Glycosylase enzymes are a family of enzymes involved in the repair of DNA.
The primary mechanism by which they work is base excision repair. Base excision repair is a DNA repair process which removes the old, damaged DNA and replaces it with new, fresh DNA without errors.
Glyocylases are involved in catalyzing the first step of this process, allowing for the removal of the section of DNA requiring repair. DNA glycosylases interact with the damaged nitrogenous section of the DNA while leaving the backbone structure intact. This action then allows the remainder of the repair process to get underway, permitting the creation and insertion of new DNA at the site. Researchers usually call the area free from nitrogenous DNA the AP Site. DNA glycosylases excise uracil residuals from DNA. They do this by cutting the N-glycosidic bond, which begins the DNA excision repair process. Some uracil residues can damage the DNA - they are genotoxic.
Monofunctional glycosylases have a single purpose: to cut out the damaged section of DNA. They must work in synchrony with other enzymes to ensure that the process works properly.
Bifunctional glycosylases. Bifunctional glycosylases, as the name implies, have two functions. These glycosylases can cut the phosphodiester bond of DNA and create a single-strand break without the assistance of AP endonuclease. This is because the enzyme has AP lyase activity.
Glycosylase enzymes have a 3-layer alpha-beta-alpha structure - similar to a classic alpha/beta protein. The structure consists of four-stranded, all-parallel beta-sheets surrounded by eight alpha-helices. The technical term for this structure is a “parallel doubly wound beta-sheet.”
It is suggested that cancer initiatives and proliferates because it can alter the epigenome Researchers are asking whether DNA glycosylase genes may have a role to play. The better the performance of these genes, the more DNA repair. Researchers believe that there may be mutations of the epigenome, which may cause glycosylase to work less efficiently.
Cells need a glycosylase called MBD4, for instance, to perform base excision repair of the genome. In some cancers, however, MBD4 expression is reduced - colorectal cancer being an example. Without the expression of this enzyme and the gene which codes for it, the enzyme cannot make the correct incision in the genome at the correct site, and this may be a driving factor behind genotoxicity.