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Encyclopedia > Protein targeting

Protein targeting a.k.a. protein sorting includes the mechanisms by which a biological cell transports proteins to the appropriate organelle for insertion into a membrane or secretion to the outside. (This article deals with protein targeting in eukaryotes except as noted.) Cells in culture, stained for keratin (red) and DNA (green). ... A representation of the 3D structure of myoglobin, showing coloured alpha helices. ... Schematic of typical animal cell, showing subcellular components. ... A biological membrane or biomembrane is a membrane which acts as a barrier within or around a cell. ... Secretion is the process of segregating, elaborating, and releasing chemicals from a cell, or a secreted chemical substance or amount of substance. ... Kingdoms Animalia - Animals Fungi Plantae - Plants Protista A eukaryote is an organism with a complex cell or cells, in which the genetic material is organized into a membrane-bound nucleus or nuclei. ...

Contents


Protein translocation

In 1970, G√ľnter Blobel conducted experiments on the translocation of proteins across membranes. He was awarded the 1999 Nobel prize for his findings. He discovered that many proteins have a signal sequence, that is, a short amino acid sequence at one end that functions like a postal code for the target organelle. The translation of mRNA into protein by a ribosome takes place within the cytosol. If the synthesized proteins "belong" in a different organelle, they can be transported there in either of two ways, depending on the protein. 1970 (MCMLXX) was a common year starting on Thursday (the link is to a full 1970 calendar). ... Günter Blobel (born May 21, 1936) is a German biologist. ... 1999 (MCMXCIX) was a common year starting on Friday, and was designated the International Year of Older Persons by the United Nations. ... List of Nobel Prize laureates in Physiology or Medicine from 1901 to the present day. ... A signal peptide is a short (15-60 amino acids long) peptide chain that directs the post transrational transport of a protein. ... An amino acid residue is what is left of an amino acid once a molecule of water has been lost (an H+ from the nitrogenous side and an OH- from the carboxylic side) in the formation of a peptide bond. ... A postal code (known in various countries as a post code, postcode, or ZIP code) is a series of letters and/or digits appended to a postal address for the purpose of sorting mail. ... Translation in the cytoplasm; tRNA carries amino acids which are added to the growing peptide chain in the ribosome. ... The interaction of mRNA in a eukaryote cell. ... Figure 1: Ribosome structure indicating small subunit (A) and large subunit (B). ... ÃThe cytosol (as opposed fatty cytoplasm, which also includes the organelles) is the internal fluid of the cell, and a large part of cell metabolism occurs here. ...


Cotranslational translocation

The N-terminal signal sequence of the protein is recognized by a signal recognition particle (SRP) while the protein is still being synthesized on the ribosome. The synthesis pauses while the ribosome-protein complex is transferred to an SRP receptor on the endoplasmic reticulum (ER, which is a membrane-bound organelle). There, the nascent protein is inserted into the Sec61 translocation complex (also known as the translocon) that passes through the ER membrane. The signal sequence is immediately cleaved from the polypeptide once it has been translocated into the ER by signal peptidase in secretory proteins. This signal sequence processing differs for some ER transmembrane proteins. Within the ER, the protein is first covered by a chaperone protein to protect it from the high concentration of other proteins in the ER, giving it time to fold correctly. Once folded, the protein is modified as needed (for example, by glycosylation), then transported to the Golgi apparatus for further processing and goes to its target organelles or is retained in the ER by various ER retention mechanisms. The signal recognition particle (SRP) is a protein-RNA complex that recognizes and transports specific proteins to the endoplasmic reticulum in eukaryotes and the plasma membrane in prokaryotes. ... The endoplasmic reticulum or ER (endoplasmic means within the cytoplasm, reticulum means little net) is an organelle found in all eukaryotic cells. ... A transmembrane protein is an integral membrane protein that spans from the internal to the external surface of the biological membrane or lipid bilayer in which it is embedded. ... In biology, chaperones are proteins whose function is to assist other proteins in achieving proper folding. ... Protein folding is the process by which a protein structure assumes its functional shape or conformation. ... Glycosylation is the process or result of addition of saccharides to proteins and lipids. ... In cell biology, the Golgi apparatus (also called a Golgi body, Golgi complex, or dictyosome) is an organelle found in most eukaryotic cells, including those of plants, animals, and fungi. ... Proteins that are retained in the Endoplasmic Reticulum, or ER, after folding are known as ER resident proteins. ...


Posttranslational translocation

Even though most proteins are cotranslationally translocated, some are translated in the cytosol and later transported to their destination. This occurs for proteins that go to a mitochondrion, a chloroplast, or a peroxisome (proteins that go to the latter have their signal sequence at the C terminus). Also, proteins targeted for the nucleus are translocated post-translation. They pass through the nuclear envelope via nuclear pores. ÃThe cytosol (as opposed fatty cytoplasm, which also includes the organelles) is the internal fluid of the cell, and a large part of cell metabolism occurs here. ... electron micrograph of a mitochondrion showing its mitochondrial matrix and membranes In cell biology, a mitochondrion (plural mitochondria) (from Greek mitos thread + khondrion granule) is an organelle, variants of which are found in most eukaryotic cells. ... The inside of a chloroplast Chloroplasts are organelles found in plant cells and eukaryotic algae that conduct photosynthesis. ... Basic structure of a peroxisome Peroxisomes are ubiquitous organelles in eukaryotes that function to rid the cell of toxic substances. ... In cell biology, the nucleus (from Latin nucleus or nuculeus, kernel) is found in all eukaryotic cells and contains the nuclear genes which form most of the cells genetic material. ... The nuclear envelope refers to the double membrane of the nucleus that encloses genetic material in eukaryotic cells. ... Nuclear pore. ...


Transmembrane proteins

The amino acid chain of transmembrane proteins, which often are transmembrane receptors, passes through a membrane one or several times. They are inserted into the membrane by translocation, until the process is interrupted by a stop-transfer sequence, also called a membrane anchor sequence. NIGGGGGGGGAAAAAAAAAAAAAAAA PLEASE A transmembrane protein is an integral membrane protein that spans from the internal to the external surface of the biological membrane or lipid bilayer in which it is embedded. ... Transmembrane receptors are integral membrane proteins, which reside and operate typically within a cells plasma membrane, but also in the membranes of some subcellular compartments and organelles. ...


Sorting of proteins to mitochondria

Most mitochondrial proteins are synthesized as cytosolic precursors containing uptake peptide signals. electron micrograph of a mitochondrion showing its mitochondrial matrix and membranes In cell biology, a mitochondrion (plural mitochondria) (from Greek mitos thread + khondrion granule) is an organelle, variants of which are found in most eukaryotic cells. ... A signal peptide is a short (15-60 amino acids long) peptide chain that directs the post translational transport of a protein. ...


Mitochondrial matrix targeting sequences are rich in positively charged amino acids and hydroxylated ones. In biology, the word matrix is used for the material between animal or plant cells, or generally the material (or tissue) in which more specialized structures are embedded, and also specifically for one part of the mitochondrion. ...


Proteins are targeted to submitochondrial compartments by multiple signals and several pathways.


Targeting to the outer membrane, intermembrane space, and inner membrane often requires another signal sequence in addition to the matrix targeting sequence. The intermembrane space is the region between the inner membrane and the outer membrane of a mitochondrion or a chloroplast. ...


Cytosolic chaperones deliver proteins to channel linked receptors in the mitochondrial membrane. In cell biology, a mitochondrion is an organelle found in the cells of most eukaryotes. ...


Sorting of proteins to peroxisomes

All peroxisomal proteins are encoded by nuclear genes. Basic structure of a peroxisome Peroxisomes are ubiquitous organelles in eukaryotes that function to rid the cell of toxic substances. ...


The signal for uptake into the peroxisomal matrix is SKL (serine-lysine-leucine). SKL can stand for: Suomen Kristillinen Liitto (Finnish Christian League) Süddeutsche Klassenlotterie (a German lottery) Seekriegsleitung or Naval Warfare Command, which led the German Navy during the First World War. ... Serine is one of the 20 natural amino acids. ... Lysine is one of the 20 amino acids normally found in proteins. ... Leucine is one of the 20 most common amino acids and coded for by DNA. It is isomeric with isoleucine. ...


Diseases

Peroxisomal protein transport is defective in the following genetic diseases:

Zellweger syndrome is a rare, congenital disorder (present at birth), characterized by the reduction or absence of peroxisomes (cell structures that rid the body of toxic substances) in the cells of the liver, kidneys, and brain. ... Adrenoleukodystrophy (ALD) is a degenerative disorder of the fatty white sheath covering nerve fibers, known as myelin. ...

Receptor-mediated endocytosis

Several molecules that attach to special receptors called coated pits on the outside of cells cause the cell to perform endocytosis, an invagination of the plasma membrane to incorporate the molecule and associated structures into endosomes. This mechanism is used for three main purposes: Endocytosis is a process whereby cells absorb material (molecules such as proteins) from outside by engulfing it with their cell membrane. ... Drawing of a cell membrane A component of every biological cell, the cell membrane (or plasma membrane) is a thin and structured bilayer of phospholipid and protein molecules that envelopes the cell. ... In biology an endosome is an endocytotic vesicle derived from the plasma membrane. ...

Receptor-mediated endocytosis can also be "abused": Low-density lipoprotein (LDL) refers to a class and range of lipoprotein particles, varying somewhat in their size and contents, which carry cholesterol in the blood and around the body, for use by various cells. ... A hormone (from Greek horman - to set in motion) is a chemical messenger from one cell (or group of cells) to another. ... Growth factor is a protein that acts as a signaling molecule between cells (like cytokines and hormones) that attaches to specific receptors on the surface of a target cell and promotes differentiation and maturation of these cells. ... Epidermal Growth Factor or EGF is a 6045 Da protein with 53 amino acid residues and three intramolecular disulfide bonds. ... Nerve growth factor (NGF), the prototypical growth factor, is a protein secreted by a neurons target. ... An antigen is a substance that stimulates an immune response, especially the production of antibodies. ... Phagocytosis (literally cell-eating) is a form of endocytosis wherein large particles are enveloped by the cell membrane of a (usually larger) cell and internalized to form a phagosome, or food vacuole. ... A macrophage of a mouse stretching its arms to engulf two particles, possibly pathogens Macrophages (Greek: big eaters, makros = long, phagein = eat) are white blood cells, more specifically phagocytes, acting in the nonspecific defense as well as the specific defense system of vertebrate animals. ...

A common alternate meaning of virus is computer virus. ... The Semliki Forest Virus was first isolated from mosquitoes in the Semliki Forest, Uganda by the Uganda Virus Research Institute in 1944. ... Drawing of Death bringing the cholera, in Le Petit Journal. ...

Protein destruction

Defective proteins are occasionally produced, or they may be damaged later, for example, by oxidative stress. Damaged proteins can be recycled. Proteins can have very different half lives, mainly depending on their N-terminal amino acid residue. The recycling mechanism is mediated by ubiquitin. The most fundamental reactions in chemistry are the redox processes. ... Half-Life is a science fiction first-person shooter computer game developed by Valve Software and published by Sierra Studios in 1998, based on a heavily-modified Quake game engine. ... // Background Ubiquitylation, also termed ubiquitination, refers to the process particular to eukaryotes whereby a protein is post-translationally modified by covalent attachment of a small protein. ...


Protein targeting in bacteria

Bacteria do not have organelles they can send proteins to, but some proteins are incorporated into the plasma membrane or secreted into the environment. The basic mechanism is similar to the eukaryotic one. Phyla/Divisions Actinobacteria Aquificae Bacteroidetes/Chlorobi Chlamydiae/Verrucomicrobia Chloroflexi Chrysiogenetes Cyanobacteria Deferribacteres Deinococcus-Thermus Dictyoglomi Fibrobacteres/Acidobacteria Firmicutes Fusobacteria Gemmatimonadetes Nitrospirae Omnibacteria Planctomycetes Proteobacteria Spirochaetes Thermodesulfobacteria Thermomicrobia Thermotogae Bacteria (singular, bacterium) are a major group of living organisms. ...


Secretory pathways

The secretory pathway includes vesicular traffic, secretion, and endocytosis. Secretory proteins follow this pathway. A secretory pathway is a term used to describe different methods that cells use to transport material to the outside, usually from the endoplasmic reticulum via the Golgi apparatus. ... A secretory protein is any protein, whether it be endocrine or exocrine, which is secreted by a cell. ...


Early stages

Retrograde transport is common in the early stages. Proteins that have been successfully delivered to the Golgi apparatus advance through cisternal progression. In cell biology, the Golgi apparatus (also called a Golgi body, Golgi complex, or dictyosome) is an organelle found in most eukaryotic cells, including those of plants, animals, and fungi. ... This article is confusing for some readers, and needs to be edited for clarity. ...


Later stages

Coated vesicles mediate several transport steps.



Proteins

Protein biosynthesis | Posttranslational modification | Protein folding | Protein structure | Protein structural domains | Protein targeting | Proteasome | List of proteins | Membrane protein | Globular protein | Fibrous protein | List of types of proteins | Proteome | Protein methods A representation of the 3D structure of myoglobin, showing coloured alpha helices. ... An overview of protein synthesis. ... Posttranslational modification means the chemical modification of a protein after its translation. ... Protein folding is the process by which a protein structure assumes its functional shape or conformation. ... Proteins are amino acid chains, made up from 20 different L-α-amino acids, also referred to as residues, that fold into unique three-dimensional protein structures. ... Within a protein, a structural domain (domain) is an element of overall structure that is self-stabilizing and often folds independently of the rest of the protein chain. ... A proteasome is a barrel-shaped multi-protein complex that can digest other proteins into short polypeptides and amino acids in an ATP-driven reaction. ... A list of proteins (and protein complexes). ... A membrane protein is a protein molecule that is attached to, or associated with the membrane of a cell or an organelle. ... Globular proteins, or spheroproteins are one of the two main protein classes, comprising globelike proteins that are more or less soluble in aqueous solutions (where they form colloidal solutions). ... Fibrous proteins, also called scleroproteins, are long filamentous protein molecules that form one of the two main classes of tertiary structure protein (the other being globular proteins). ... Wikipedia is in the process of constructing a description of all major protein types and all important individual proteins. ... The term proteome was coined by Mark Wilkins in 1995 (1) and is used to describe the entire complement of proteins in a given biological organism or system at a given time, i. ... Protein methods are the techniques used to study proteins. ...


  Results from FactBites:
 
Protein - Wikipedia, the free encyclopedia (3139 words)
Proteins are essential to the structure and function of all living cells and viruses.
Proteins are generally large molecules, having molecular masses of up to 3,000,000 (the muscle protein titin has a single amino acid chain 27,000 subunits long) however protein masses are generally measured in kiloDaltons (kDa).
Proteins are broken down by proteases into smaller polypeptides to provide amino acids for the organism, including those the organism may not be able to synthesize itself.
  More results at FactBites »

 
 

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