A transmembrane protein is a type of integral membrane protein that spans the entirety of the cell membrane. Many transmembrane proteins function as gateways to permit the transport of specific substances across the membrane. They frequently undergo significant conformational changes to move a substance through the membrane. They are usually highly hydrophobic and aggregate and precipitate in water. They require detergents or nonpolar solvents for extraction, although some of them (beta-barrels) can be also extracted using denaturing agents.
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 cell envelope comprises the inner cell membrane and the cell wall of a bacterium. In gram-negative bacteria an outer membrane is also included. This envelope is not present in the Mollicutes where the cell wall is absent.
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.
The Transporter Classification Database is an International Union of Biochemistry and Molecular Biology (IUBMB)-approved classification system for membrane transport proteins, including ion channels.
In protein structures, a beta barrel is a beta sheet composed of tandem repeats that twists and coils to form a closed toroidal structure in which the first strand is bonded to the last strand. Beta-strands in many beta-barrels are arranged in an antiparallel fashion. Beta barrel structures are named for resemblance to the barrels used to contain liquids. Most of them are water-soluble proteins and frequently bind hydrophobic ligands in the barrel center, as in lipocalins. Others span cell membranes and are commonly found in porins. Porin-like barrel structures are encoded by as many as 2–3% of the genes in Gram-negative bacteria. It has been shown that more than 600 proteins with various function contain the beta barrel structure.
Mitochondrial membrane transport proteins, also known as mitochondrial carrier proteins, are proteins which exist in the membranes of mitochondria. They serve to transport molecules and other factors, such as ions, into or out of the organelles. Mitochondria contain both an inner and outer membrane, separated by the inter-membrane space, or inner boundary membrane. The outer membrane is porous, whereas the inner membrane restricts the movement of all molecules. The two membranes also vary in membrane potential and pH. These factors play a role in the function of mitochondrial membrane transport proteins. There are 53 discovered human mitochondrial membrane transporters, with many others that are known to still need discovered.
Voltage-dependent anion channels, or mitochondrial porins, are a class of porin ion channel located on the outer mitochondrial membrane. There is debate as to whether or not this channel is expressed in the cell surface membrane.
General bacterial porins are a family of porin proteins from the outer membranes of Gram-negative bacteria. The porins act as molecular filters for hydrophilic compounds. They are responsible for the 'molecular sieve' properties of the outer membrane. Porins form large water-filled channels which allow the diffusion of hydrophilic molecules into the periplasmic space. Some porins form general diffusion channels that allow any solute up to a certain size to cross the membrane, while other porins are specific for one particular solute and contain a binding site for that solute inside the pores. As porins are the major outer membrane proteins, they also serve as receptor sites for the binding of phages and bacteriocins.
Outer membrane receptors, also known as TonB-dependent receptors, are a family of beta barrel proteins named for their localization in the outer membrane of gram-negative bacteria. TonB complexes sense signals from the outside of bacterial cells and transmit them into the cytoplasm, leading to transcriptional activation of target genes. TonB-dependent receptors in gram-negative bacteria are associated with the uptake and transport of large substrates such as iron siderophore complexes and vitamin B12.
Maltoporins are bacterial outer membrane proteins of the porin family. Maltoporin forms a trimeric structure which facilitates the diffusion of maltodextrins across the outer membrane of Gram-negative bacteria. The membrane channel is formed by an antiparallel beta-barrel.
Virulence-related outer membrane proteins, or outer surface proteins (Osp) in some contexts, are expressed in the outer membrane of gram-negative bacteria and are essential to bacterial survival within macrophages and for eukaryotic cell invasion.
Mycobacterial porins are a group of transmembrane beta-barrel proteins produced by mycobacteria, which allow hydrophilic nutrients to enter the bacterium. They are located in the impermeable mycobacterial outer membrane, or mycomembrane of fast-growing mycobacteria. The mycomembrane is unique and composed of very-long chain fatty acids, mycolic acids. These proteins are structurally different from the typical porins located in the outer membrane of Gram-negative bacteria. For example, the MspA protein forms a tightly interconnected octamer with eight-fold rotation symmetry that resembles a goblet and contains a central channel. Each protein subunit contains a beta-sandwich of immunoglobulin-like topology and a beta-ribbon arm that forms an oligomeric transmembrane beta-barrel.
Outer membrane protein G (OmpG) is a porin, a channel proteins in the outer membrane of Gram-negative bacteria.
Voltage-dependent anion-selective channel 1 (VDAC-1) is a beta barrel protein that in humans is encoded by the VDAC1 gene located on chromosome 5. It forms an ion channel in the outer mitochondrial membrane (OMM) and also the outer cell membrane. In the OMM, it allows ATP to diffuse out of the mitochondria into the cytoplasm. In the cell membrane, it is involved in volume regulation. Within all eukaryotic cells, mitochondria are responsible for synthesis of ATP among other metabolite needed for cell survival. VDAC1 therefore allows for communication between the mitochondrion and the cell mediating the balance between cell metabolism and cell death. Besides metabolic permeation, VDAC1 also acts as a scaffold for proteins such as hexokinase that can in turn regulate metabolism.
Omptins are a family of bacterial proteases. They are aspartate proteases, which cleave peptides with the use of a water molecule. Found in the outer membrane of gram-negative enterobacteria such as Shigella flexneri, Yersinia pestis, Escherichia coli, and Salmonella enterica. Omptins consist of a widely conserved beta barrel spanning the membrane with 5 extracellular loops. These loops are responsible for the various substrate specificities. These proteases rely upon binding of lipopolysaccharide for activity.
In molecular biology, the OmpA domain is a conserved protein domain with a beta/alpha/beta/alpha-beta(2) structure found in the C-terminal region of many Gram-negative bacterial outer membrane proteins, such as porin-like integral membrane proteins, small lipid-anchored proteins, and MotB proton channels. The N-terminal half of these proteins is variable although some of the proteins in this group have the OmpA-like transmembrane domain at the N terminus. OmpA from Escherichia coli is required for pathogenesis, and can interact with host receptor molecules. MotB serve two functions in E. coli, the MotA(4)-MotB(2) complex attaches to the cell wall via MotB to form the stator of the flagellar motor, and the MotA-MotB complex couples the flow of ions across the cell membrane to movement of the rotor.
In molecular biology, trimeric autotransporter adhesins (TAAs), are proteins found on the outer membrane of Gram-negative bacteria. Bacteria use TAAs in order to infect their host cells via a process called cell adhesion. TAAs also go by another name, oligomeric coiled-coil adhesins, which is shortened to OCAs. In essence, they are virulence factors, factors that make the bacteria harmful and infective to the host organism.
OmpT is an aspartyl protease found on the outer membrane of Escherichia coli. OmpT is a subtype of the family of omptin proteases, which are found on some gram-negative species of bacteria.
BamA is a β-barrel, outer membrane protein found in Gram-negative bacteria and it is the main and vital component of the β-barrel assembly machinery (BAM) complex in those bacteria. BAM Complex consists of five components; BamB, BamC, BamD, BamE and BamA. This complex is responsible in catalyzing folding and insertion of β-barrel proteins into the outer membrane of Gram-negative bacteria.
