Plasma membrane biogenesis

GORDESKY MARINETTI, 1973 HAEST 6e DEUTICKE, 1976). It should be noted that the major phospholipids of the endoplasmic reticulum are distributed in the opposite way (DePIERRE 6e DALLNER, 1975). This finding might lend support to the theory of plasma membrane biogenesis from the endoplasmic reticulum. There is some question about the distribution of one major membrane lipid, cholesterol. 

PLASMA MEMBRANE BIOGENESIS IN HIGHER PLANTS THE LIPID ROUTES... 

The lateral diffusion could also be involved in plasma membrane biogenesis the phospholipids could move in the plane of a membrane, and then, through a transient interconnection, reach a new membrane. As in the preceding mechanisms there is still a lack of in vivo evidence (2,3). 

It is remarkable, as far as lipids are concerned, that there are so many well-designed hypotheses supported by so few conclusive data and this discrepancy is probably one of the challenges to be faced in the next decade in order to improve our knowledge on plasma membrane biogenesis in higher plants. In addition, these mechanisms, even if they can be taken for established, are not likely to coexist at the same rate throughout the cell life, or to involve the different lipid classes at the same extent in the various domains of the... 

Basically, the strategy for studying the lipid routes of plasma membrane biogenesis implies that two complementary approaches be developed at the same time ... 

The complexity of the processes involved in plasma membrane biogenesis probably exceeds the possibilities of the mere in vivo analysis. In theory, cell-free systems should facilitate the study of the individual steps of the interaction between the various cell comparments. ROTHMAN et al. (11) provided the first evidence of the feasability of the approach and, recently, NOWACK et al. (12) described a cell-free system able to give informations on the budding from ER and the vesicle fusion with the GA. This system is suitable for the study of protein transfer, but could also be adapted to the case of the lipids. 

In conclusion, all of these approaches aiming to investigate the overall plasma membrane biogenesis from the biosynthesis of the lipid enzymes, to the insertion of their products into the plasmalemma, may help to shed some light on the lipid routes, for which so much has been supposed and so little is known. 

Plasma membrane biogenesis in higher plants in vivo transfer of lipids to the plasma membrane. Phytochemistry 22, 1631-1638. 

Plasma membrane biogenesis in eukaryotic cells translocation of newly synthesized lipids. Proc. Natl. Acad. Sci. USA Si, 1385-1388. 

Lipids are transported between membranes. As indicated above, lipids are often biosynthesized in one intracellular membrane and must be transported to other intracellular compartments for membrane biogenesis. Because lipids are insoluble in water, special mechanisms must exist for the inter- and intracellular transport of membrane lipids. Vesicular trafficking, cytoplasmic transfer-exchange proteins and direct transfer across membrane contacts can transport lipids from one membrane to another. The best understood of such mechanisms is vesicular transport, wherein the lipid molecules are sorted into membrane vesicles that bud out from the donor membrane and travel to and then fuse with the recipient membrane. The well characterized transport of plasma cholesterol into cells via receptor-mediated endocytosis is a useful model of this type of lipid transport. [9, 20]. A brain specific transporter for cholesterol has been identified (see Chapter 5). It is believed that transport of cholesterol from the endoplasmic reticulum to other membranes and of glycolipids from the Golgi bodies to the plasma membrane is mediated by similar mechanisms. The transport of phosphoglycerides is less clearly understood. Recent evidence suggests that net phospholipid movement between subcellular membranes may occur via specialized zones of apposition, as characterized for transfer of PtdSer between mitochondria and the endoplasmic reticulum [21]. 

Figure 2. General topological feature of PS translocation and decarboxylation in mammalian cells. PS is synthesized by PSS I and II in endoplasmic reticulum (ER) or mitochondria-associated membrane (MAM). The nascent PS is transported other membranes such as plasma membrane, nucleus, and mitochondria. The PS transported to the mitochondrial outer membrane is then translocated to the inner membrane, in which PS is converted to PE by PS decarboxylase (PSD). The PE formed in mitochondria is dynamic and can be exported to other organelles for membrane biogenesis.

There is at present no precise information concerning either the control mechanisms that govern wall-biogenesis or the interactions between wall biogenetic-processes and general cellular metabolism. The number of steps involved in the formation of a polysaccharide from a glycosyl-nucleotide is not known, and it is not clear how cellular control is extended beyond the plasma membrane, or how the cell wall is formed from the component polymers. Thus, it appears that the major questions posed by the problem of cell-wall biosynthesis have yet to be answered (see also, Ref. 217). 

Carafoli, E., 1994, Biogenesis plasma membrane calcium ATPase 15 years of work on the purified enzyme. Faseb J 8, 993-1002. 

Neurotransmission is based on the secretion of neurotransmitters from secretory vesicles in the presynaptic membrane and the binding of the agonists by receptors on the postsynaptic membrane. The transmitters have to travel only about 20 nm across the synaptic cleft, whereas neurohormones may act on much more distant receptors. The biogenesis of the secretory vesicles and the receptors are intimately connected with the secretory pathway of the eukaryotic cells. In this system a series of membrane-bound structures mediate the transfer of exported proteins from their site of synthesis at the rough endoplasmic reticulum to their site of discharge at the plasma membrane. We will use the chromaffin granules (storage vesicles of the adrenal medulla) as an example for secretory vesicles, and the acetylcholine receptor for receptors of neurotransmitters. 

The biogenesis of both acetylcholine receptor and chromaffin granules share several common properties. The specific polypeptides are synthesized and transported into the membrane by a vectorial translation process. The specific proteins are sorted out by the Golgi apparatus and eventually fuse with the plasma membrane via the secretory pathway. Yet the acetylcholine receptor functions on the plasma membrane, and therefore it should stay on this membrane for a long time (2-7 days). On the other hand, the function of chromaffin granules is to store neurotransmitters. Therefore they stay most of their lifetime inside the cell and their fusion with the plasma membrane is temporary. Soon after the secretion process, the constituents of the chromaffin granule membrane must be removed from the plasma membrane by endocytosis. 

Zak, E., Norling, B., Maitra, R., Huang, F., Anderson, B., andPakrasi, H. B. 2001. The initial steps of biogenesis of cyanobacterial photosystems occur in plasma membranes. Proc. Nalt. Acad. Sci. USA. 23,13443-13448. 

The biogenesis of LPS is a complex process involving various steps that occur at the plasma membrane followed by the translocation of LPS molecules to the bacterial cell surface. LPS biosynthesis employs a large number of enzymes. The core OS is assembled on preformed lipid A by sequential glycosyl transfer of monosaccharides, while the O antigen is independently assembled on undecaprenyl-phosphate (Und-P), a... 

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