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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.
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 ...
Most of them are water-soluble outer membrane 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. [1]
There are two basic types of transmembrane proteins: [4] alpha-helical and beta barrels. Alpha-helical proteins are present in the inner membranes of bacterial cells or the plasma membrane of eukaryotic cells, and sometimes in the bacterial outer membrane. [5] This is the major category of transmembrane proteins.
β-barrel membrane proteins can only be found in the outer membrane of Gram-negative bacteria and in organelles such as mitochondria and chloroplasts which were evolved from bacteria. [8] [9] In Gram-negative bacteria, outer membrane proteins are synthesized in the cytoplasm and then exported into the periplasm by Sec translocon machinery. [10 ...
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.
Instead, the extracellular forms of these Gram-negative bacteria maintain their structural integrity by relying on a layer of disulfide bond cross-linked cysteine-rich proteins, which is located between cytoplasmic membrane and outer membrane in a manner analogous to the peptidoglycan layer in other Gram-negative bacteria. [4]
The glycocalyx is located on the apical surface of vascular endothelial cells which line the lumen.When vessels are stained with cationic dyes such as Alcian blue stain, transmission electron microscopy shows a small, irregularly shaped layer extending approximately 50–100 nm into the lumen of a blood vessel.