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The outer membranes of a bacterium can contain a huge number of proteins. In E. Coli for example there are around 500,000 in the membrane. [5] Bacterial outer membrane proteins typically have a unique beta barrel structure that spans the membrane. The beta barrels fold to expose a hydrophobic surface before their insertion into the outer membrane.
Sixteen- or eighteen-stranded up-and-down beta barrel structures occur in porins, which function as transporters for ions and small molecules that cannot diffuse across a cellular membrane. Such structures appear in the outer membranes of gram-negative bacteria, chloroplasts, and mitochondria.
The chemical structure of the outer membrane's lipopolysaccharide is often unique to specific bacterial sub-species and is responsible for many of the antigenic properties of these strains. In addition to the peptidoglycan layer the Gram-negative cell wall also contains an additional outer membrane composed of phospholipids and ...
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. [1] BAM Complex consists of five components; BamB, BamC, BamD, BamE (all are lipoproteins ) and BamA (Outer membrane protein).
Efflux pumps generally consist of an outer membrane efflux protein, a middle periplasmic protein, an inner membrane protein, and a transmembrane duct. The transmembrane duct is located in the outer membrane of the cell. The duct is also bound to two other proteins: a periplasmic membrane protein and an integral membrane transporter.
The outer membrane complex is made up largely by the secretin GspD. [8] Secretins are β-barrels that are found in membrane where they form channels that allow substances to move in or out of cells. [9] In the type II secretion system GspD creates a pore in the outer membrane of the bacterial cell through which proteins can be secreted.
The trimeric channel is composed of a 12-stranded beta-barrel that spans the outer membrane, and a long tail helical barrel that spans the periplasm. Examples include the Escherichia coli TolC outer membrane protein, which is required for proper expression of outer membrane protein genes; the Rhizobium nodulation protein; and the Pseudomonas ...
All porins form homotrimers in the outer membrane, meaning that three identical porin subunits associate together to form a porin super-structure with three channels. [5] Hydrogen bonding and dipole-dipole interactions between each monomer in the homotrimer ensure that they do not dissociate, and remain together in the outer membrane.