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Protein targeting or protein sorting is the biological mechanism by which proteins are transported to their appropriate destinations within or outside the cell. Proteins can be targeted to the inner space of an organelle, different intracellular membranes, the plasma membrane, or to the exterior of the cell via secretion. Information contained in the protein itself directs this delivery process. Correct sorting is crucial for the cell; errors or dysfunction in sorting have been linked to multiple diseases.
Thylakoids are membrane-bound compartments inside chloroplasts and cyanobacteria. They are the site of the light-dependent reactions of photosynthesis. Thylakoids consist of a thylakoid membrane surrounding a thylakoid lumen. Chloroplast thylakoids frequently form stacks of disks referred to as grana. Grana are connected by intergranal or stromal thylakoids, which join granum stacks together as a single functional compartment.
Secretion is the movement of material from one point to another, such as a secreted chemical substance from a cell or gland. In contrast, excretion is the removal of certain substances or waste products from a cell or organism. The classical mechanism of cell secretion is via secretory portals at the plasma membrane called porosomes. Porosomes are permanent cup-shaped lipoprotein structures embedded in the cell membrane, where secretory vesicles transiently dock and fuse to release intra-vesicular contents from the cell.
The periplasm is a concentrated gel-like matrix in the space between the inner cytoplasmic membrane and the bacterial outer membrane called the periplasmic space in Gram-negative bacteria. Using cryo-electron microscopy it has been found that a much smaller periplasmic space is also present in Gram-positive bacteria, between cell wall and the plasma membrane. The periplasm may constitute up to 40% of the total cell volume of gram-negative bacteria, but is a much smaller percentage in gram-positive bacteria.
Moraxella catarrhalis is a fastidious, nonmotile, Gram-negative, aerobic, oxidase-positive diplococcus that can cause infections of the respiratory system, middle ear, eye, central nervous system, and joints of humans. It causes the infection of the host cell by sticking to the host cell using trimeric autotransporter adhesins.
Adhesins are cell-surface components or appendages of bacteria that facilitate adhesion or adherence to other cells or to surfaces, usually in the host they are infecting or living in. Adhesins are a type of virulence factor.
The bacterial outer membrane is found in gram-negative bacteria. Gram-negative bacteria form two lipid bilayers in their cell envelopes - an inner membrane (IM) that encapsulates the cytoplasm, and an outer membrane (OM) that encapsulates the periplasm.
Filamentation is the anomalous growth of certain bacteria, such as Escherichia coli, in which cells continue to elongate but do not divide. The cells that result from elongation without division have multiple chromosomal copies.
In molecular biology, the Signal Peptide Peptidase (SPP) is a type of protein that specifically cleaves parts of other proteins. It is an intramembrane aspartyl protease with the conserved active site motifs 'YD' and 'GxGD' in adjacent transmembrane domains (TMDs). Its sequences is highly conserved in different vertebrate species. SPP cleaves remnant signal peptides left behind in membrane by the action of signal peptidase and also plays key roles in immune surveillance and the maturation of certain viral proteins.
Maltose-binding protein (MBP) is a part of the maltose/maltodextrin system of Escherichia coli, which is responsible for the uptake and efficient catabolism of maltodextrins. It is a complex regulatory and transport system involving many proteins and protein complexes. MBP has an approximate molecular mass of 42.5 kilodaltons.
Translocase is a general term for a protein that assists in moving another molecule, usually across a cell membrane. These enzymes catalyze the movement of ions or molecules across membranes or their separation within membranes. The reaction is designated as a transfer from “side 1” to “side 2” because the designations “in” and “out”, which had previously been used, can be ambiguous. Translocases are the most common secretion system in Gram positive bacteria.
In biology, an autoinducer is a signaling molecule that enables detection and response to changes in the population density of bacterial cells. Synthesized when a bacterium reproduces, autoinducers pass outside the bacterium and into the surrounding medium. They are a key component of the phenomenon of quorum sensing: as the density of quorum-sensing bacterial cells increases, so does the concentration of the autoinducer. A bacterium’s detection of an autoinducer above some minimum threshold triggers altered gene expression.
The SecY protein is the main transmembrane subunit of the bacterial Sec export pathway and of a protein-secreting ATPase complex, also known as a SecYEG translocon. Homologs of the SecYEG complex are found in eukaryotes and in archaea, where the subunit is known as Sec61α.
ATP-dependent Clp protease proteolytic subunit (ClpP) is an enzyme that in humans is encoded by the CLPP gene. This protein is an essential component to form the protein complex of Clp protease.
In molecular biology, the FHIPEP protein family consists of a number of proteins that constitute the type III secretion pathway apparatus. This mechanism translocates proteins lacking an N-terminal signal peptide across the cell membrane in one step, as it does not require an intermediate periplasmic process to cleave the signal peptide. It is a common pathway amongst Gram-negative bacteria for secreting toxic and flagellar proteins.
Membrane vesicle trafficking in eukaryotic animal cells involves movement of biochemical signal molecules from synthesis-and-packaging locations in the Golgi body to specific release locations on the inside of the plasma membrane of the secretory cell. It takes place in the form of Golgi membrane-bound micro-sized vesicles, termed membrane vesicles (MVs).
The TIC and TOC complexes are translocons located in the chloroplast of a eukaryotic cell, that is, protein complexes that facilitate the transfer of proteins in and out through the chloroplast's membrane. It mainly transports proteins made in the cytoplasm into the chloroplast. The TIC complex(translocon on the inner chloroplast membrane) is located in the inner envelope of the chloroplast. The TOC complex(translocon on the outer chloroplast membrane) is located in the outer envelope of the chloroplast.
Resistance-nodulation-division (RND) family transporters are a category of bacterial efflux pumps, especially identified in Gram-negative bacteria and located in the cytoplasmic membrane, that actively transport substrates. The RND superfamily includes seven families: the heavy metal efflux (HME), the hydrophobe/amphiphile efflux-1, the nodulation factor exporter family (NFE), the SecDF protein-secretion accessory protein family, the hydrophobe/amphiphile efflux-2 family, the eukaryotic sterol homeostasis family, and the hydrophobe/amphiphile efflux-3 family. These RND systems are involved in maintaining homeostasis of the cell, removal of toxic compounds, and export of virulence determinants. They have a broad substrate spectrum and can lead to the diminished activity of unrelated drug classes if over-expressed. The first reports of drug resistant bacterial infections were reported in the 1940s after the first mass production of antibiotics. Most of the RND superfamily transport systems are made of large polypeptide chains. RND proteins exist primarily in gram-negative bacteria but can also be found in gram-positive bacteria, archaea, and eukaryotes.
Bacterial secretion systems are protein complexes present on the cell membranes of bacteria for secretion of substances. Specifically, they are the cellular devices used by pathogenic bacteria to secrete their virulence factors to invade the host cells. They can be classified into different types based on their specific structure, composition and activity. Generally, proteins can be secreted through two different processes. One process is a one-step mechanism in which proteins from the cytoplasm of bacteria are transported and delivered directly through the cell membrane into the host cell. Another involves a two-step activity in which the proteins are first transported out of the inner cell membrane, then deposited in the periplasm, and finally through the outer cell membrane into the host cell.
The Phosphate (Pho) regulon is a regulatory mechanism used for the conservation and management of inorganic phosphate within the cell. It was first discovered in Escherichia coli as an operating system for the bacterial strain, and was later identified in other species. The Pho system is composed of various components including extracellular enzymes and transporters that are capable of phosphate assimilation in addition to extracting inorganic phosphate from organic sources. This is an essential process since phosphate plays an important role in cellular membranes, genetic expression, and metabolism within the cell. Under low nutrient availability, the Pho regulon helps the cell survive and thrive despite a depletion of phosphate within the environment. When this occurs, phosphate starvation-inducible (psi) genes activate other proteins that aid in the transport of inorganic phosphate.
References
- ↑ Sargent, F.; Berks, B.C.; Palmer, T. (2006). "Pathfinders and trailblazers: a prokaryotic targeting system for transport of folded proteins". FEMS Microbiol. Lett. 254 (2): 198–207. doi: 10.1111/j.1574-6968.2005.00049.x . PMID 16445746.
- ↑ Carrie, Chris; Weißenberger, Stefan; Soll, Jürgen (2016-10-15). "Plant mitochondria contain the protein translocase subunits TatB and TatC". Journal of Cell Science. 129 (20): 3935–3947. doi: 10.1242/jcs.190975 . ISSN 0021-9533. PMID 27609835.
- ↑ Bennewitz, Bationa; Sharma, Mayank; Tannert, Franzisca; Klösgen, Ralf Bernd (November 2020). "Dual targeting of TatA points to a chloroplast-like Tat pathway in plant mitochondria". Biochimica et Biophysica Acta (BBA) - Molecular Cell Research. 1867 (11): 118816. doi: 10.1016/j.bbamcr.2020.118816 . PMID 32768405. S2CID 224889980.
- ↑ Barnett JP, Eijlander RT, Kuipers OP, Robinson C (2008). "A minimal Tat system from a gram-positive organism: a bifunctional TatA subunit participates in discrete TatAC and TatA complexes". J. Biol. Chem. 283 (5): 2534–2542. doi: 10.1074/jbc.M708134200 . PMID 18029357.
- ↑ Chaddock, A.M.; Mant, A.; Karnauchov, I.; Brink, S.; Herrmann, R.G.; Klösgen, R.B.; Robinson, C. (1995). "A new type of signal peptide: central role of a twin-arginine motif in transfer signals for the delta pH-dependent thylakoidal protein translocase". EMBO J. 14 (12): 2715–2722. doi:10.1002/j.1460-2075.1995.tb07272.x. PMC 398390 . PMID 7796800.
- ↑ Frielingsdorf, S.; Klösgen, R.B. (2007). "Prerequisites for Terminal Processing of Thylakoidal Tat Substrates". J. Biol. Chem. 282 (33): 24455–24462. doi: 10.1074/jbc.M702630200 . PMID 17581816.
- ↑ Sargent F, Bogsch EG, Stanley NR, Wexler M, Robinson C, Berks BC, Palmer T (1998). "Overlapping functions of components of a bacterial Sec-independent protein export pathway". EMBO Journal. 17 (13): 3640–50. doi:10.1093/emboj/17.13.3640. PMC 1170700 . PMID 9649434.
- ↑ Gouffi K, Santini CL, Wu LF (August 2002). "Topology determination and functional analysis of the Escherichia coli TatC protein". FEBS Lett. 525 (1–3): 65–70. Bibcode:2002FEBSL.525...65G. doi:10.1016/s0014-5793(02)03069-7. PMID 12163163.
- ↑ Organism