Word origin: L, comb. form of trāns (adv. and prep.) across, beyond, through + -membrane.
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7. Beta-barrel – A beta barrel is a large beta-sheet that twists and coils to form a closed structure in which the first strand is hydrogen bonded to the last. Beta-strands in beta-barrels are typically arranged in an antiparallel fashion, porin-like barrel structures are encoded by as many as 2–3% of the genes in Gram-negative bacteria. All beta-barrels can be classified in terms of two parameters, the number of strands in the beta-sheet, n, and the shear number, S. These two parameters are related to the angle of the beta strands relative to the axis of the barrel. Sixteen- or eighteen-stranded beta barrel structures are common in porins, which function as transporters for ions, such structures appear in the outer membranes of gram-negative bacteria, chloroplasts, and mitochondria. The central pore of the protein, sometimes known as the eyelet, is lined with charged residues arranged so that the positive and negative charges appear on opposite sides of the pore. A long loop between two beta sheets partially occludes the channel, the exact size and conformation of the loop helps in discriminating between molecules passing through the transporter. Beta barrels also function within endosymbiont derived organelles such as mitochondria, within the mitochondrion two complexes exist with beta barrels serving as the pore forming subunit, Tom40 of the Translocase of the outer membrane, and Sam50 of the Sorting and assembly machinery. The chloroplast also has functionally similar beta barrel containing complexes, the best characterised of which is Toc75 of the TOC complex, lipocalins are typically eight-stranded beta barrel proteins that are often secreted into the extracellular environment. Their most distinctive feature is their ability to bind and transport small molecules in a beta barrel calyx. Examples of the family include retinol binding proteins and major urinary proteins, RBP binds and transports retinol, while Mups bind a number of small, organic pheromones, including 2-sec-butyl-4, 5-dihydrothiazole, 6-hydroxy-6-methyl-3-heptanone and 2,3 dihydro-exo-brevicomin. A piece of paper can be formed into a cylinder by bringing opposite sides together, the two edges come together to form a line. Shear can be created by sliding the two edges parallel to that line, likewise, a beta barrel can be formed by bringing the edges of a beta sheet together to form a cylinder. If those edges are displaced, then shear will be created, a similar definition of shear is found in geology, where shear refers to a displacement within rock perpendicular to the surface of the rock. In physics, the amount of displacement is referred to as shear strain, shear number is a measure of shear strain in which the displacement is measured in units of amino acid residues. The determination of shear number requires the assumption that each amino acid in one strand of a sheet is adjacent to just one amino acid in the neighboring strand. To illustrate, S will be calculated for green fluorescent protein and this protein was chosen because the beta barrel contains both parallel and antiparallel strands. The particular example used, PDB, 1RRX, is one of the few structures of protein that is not obtained from a mutant protein
Membrane proteins come in numerous types with a few different suggested classifications. One of the most commonly used to date is the classification method ...
A vesicular transport protein is a transmembrane or membrane associated protein . It regulates or facilitates the movement by vesicles of the contents of the cell. 
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Please use our web server or we can process your coordinates through email ( [email protected] ). All information is kept confidential. Orientation of membrane protein cannot be predicted if all its membrane-anchoring elements are missing or disordered.