Secretion and processing modification after protein synthesis.

. NetworkSection III
Protein
After synthesis of secretion and processing modification whether primary or endogenetic organisms, proteins synthesized in the plasma need to be located in cell-specific areas, some proteins synthesized to secrete outside the cell, these proteins are called sub-proteins. Proteins that work in bacterial cells are generally distributed to their destinations by diffusion. For example, the inner membrane contains proteins involved in energy metabolism and nutrient transport, the outer membrane contains proteins that promote the entry of ions and nutrients into the cells, and the gap between the inner and outer membranes is called peritonum, which contains various hydrolyzed enzymes and nutrient binding proteins.The uclear biocellular structure is more complex, and there are many different cellular devices, they have different membrane structures, so synthetic proteins also have to face across different membranes to reach the cell device, some proteins after translation also have to go through a variety of co-price modification, this process is called post-translation processing.(i) How do the transfilmcell endoin proteins, outer membrane proteins, and peritonal proteins of proteins in bacteria cross the endometrium to their destination? The N-side of the vast majority of transfilm proteins has approximately 15-30 N-side signal sequences, or signal peptides, dominated by hydrophobic
amino acids
. The hydrophobic segment of the signal peptide can form a α spiral structure. After the signal sequence, an amino acid residue can also form a α helix, two α helix in an anti-parallel way to form a hairpin structure, it is easy to enter the lipid double layer structure of the inner membrane, once the N-end of the secretion protein anchored in the membrane, the subsequent synthesis of other peptide segments will pass through the membrane smoothly. Hydrophobic signal peptides act as an inflection on the transfilm of the new peptide chain and on the membrane on which it is fixed. The signal peptide sequence is then removed by the signal peptide enzyme located on the outer surface of the inner membrane. When all the proteins are translated, the ends pass through the inner membrane and fold into the final composition of the protein in the peritonal mass (Figures 18-18).. Figure 18-18 The secretion process after protein synthesis(ii) the secretion of the epineural bioproteinthe endogenous organism not only has the nuclei, cytostyles and cell membranes, but also has many membrane structure organels, how does the protein synthesized within the cell reach different parts of the cell? What is clearer is the transport of secretive proteins.Is like primary nucleocytes, the protein N-side synthesized by the epidural also has signal peptides that can also form two α-helix hairpin structures that can be inserted into the membrane of the endoscopic mesh, which will be synthesized into the
peptide
chain band and endotrogen mesh inner cavity. In the mid-1980s, a complex of small molecule RNA and proteins was found in the plasma, which can be specifically identified with signal peptides and named signal peptide recognition particles. Its role is to identify the binding of signal peptides to ucose and temporarily block the synthesis of peptide chains. SRP subject on endotral mesh membrane, when ARP and the subject binding, signal peptides can be inserted into the endotrogen mesh into the inner cavity, by the endotide mesh wall signal peptide enzyme water to remove SRP and the subject binding, signal peptides can be inserted into the endoscopic network into The inner cavity, which is dissociate from the subject and enters a new cycle by the signal peptide enzyme water on the inner cavity wall of the endoscopic mesh, also enters the inner cavity of the internal network and begins to synthesize the peptide chain (Figures 18-19).. Figure 18-19 The role of SRP and shipyard proteins (or SRP subjects) in the transport of proteins across endoblasts SRP's important physiological significance for the translation phase is that the membrane cells that secrete proteins enter cells early, fold correctly, perform the necessary post-processing and modification, and successfully secrete cells.is now using mammalian insulin as an example to illustrate this secretion process. Insulin consists of 51 amino acid residues, but the translation of insulin mRNA and 86 amino acid residues in the rabbit mesh erythocyte cellless translation system, called insulinogen, in the wheat embryo cellless translation system for 110 amino acid residues The pre-insulin original of the base composition, it was later proved that at the N end of the ex-insulin original, there is a peptide segment rich in hydrophobic amino acids as a signal peptide, so that the pre-insulin original can pass through the endocyclic mesh into the inner mesh cavity, the signaling peptide on the inner cavity wall is water-mediated. So in mammalian cells, when the synthesis of peptide chains is complete, pre-insulin has become insulinogen. The insulin is then transported to the Gorki complex, where the C peptide is cut into mature insulin, which is eventually excreted. There are similar ways to split, such as pre-clear proteins in the nucleocytes, immune globulin white chains, oxytocin, etc.(iii) Protein translation processing modificationfrom the nuclear glycogen released polypeptide chain, according to the nature of the amino acid side chain in the first structure, since bamboo curling, the formation of a certain spatial structure, in the past has been believed that the formation of the protein spatial structure is determined by its first-level structure, do not need additional information. In recent years, it has been found that the correct assembly of many in-cell proteins requires the help of a class of proteins called "bridesmaids", and the concept does not negate the principle that amino acid sequentiality determines the spatial structure of proteins. Instead, this theory is supplemented by the fact that proteins such as molecular bridesmaids can mediate other proteins into functionally active spatial structures that are not themselves involved in the composition of the final assembly product. It is currently believed that there are two types of "molecular bridesmaid" proteins, the first is some enzymes, such as protein disulfur bond isomerase can identify and hydrolyzed non-correctly paired disulfur bonds, so that they re-form the disulfur bonds in the correct cysteine residue position, the second category is some protein molecules, they can be partially folded or not folded protein molecules binding, stabilize their composition, from other enzymes hydrolyzed or promote protein folding into the correct spatial structure. In short, "molecular bridesmaids" protein synthesis after folding into the correct spatial structure plays an important role, for most proteins polypeptide chain translation after the following different ways of processing modification to have physiological functions.. 1. Modification of the amino and carboxyl endsAlmost all proteins in primary nuclear organisms start with N-methyl methionine, and the endural organisms start with methionine. Methyl is removed by enzyme water, and some amino acid residues at methionine or amino ends are often catalyzed by amino enzymes and removed by water. Includes the removal of the signal peptide sequence. Therefore, the mature protein molecule N-end has no methyl, or no methionine. At the same time, some protein molecular amino ends to be acetylized in the base end of the carboxyme also need to be modified.. 2. Co-price modificationMany proteins can be modified with different types of chemical groups, after modification can be shown as active state, can also be shown as inactivated state. (1)
phosphate
: Phosphate occurs mostly on polypeptide stresine, hydroxyl suline, and occasionally on tyrosine residues, a phosphate process affected by a protein in the cell
kinase
catalysis, phosphate proteins can increase or decrease their activity, for example: promote the decomposition of glycogen phosphatase, inactive phosphatase b after phosphate, become active phosphatasea. The active glycogen synthase I is phosphatized and becomes the inactive glycogen synthase D, which jointly regulates the synthesis and distribution of glycogens. (2) Glycosylation: -quality membrane proteins and many secretive proteins have sugar chains that bind to hydroxyl serine or suline, such as ABO blood type-determining clusters on red blood cell membranes. It can also be connected to Tianmen dongamide. These oligosaccharine chains are added to the endosome or goerkis (Figures 18-20). . Figure 18-20 Glycotin commonly found in glycopeptide connection bonds (3) hydroxylation: proline and lysine residues in the collagen pre-α chain are affected by hydroxyase, molecular oxygen and
vitamin
C to produce hydroxy proline and lysine, if this process is affected by collagen fiber can not be cross-linked, greatly reducing its stress strength. (4) Formation of the two sulfur bonds: mRNA does not have cysteine codex, the polypeptide chain of the two sulfur bonds, is formed after the peptide chain synthesis, through the two cysteine dredging oxidation, the formation of the two sulfur bonds for many enzymes and protein activity is necessary. . 3. Aggregation of sub-base: many proteins are composed of more than two sub-base, which requires these peptide chains to be polymerized into polymers through non-co-priced bonds in order to express biological activity. For example, adult hemoglobin consists of two α chains, two β chains and four molecules of hemoglobin, the general process is as follows: the α chain is self-released after the synthesis of polyurucleosomes, and has not yet been released from the polyurucleucleosome β chain, and then removed from the polyucleucleosome, into α, β hydrome. The djust binds to two hemoglobins produced in the mitochondrials, resulting in a functional hemoglobin molecule consisting of four peptide chains and four hemoglobins. . 4. Water-mediated broken chain: A
gene in a common urn
corresponds to an mRNA, an mRNA corresponds to a peptide chain, but there are a few cases, that is, a three-think-how translation of the peptide chain after water to produce several different proteins or peptides. For example, the original translation product of the opiate-like black skin-promoting black skin
hormone
in mammals was 265 amino acids, which in the pituitary frontal leaf cells, poMC was initially cut into N-end fragments and C-end fragments of β-lipid-promoting hormone. The N-side fragments are then cut into smaller N-end fragments and adrenal-promoting corticosteroids of the 9 peptides. In the mid-leaf cells of the pituitary glyoph, β-lipid-promoting hormones are cut again to produce β-endorphins, and ACTH is cut to produce 13 peptides of black-promoting hormones (α-melanotropin) (Figures 18-21). . Figure 18-21 POMC is a prelude to a variety of active substances
the first behavior POMC prescultor, K, R is lysine and arginine residue




.