|
Outer Membrane Efflux Proteins
Proteins in the outer membrane efflux protein family form trimeric (three-piece) channels that allow export of a variety of substrates in gram-negative bacteria. Each member of this family is composed of two repeats. The trimeric channel is composed of a 12-stranded beta-barrel that spans the outer membrane, and a long all helical barrel that spans the periplasm. Examples include the ''Escherichia coli ''Escherichia coli'' (),Wells, J. C. (2000) Longman Pronunciation Dictionary. Harlow ngland Pearson Education Ltd. also known as ''E. coli'' (), is a Gram-negative, facultative anaerobic, rod-shaped, coliform bacterium of the genus ''Escher ...'' TolC outer membrane protein, which is required for proper expression of outer membrane protein genes; the Rhizobium nodulation protein; and the Pseudomonas FusA protein, which is involved in resistance to fusaric acid. References * Protein domains Protein families Outer membrane proteins {{membrane-protein-stub ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Protein Family
A protein family is a group of evolutionarily related proteins. In many cases, a protein family has a corresponding gene family, in which each gene encodes a corresponding protein with a 1:1 relationship. The term "protein family" should not be confused with Family (biology), family as it is used in taxonomy. Proteins in a family descend from a common ancestor and typically have similar protein structure, three-dimensional structures, functions, and significant Sequence homology, sequence similarity. The most important of these is sequence similarity (usually amino-acid sequence), since it is the strictest indicator of homology and therefore the clearest indicator of common ancestry. A fairly well developed framework exists for evaluating the significance of similarity between a group of sequences using sequence alignment methods. Proteins that do not share a common ancestor are very unlikely to show statistically significant sequence similarity, making sequence alignment a powerf ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Gram-negative Bacteria
Gram-negative bacteria are bacteria that do not retain the crystal violet stain used in the Gram staining method of bacterial differentiation. They are characterized by their cell envelopes, which are composed of a thin peptidoglycan cell wall sandwiched between an inner cytoplasmic cell membrane and a bacterial outer membrane. Gram-negative bacteria are found in virtually all environments on Earth that support life. The gram-negative bacteria include the model organism ''Escherichia coli'', as well as many pathogenic bacteria, such as ''Pseudomonas aeruginosa'', '' Chlamydia trachomatis'', and ''Yersinia pestis''. They are a significant medical challenge as their outer membrane protects them from many antibiotics (including penicillin), detergents that would normally damage the inner cell membrane, and lysozyme, an antimicrobial enzyme produced by animals that forms part of the innate immune system. Additionally, the outer leaflet of this membrane comprises a complex lipopol ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Beta-barrel
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 (hydrogen bond). 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 (e.g., oxidase, dismutase, amylase) contain the beta barrel structure. In many cases, the strands contain alternating polar and non-polar (hydrophilic and hydrophobic) amino acids, so that the hydrophobic residues are oriented into the interior of the barrel to form a hy ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Bacterial Outer Membrane
The bacterial outer membrane is found in gram-negative bacteria. Its composition is distinct from that of the inner cytoplasmic cell membrane - among other things, the outer leaflet of the outer membrane of many gram-negative bacteria includes a complex lipopolysaccharide whose lipid portion acts as an endotoxin - and in some bacteria such as ''E. coli'' it is linked to the cell's peptidoglycan by Braun's lipoprotein. Porins can be found in this layer. Clinical significance If lipid A, part of the lipopolysaccharide, enters the circulatory system it causes a toxic reaction by activating toll like receptor TLR 4. Lipid A is very pathogenic and not immunogenic. However, the polysaccharide component is very immunogenic, but not pathogenic, causing an aggressive response by the immune system. The sufferer will have a high temperature and respiration rate and a low blood pressure. This may lead to endotoxic shock, which may be fatal. The bacterial outer membrane is physiologicall ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Periplasm
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., Matias, V. R., and T. J. Beveridge. 2005. Cryo-electron microscopy reveals native polymeric cell wall structure in Bacillus subtilis 168 and the existence of a periplasmic space. Mol. Microbiol. 56:240-251. ., Zuber B, Haenni M, Ribeiro T, Minnig K, Lopes F, Moreillon P, Dubochet J. 2006. Granular layer in the periplasmic space of Gram-positive bacteria and fine structures of Enterococcus gallinarum and Streptococcus gordonii septa revealed by cryo-electron microscopy of vitreous sections. J Bacteriol. 188:6652-6660. 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 bacteri ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Escherichia Coli
''Escherichia coli'' (),Wells, J. C. (2000) Longman Pronunciation Dictionary. Harlow ngland Pearson Education Ltd. also known as ''E. coli'' (), is a Gram-negative, facultative anaerobic, rod-shaped, coliform bacterium of the genus ''Escherichia'' that is commonly found in the lower intestine of warm-blooded organisms. Most ''E. coli'' strains are harmless, but some serotypes ( EPEC, ETEC etc.) can cause serious food poisoning in their hosts, and are occasionally responsible for food contamination incidents that prompt product recalls. Most strains do not cause disease in humans and are part of the normal microbiota of the gut; such strains are harmless or even beneficial to humans (although these strains tend to be less studied than the pathogenic ones). For example, some strains of ''E. coli'' benefit their hosts by producing vitamin K2 or by preventing the colonization of the intestine by pathogenic bacteria. These mutually beneficial relationships between ''E. col ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Protein Domains
In molecular biology, a protein domain is a region of a protein's polypeptide chain that is self-stabilizing and that folds independently from the rest. Each domain forms a compact folded three-dimensional structure. Many proteins consist of several domains, and a domain may appear in a variety of different proteins. Molecular evolution uses domains as building blocks and these may be recombined in different arrangements to create proteins with different functions. In general, domains vary in length from between about 50 amino acids up to 250 amino acids in length. The shortest domains, such as zinc fingers, are stabilized by metal ions or disulfide bridges. Domains often form functional units, such as the calcium-binding EF hand domain of calmodulin. Because they are independently stable, domains can be "swapped" by genetic engineering between one protein and another to make chimeric proteins. Background The concept of the domain was first proposed in 1973 by Wetlaufer after ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Protein Families
A protein family is a group of evolutionarily related proteins. In many cases, a protein family has a corresponding gene family, in which each gene encodes a corresponding protein with a 1:1 relationship. The term "protein family" should not be confused with family as it is used in taxonomy. Proteins in a family descend from a common ancestor and typically have similar three-dimensional structures, functions, and significant sequence similarity. The most important of these is sequence similarity (usually amino-acid sequence), since it is the strictest indicator of homology and therefore the clearest indicator of common ancestry. A fairly well developed framework exists for evaluating the significance of similarity between a group of sequences using sequence alignment methods. Proteins that do not share a common ancestor are very unlikely to show statistically significant sequence similarity, making sequence alignment a powerful tool for identifying the members of protein familie ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
