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Juers , Brian W. Matthews , Reuben E. Protein Science , 21 12 , Wheatley , John C. Kappelhoff , Jennifer N. Hahn , Megan L. Dugdale , Mark J. Dutkoski , Stephanie D. Tamman , Marie E. Fraser , Reuben E. Archives of Biochemistry and Biophysics , , FEBS Journal , 10 , They discovered that bacterial cells use it to sense when lactose is plentiful, providing the signal to turn the lac repressor on and off.
When lactose is plentiful, beta-galactosidase produces allolactose. This binds to the lac repressor and causes it to fall off the DNA, allowing production of enzymes and transporters for lactose utilization. Beta-galactosidase also breaks any extra allolactose into glucose and galactose, so nothing is wasted.
Beta-galactosidase is also an essential tool in the study of genetics, building on two discoveries about the enzyme. First, the enzyme is very specific for the galactose portion of lactose, but the glucose portion can be replaced with many alternative structures. In particular, scientists discovered that a dye could be used that turns blue when it is cleaved from the galactose portion. Biotech scientists use these dyes and truncated beta-galactosidase to report what is happening inside engineered bacteria.
A plasmid is constructed with a gene for the complementing peptide, and it is transfected into bacteria that have the truncated, inactive enzyme. Then, if the cell has taken up the plasmid, the peptide is made, beta-galactosidase is activated, and the cell turns blue when given the dye.
This plasmid is then modified to add a gene of interest in the middle of the peptide. If addition of the new gene fails, the plasmid will still turn the cell blue, but if the gene has been successfully added, it will destroy the complementing peptide and the cell will be colorless.
Beta-galactosidase has also been explored using cryo-electron microscopy. A cryo-EM map was built from over 90, images of the molecule frozen in ice, which was detailed enough to provide an atomic model. Image JSmol. Topics for Further Discussion The mechanism of the cleavage reaction has been studied with complexes of the enzyme with a variety of reaction intermediates.
The large beta-galactosidase enzyme may have evolved from smaller enzymes that perform similar reactions. References 5a1a: A. This enzyme is located in lysosomes, which are compartments within cells that break down and recycle different types of molecules. GM1 ganglioside is important for normal functioning of nerve cells in the brain, and keratan sulfate is particularly abundant in cartilage and the clear covering of the eye cornea.
Keratan sulfate belongs to a group of large sugar molecules called glycosaminoglycans GAGs or mucopolysaccharides. The GLB1 gene also provides instructions for making the elastin-binding protein.
On the cell surface, elastin-binding protein interacts with proteins called cathepsin A and neuraminidase 1 to form the elastin receptor complex. This receptor complex plays a role in the formation of elastic fibers, which are a component of the connective tissue that forms the body's supportive framework. As a result, these substances accumulate to toxic levels in many tissues and organs.
In the brain, progressive damage caused by the buildup of GM1 ganglioside leads to the destruction of nerve cells, which causes many of the signs and symptoms of GM1 gangliosidosis. Although the role elastin-binding protein plays in the development of GM1 gangliosidosis is unclear, the alteration of this protein may contribute to the weakened heart muscle cardiomyopathy found in some people with GM1 gangliosidosis.
Most of these mutations change single nucleotides in the gene. The degradation of GM1 ganglioside is not affected by these mutations.
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