Galactoside permease is a protein coded by the lacY gene of the lac operon, and is found bound to the membrane of a cell for the purpose of binding galactoside molecules that have been solubilized. The protein is part of a system whose main function is to catalyze the accumulation and transport of lactose and other beta-galactosides across the permeable barrier of a membrane. [1] [2]
Beta-galactoside permeases can describe any transport proteins that enable a cell to uptake, and thus accumulate, beta-galactosides. One known example of these transport proteins is the melibiose, or melB, carrier protein derived from the melB gene of E. coli. [3] This strain of beta-galactoside permease is known it transport melibiose and other galactosides across the cell membrane using hydrogen, sodium, or lithium ions in cotransport. [4]
Early studies by Hiroshi Nikaido in 1962 suggest a direct relationship between the amount of beta-galactoside permease activity in a cell and the turnover rate of phospholipids in E. coli. In his experiments with gram-positive and gram-negative bacterial cells under varying conditions, the level of P32 in phospholipids was found to be increased under conditions of maximal activity in beta-galactoside permease. Insofar, Nikaido concluded that this correlation suggested that phospholipids are involved in the process of transporting beta-galactosides through the cell membrane. [5] However, later research in 1965 by Alvin Tarlov and Eugene Kennedy using carbon tracers reveals increased levels of glycerol and serine, in addition to those of phosphorus, in the presence of increasing levels of beta-galactoside accumulation. The existence of these otherwise inert amino acids in relation to increasing levels of galactosides indicates a far less direct correlation between increasing levels of permease activity with increasing amounts of inorganic phosphate in the cell. [6]
β-Galactosidase, is a glycoside hydrolase enzyme that catalyzes hydrolysis of terminal non-reducing β-D-galactose residues in β-D-galactosides.
The lactose operon is an operon required for the transport and metabolism of lactose in E. coli and many other enteric bacteria. Although glucose is the preferred carbon source for most enteric bacteria, the lac operon allows for the effective digestion of lactose when glucose is not available through the activity of beta-galactosidase. Gene regulation of the lac operon was the first genetic regulatory mechanism to be understood clearly, so it has become a foremost example of prokaryotic gene regulation. It is often discussed in introductory molecular and cellular biology classes for this reason. This lactose metabolism system was used by François Jacob and Jacques Monod to determine how a biological cell knows which enzyme to synthesize. Their work on the lac operon won them the Nobel Prize in Physiology in 1965.
PEP group translocation, also known as the phosphotransferase system or PTS, is a distinct method used by bacteria for sugar uptake where the source of energy is from phosphoenolpyruvate (PEP). It is known to be a multicomponent system that always involves enzymes of the plasma membrane and those in the cytoplasm.
Isopropyl β-d-1-thiogalactopyranoside (IPTG) is a molecular biology reagent. This compound is a molecular mimic of allolactose, a lactose metabolite that triggers transcription of the lac operon, and it is therefore used to induce protein expression where the gene is under the control of the lac operator.
The permeases are membrane transport proteins, a class of multipass transmembrane proteins that allow the diffusion of a specific molecule in or out of the cell in the direction of a concentration gradient, a form of facilitated diffusion.
The bacterial outer membrane is found in gram-negative bacteria. Gram-negative bacteria form two lipid bilayers in their cell envelopes - an inner membrane (IM) that encapsulates the cytoplasm, and an outer membrane (OM) that encapsulates the periplasm.
Galactoside acetyltransferase is an enzyme that transfers an acetyl group from acetyl-CoA to β-galactosides, glucosides and lactosides. It is coded for by the lacA gene of the lac operon in E. coli.
The galactose permease or GalP found in Escherichia coli is an integral membrane protein involved in the transport of monosaccharides, primarily hexoses, for utilization by E. coli in glycolysis and other metabolic and catabolic pathways (3,4). It is a member of the Major Facilitator Super Family (MFS) and is homologue of the human GLUT1 transporter (4). Below you will find descriptions of the structure, specificity, effects on homeostasis, expression, and regulation of GalP along with examples of several of its homologues.
Phosphatidylethanolamine (PE) is a class of phospholipids found in biological membranes. They are synthesized by the addition of cytidine diphosphate-ethanolamine to diglycerides, releasing cytidine monophosphate. S-Adenosyl methionine can subsequently methylate the amine of phosphatidylethanolamines to yield phosphatidylcholines.
Outer membrane phospholipase A1 (OMPLA) is an acyl hydrolase with a broad substrate specificity (EC:3.1.1.32.) from the bacterial outer membrane. It has been proposed that Ser164 is the active site of the protein
Carbon catabolite repression, or simply catabolite repression, is an important part of global control system of various bacteria and other microorganisms. Catabolite repression allows microorganisms to adapt quickly to a preferred carbon and energy source first. This is usually achieved through inhibition of synthesis of enzymes involved in catabolism of carbon sources other than the preferred one. The catabolite repression was first shown to be initiated by glucose and therefore sometimes referred to as the glucose effect. However, the term "glucose effect" is actually a misnomer since other carbon sources are known to induce catabolite repression.
Lactose permease is a membrane protein which is a member of the major facilitator superfamily. Lactose permease can be classified as a symporter, which uses the proton gradient towards the cell to transport β-galactosides such as lactose in the same direction into the cell.
The Arc system is a two-component system found in some bacteria that regulates gene expression in faculatative anaerobes such as Escheria coli. Two-component system means that it has a sensor molecule and a response regulator. Arc is an abbreviation for Anoxic Redox Control system. Arc systems are instrumental in maintaining energy metabolism during transcription of bacteria. The ArcA response regulator looks at growth conditions and expresses genes to best suit the bacteria. The Arc B sensor kinase, which is a tripartite protein, is membrane bound and can autophosphorylate.
Diauxic growth, diauxie or diphasic growth is any cell growth characterized by cellular growth in two phases. Diauxic growth, meaning double growth, is caused by the presence of two sugars on a culture growth media, one of which is easier for the target bacterium to metabolize. The preferred sugar is consumed first, which leads to rapid growth, followed by a lag phase. During the lag phase the cellular machinery used to metabolize the second sugar is activated and subsequently the second sugar is metabolized.
Howard Ronald Kaback was an American biochemist, known for Kabackosomes, the cell-free membrane transport vesicles. He was the brother of Michael M. Kaback, pediatrician and human geneticist, who developed a screening program to detect and prevent Tay–Sachs disease, a rare and fatal genetic disorder most common in Ashkenazi Jews.
The potassium (K+) uptake permease (KUP) family (TC# 2.A.72) is a member of the APC superfamily of secondary carriers. Proteins of the KUP/HAK/KT family include the KUP (TrkD) protein of E. coli and homologues in both Gram-positive and Gram-negative bacteria. High affinity (20 μM) K+ uptake systems (Hak1, TC# 2.A.72.2.1) of the yeast Debaryomyces occidentalis as well as the fungus, Neurospora crassa, and several homologues in plants have been characterized. Arabidopsis thaliana and other plants possess multiple KUP family paralogues. While many plant proteins cluster tightly together, the Hak1 proteins from yeast as well as the two Gram-positive and Gram-negative bacterial proteins are distantly related on the phylogenetic tree for the KUP family. All currently classified members of the KUP family can be found in the Transporter Classification Database.
Resistance-nodulation-division (RND) family transporters are a category of bacterial efflux pumps, especially identified in Gram-negative bacteria and located in the cytoplasmic membrane, that actively transport substrates. The RND superfamily includes seven families: the heavy metal efflux (HME), the hydrophobe/amphiphile efflux-1, the nodulation factor exporter family (NFE), the SecDF protein-secretion accessory protein family, the hydrophobe/amphiphile efflux-2 family, the eukaryotic sterol homeostasis family, and the hydrophobe/amphiphile efflux-3 family. These RND systems are involved in maintaining homeostasis of the cell, removal of toxic compounds, and export of virulence determinants. They have a broad substrate spectrum and can lead to the diminished activity of unrelated drug classes if over-expressed. The first reports of drug resistant bacterial infections were reported in the 1940s after the first mass production of antibiotics. Most of the RND superfamily transport systems are made of large polypeptide chains. RND proteins exist primarily in gram-negative bacteria but can also be found in gram-positive bacteria, archaea, and eukaryotes.
The PTS Lactose-N,N’-Diacetylchitobiose (Lac) Family includes several sequenced lactose porters of Gram-positive bacteria, as well as the Escherichia coli and Borrelia burgdorferi N,N'-diacetylchitobiose (Chb) porters. It is part of the PTS-GFL superfamily. The former can transport aromatic β-glucosides and cellobiose, as well as Chb. However, only Chb induces expression of the chb operon.
Marcos Boris Rotman was a Chilean American immunologist–molecular biologist and professor emeritus of Medical Science at Alpert Medical School of Brown University. He is widely recognized for performing the first single molecule experiments in biology. He died in July 2021 at the age of 96.
Major facilitator superfamily domain containing 6 like (MFSD6L) is a protein encoded by the MFSD6L gene in humans. The MFSD6L protein is a transmembrane protein that is part of the major facilitator superfamily (MFS) that uses chemiosmotic gradients to facilitate the transport of small solutes across cell membranes.
{{cite book}}: |website= ignored (help)