Secretion, of proteins

Burgess TL, Kelly RB (1987) Constitutive and regulated secretion of proteins. Annu Rev Cell Biol 3 243-293... 

P. fluorescens has well-developed mechanisms for the secretion of proteins into the periplasm which facilitates S—S bond formation and proper N-terminal processing. It also allows one to reduce the formation of inclusion bodies and, thus, the additional costs caused by refolding processes. Proteolytic degradation of the expressed protein is also low, and very high... 

Simple plants Physcomitrella patens Chlamydomonas reinhardtii Lemna minor Containment, clonal propagation, batch consistency, secretion of proteins into medium, regulatory compliance, homologous recombination in Physcomitrella Scalability... 

E. coli strains. E. coli 0157 H7 strains lack efal, but do encode toxB, a tnmcated version of the efal gene. A toxB mutant exhibits reduced adherence to cultured epithelial cells (Stevens et ah, 2004). However, toxB had an indirect effect on adherence to epithelial cells by modulating the production and secretion of proteins that play a role for A/E formation in EHEC. The receptors for Efal and ToxB have not been identified and their true role in vivo is unknown. 

Cerulenin inhibits formation of polyisoprenol, probably by uncom-petitively inhibiting HMG-CoA synthetase.250 It strongly inhibited production of Rous-sarcoma virus by infected, chick-embryo cells, but an effect on the viral glycoproteins was not observed.251 Other effects of cerulenin, such as its inhibition of fatty acid synthesis, may have caused inhibition of virus production. The inhibition, by cerulenin, of secretion of proteins by bacilli has been noted for some time, but no satisfactory explanation has as yet been offered (see Ref. 252, and ref-... 

A major goal in recombinant DNA technology is the production of useful foreign proteins by bacteria, yeast, or other cultured cells. Protein synthesis depends upon both transcription and translation of the cloned genes and may also involve secretion of proteins from the host cells. The first step, transcription, is controlled to a major extent by the structures of promoters and other control elements in the DNA (Chapter 28). Since eukaryotic promoters often function poorly in bacteria, it is customary to put the cloned gene under the control of a strong bacterial or viral X promoter. The latter include the X promoter PL (Fig. 28-8) and the lac (Fig. 28-2) and trp promoters of E. coli. These are all available in cloning vehicles. 

Exocytosis is the secretion of proteins out of the cell across the plasma membrane into the extracellular space. Proteins destined to be secreted are synthesized on ribosomes bound to the RER membrane and are then transported in membrane-bound vesicles to the Golgi apparatus where they are sorted and packaged up into secretory vesicles. All cells continuously secrete proteins via the constitutive pathway, whereas only specialized cells (e.g. of the pancreas, nerve cells) secrete proteins via the regulated secretory pathway in response to certain stimuli. 

Fig. 1. A model for the pleiotropic effects of LH on functions of Leydig cells. LH interacts with its specific receptor in the plasma membrane of the Leydig cell which results in the activation of several transducing systems and the formation of several second messengers (cyclic AMP, Ca2+, diacylglycerol and arachidonic acid metabolites). Protein kinases (A, C and calmodulin dependent) are activated resulting in the phosphorylation of specific proteins and the synthesis of specific proteins. The (phospho)proteins are involved in the transport of cholesterol to, and the control of, cholesterol metabolism in the inner mitochondrial membrane. Arachidonic acid metabolites (prostaglandins, leukotrienes) may also control steroidogenesis. LH can also regulate the secretion of proteins. The trophic effects of LH are manifested in the growth and differentiation of the Leydig cells.

Fig. 1-7 Possible membrane-exchange pathways during secretion of protein from a cell.

Lipid raft domains of plasma membranes are enriched in cholesterol and sphingolipids. As a consequence, compounds that extract or sequester cholesterol, such as fS-cyclodextrins, nystatin, and filipin, can block selectively endocytosis of cholera toxin, GPI-linked proteins, and other receptors that associate with lipid rafts and caveolae. However, cholesterol is also critical for CME, secretion of proteins, and the actin network. Therefore, conditions designed to affect selectively raft-mediated endocytosis by perturbing cholesterol levels must be carefully controlled to avoid disrupting other mechanisms of endocytosis (40). 

Electron microscopy studies have revealed that choline deficiency results in disorganization of the structures of the ER and of the Golgi, a small organelle required for the secretion of proteins from the cell. Proteins destined for secretion are synthesized in the ER, Most such proteins are modified by covalent attachment... 

In diseases of the small intestine, active secretion caused by cyclic nucleotide stimulation can result in a large volume of water and electrolytes moving into the lumen. Additionally, enteric neuron activation of mast cells can increase intestinal capillary permeability and promote passive fluid secretion. Diseases that increase intestinal permeability can result in passive secretion of protein-rich fluid into the intestinal lumen. Active secretion of electrolytes and water is a feature of many diarrheal disorders and can be stimulated by bacterial enterotoxins. Several bacterial enterotoxins interact with intestinal epithelial cell membrane adenylate cyclase or guanylate cyclase, resulting in increased cAMP or cGMP. These, in turn, activate basolateral chloride channels, resulting in an increase in the luminal secretion of chloride, accompanied by sodium and followed by water (Gemmell 1984). Bacterial enterotoxins that stimulate cAMP include cholera toxin, Escherichia coli... 

Golgi complex. A complex and dynamic membranous organelle of eukaryotic cells. Golgi bodies function in the posttranslational modification (gly-cosylation) and secretion of proteins or insertion into membranes. Composed of cis, medial and trans compartments, as well as a less well defined trans-golgi network. ... 

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