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The secretory pathway of protein synthesis and ..

A lectin, previously designated the Man/GlcNAc-specific lectin or mannan-binding protein, is found in rat liver and plasma. Analysis of the structural requirements for oligosaccharide binding indicated that the specificity of this lectin is directed primarily at the 'core' and peptide region of glycopeptides. We have examined synthesis and secretion of the core-specific lectin by primary rat hepatocytes and a rat hepatoma, H-4-II-E, utilizing pulse labeling with [35S]methionine, immunoprecipitation with a monospecific rabbit antibody raised against the purified lectin, and analysis by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and fluorography. A post-translational modification occurs between 10 and 40 min of chase which results in an increase in the M(r) from 24,000 to 26,000. This modification is not due to asparagine-linked glycosylation or oligosaccharide processing. The kinetics of secretion are unusual. Secretion begins at 1 h of chase and proceeds linearly for approximately 8 h until a maximum of 70% of the lectin has been secreted. Secretion, but not the post-translational modification is inhibited by monensin. The pattern of synthesis and secretion in conjunction with the presence of the lectin in plasma indicate that it is a plasma protein of hepatocyte origin. The slow kinetics of secretion compared to other secretory proteins indicate an unusual mechanism for the segregation of the lectin from other secretory proteins and/or a different intracellular pathway for secretion.

12/01/2018 · What is the path a secretory protein follows from ..

N2 - A lectin, previously designated the Man/GlcNAc-specific lectin or mannan-binding protein, is found in rat liver and plasma. Analysis of the structural requirements for oligosaccharide binding indicated that the specificity of this lectin is directed primarily at the 'core' and peptide region of glycopeptides. We have examined synthesis and secretion of the core-specific lectin by primary rat hepatocytes and a rat hepatoma, H-4-II-E, utilizing pulse labeling with [35S]methionine, immunoprecipitation with a monospecific rabbit antibody raised against the purified lectin, and analysis by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and fluorography. A post-translational modification occurs between 10 and 40 min of chase which results in an increase in the M(r) from 24,000 to 26,000. This modification is not due to asparagine-linked glycosylation or oligosaccharide processing. The kinetics of secretion are unusual. Secretion begins at 1 h of chase and proceeds linearly for approximately 8 h until a maximum of 70% of the lectin has been secreted. Secretion, but not the post-translational modification is inhibited by monensin. The pattern of synthesis and secretion in conjunction with the presence of the lectin in plasma indicate that it is a plasma protein of hepatocyte origin. The slow kinetics of secretion compared to other secretory proteins indicate an unusual mechanism for the segregation of the lectin from other secretory proteins and/or a different intracellular pathway for secretion.

the path a secretory protein follows from synthesis to secretion

Basolateral-specific transport pathways are also thought to play key roles in polarized cells. The best studied of these pathways in is in the transport of the EGF-receptor in the vulval precursor cells (VPCs; see ). is normally restricted to the basolateral membrane of the VPCs, a process that requires the PDZ-domain proteins , , and (). The /7/10 complex binds directly to the intracellular domain, and is therefore likely to function as a sorting factor, directing to the basolateral membrane during secretion and/or after endocytosis and recycling (). The protein has been shown to associate with an intracellular compartment on or near the Golgi consistent with a role in protein sorting during secretion ().

AB - A lectin, previously designated the Man/GlcNAc-specific lectin or mannan-binding protein, is found in rat liver and plasma. Analysis of the structural requirements for oligosaccharide binding indicated that the specificity of this lectin is directed primarily at the 'core' and peptide region of glycopeptides. We have examined synthesis and secretion of the core-specific lectin by primary rat hepatocytes and a rat hepatoma, H-4-II-E, utilizing pulse labeling with [35S]methionine, immunoprecipitation with a monospecific rabbit antibody raised against the purified lectin, and analysis by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and fluorography. A post-translational modification occurs between 10 and 40 min of chase which results in an increase in the M(r) from 24,000 to 26,000. This modification is not due to asparagine-linked glycosylation or oligosaccharide processing. The kinetics of secretion are unusual. Secretion begins at 1 h of chase and proceeds linearly for approximately 8 h until a maximum of 70% of the lectin has been secreted. Secretion, but not the post-translational modification is inhibited by monensin. The pattern of synthesis and secretion in conjunction with the presence of the lectin in plasma indicate that it is a plasma protein of hepatocyte origin. The slow kinetics of secretion compared to other secretory proteins indicate an unusual mechanism for the segregation of the lectin from other secretory proteins and/or a different intracellular pathway for secretion.

What is the pathway of secretory proteins

Polarized cells such as epithelia maintain distinct apical and basolateral plasma membrane domains with distinct protein and lipid compositions. These specializations of the plasma membrane require complex membrane trafficking pathways thought to include unique basolateral versus apical sorting mechanisms in the secretory pathway to direct newly synthesized proteins to the correct membrane domain. Additional regulation of the endocytosis pathway maintains polarity of lipid and protein components after internalization and recycling.

The transcription of ribosomal DNA, ribosomal protein (RP) genes, and 5S and tRNA genes by RNA polymerases (Pols) I, II, and III, respectively, is rapidly and coordinately repressed upon interruption of the secretory pathway in Saccharomyces cerevisiae. We find that repression of ribosome and tRNA synthesis in secretion-defective cells involves activation of the cell integrity pathway. Transcriptional repression requires the upstream components of this pathway, including the Wsc family of putative plasma membrane sensors and protein kinase C (PKC), but not the downstream Bck1–Mkk1/2–Slt2 mitogen-activated protein kinase cascade. These findings reveal a novel PKC effector pathway that controls more than 85% of nuclear transcription. It is proposed that the coordination of ribosome and tRNA synthesis with cell growth may be achieved, in part, by monitoring the turgor pressure of the cell.

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is a secretory pathway protein.

Another class of proteins thought to function in secretion are those related to the putative hedgehog receptor Patched. Kuwabara and colleagues have identified 29 patched (PTC) or patched related (PTR) genes in the genome, each of which encodes a predicted multipass transmembrane protein with a predicted sterol-sensing domain (). The phenotypes of mutants indicate a likely defect in the secretory pathway and in germline cytokinesis in particular. The presence of such a large and diverse family of these proteins in could indicate diverse functions in membrane trafficking processes ().

Secretory Pathway | Secretion | Protein Targeting

In the past several years, studies with Saccharomyces cerevisiae have uncovered a regulatory circuit that connects the synthesis of the large rRNAs and RPs with the secretory pathway (, , ). These studies have shown that interruption of the secretory pathway at various points, from peptide insertion into the endoplasmic reticulum (ER) to vesicle fusion with the plasma membrane, causes transcriptional repression of ribosomal DNA (rDNA) and RP genes. The intracellular signaling pathway mediating this response does not involve any of the common mechanisms known to regulate ribosome biosynthesis and is distinct from the pathway that monitors protein folding in the ER (, ). However, continued protein synthesis and protein kinase C (PKC) are both required for repression in secretion-defective cells (, ). These findings, together with the fact that repression of RP genes can be induced by chlorpromazine, an agent that causes membrane stretching, provide the current working model for signal transduction in this system (). It is proposed that a failure of the secretory pathway leads to an insufficiency in the supply of lipids and proteins which are needed for growth of the plasma membrane and cell wall synthesis. In the absence of plasma membrane growth, continued protein synthesis is thought to create a higher-than-normal intracellular pressure (turgor), effectively stretching the plasma membrane. This perturbation of the plasma membrane is suggested to activate a PKC-dependent cell integrity pathway leading to transcriptional repression of ribosome synthesis. Activation of the PKC–mitogen-activated protein (MAP) kinase cell integrity pathway following an increase in the osmotic gradient across the plasma membrane (high inside, low outside) is well documented (). However, the role of this pathway in repressing rRNA and RP gene transcription in secretion-blocked cells has not yet been fully explored.

Secretory pathway, Plasmodium, Protein secretion

One component of the general secretory pathway that has been studied in significant detail in is , a part of the endoplasmic reticulum vesicle coat complex known as COPII (). COPII is known to be the primary vesicle coat complex used in yeast and mammalian cell transport from the ER to the Golgi. Roberts et al. identified a single mutant allele of in a screen for embryonic lethals defective in cuticle synthesis as assayed by a cuticle collagen reporter, (). These authors went on to show severe defects in cuticle synthesis in mutants resulting in accumulation of collagen intracellularly, presumably in the ER. Zygotic embryonic lethality during elongation was found in homozygous mutants derived from heterozygous mothers. Normal progression through early development presumably relies upon maternally derived . RNAi experiments revealed a requirement for during larval development, particularly during molting. Adults depleted of by RNAi also showed severe germline defects including binucleate oocytes, lack of yolk uptake by oocytes resulting from a failure of yolk receptors () to reach the cell surface, and premature maturation/partitioning of individual germ cells, possibly resulting from loss of cell surface receptors in the distal gonad. A partially functional ::GFP reporter gene indicated that is broadly expressed at all life stages, and that in hypodermal cells the protein is concentrated in distinct foci. In the embryonic hypodermis these foci were enriched apically at the periphery of the endoplasmic reticulum. These positive foci likely represent ER exit sites where newly synthesized cargo molecules concentrate and are packaged into COPII coated vesicles for delivery to the Golgi.

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