Pdf 155
Early studies in yeast showed that the Rab7 orthologue, Ypt7p, was required for delivery of degradative cargo to the vacuole, that is, to the yeast lysosome (Wichmann et al, 1992; Schimmoller and Riezman, 1993). Subsequent studies in mammalian cells demonstrated that expression of dominant negative mutants of Rab7 results in dispersal of endosomes, a block in cargo trafficking to the lysosomes, and the deterioration of lysosome acidification and functionality (Bucci et al, 2000). By recruiting a variety of effector proteins on LEs, Rab7/Ypt7p coordinates various maturation processes, and renders the organelle capable of fusion with other LEs as well as lysosomes (or the vacuole in yeast). In addition, in yeast, Ypt7p is known to be directly involved in the assembly of the fusion machinery at both the LEs and the vacuole membrane (Haas et al, 1995; Ostrowicz et al, 2008).
PIKfyve has also been linked to the regulation of ion channels, mostly by controlling their localization at the plasma membrane by exocytosis (Shisheva, 2008). In addition, PIKfyve may directly regulate the activity of channels in LEs. The calcium permeable cation channel TRPML1 was recently demonstrated to be directly activated by the presence of PtdIns(3,5)P(2) enabling the efflux of Ca2+ (Dong et al, 2010). Ca2+ is known to have an important regulatory function in homotypic and heterotypic fusions of LEs and lysosomes/vacuoles as well as in reformation of lysosomes from endolysosomes (Luzio et al, 2007a). The localized production of PtdIns(3,5)P(2) on endosomal membranes thus allows the control of channel activity in confined regions and may enable regulation of LE fusion/fission in a spatio-temporal manner. It is plausible that the highly vacuolated phenotype of PIKfyve/Fab1p mutants is partially the result of osmotic swelling or deregulated fusion/fission processes induced by the misregulation of endosomal ion channels (Shisheva, 2008).
A recent study contradicts the view of dynein as the major motor protein in transport of LEs towards the minus end of microtubules (Loubery et al, 2008). The authors argue for an indirect role in regulating the actin cytoskeleton. The actin cytoskeleton, well known for its various roles in endocytosis (Kaksonen et al, 2006), seems indeed to have a role in the endosomal degradative pathway. It has been long known that disruption of the actin cytoskeleton results in a block of cargo transport from EEs to LEs (Gruenberg et al, 1989); however, the actual function of actin has remained unclear. A series of recent studies have, however, shed some light on to the matter by indicating that Arp2/3-driven actin nucleation occurs on EEs and is required for a number of membrane fission processes (Derivery et al, 2009; Gomez and Billadeau, 2009; Morel et al, 2009; Duleh and Welch, 2010). These include sorting and vesicle fission in the recycling pathway, and cargo transport to the TGN and lysosomes. Members of the annexin family of proteins, such as annexins A2 and A8, link actin to endosome membranes (Goebeler et al, 2008; Morel et al, 2009). Annexin A2 was shown to have a role in LE biogenesis, perhaps by regulating fission from EEs.
Microautophagy is a process in which cytosolic components are taken up through invaginations of LEs, in both a selective and unselective manner (Figure 7B). Selective microautophagy involves the cytosolic chaperone hsc70 and the ESCRT-I and ESCRT-III complexes, which together allow uptake of cytosolic proteins that bear a KFERQ sequence motif (Sahu et al, 2011). This is thought to rely on the electrostatic association of hsc70 with phosphatidylserine in the cytosolic leaflet of the LE membrane. A similar process has, interestingly, been proposed for the inclusion of certain RNAs into ILVs (Valadi et al, 2007; Gibbings and Voinnet, 2010).
This research gave a new dimension to microalgae cultivation using nanoemulsion composed of two different oils. In the future, other potential biocompatible oils can be explored for increasing the biomass of microalgae. The next step would be to test it with actual sources of CO2 such as flue gas. Recyclability of nanoemulsions could also save cost and energy. Energy recovered by recycling the emulsion can be compared with energy given during the centrifugation of the nanoemulsion extraction process. These energy calculations can help to define a scale for nanoemulsion-based technology. Secondly, less energy-intensive nanoemulsion separation technology from microalgal biomass could help to scale this process. 2ff7e9595c
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