User:Mckennamillar/Invertase (β-fructofuranosidase)

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Enzyme classification (EC) numbers are a way to organize all of the known enzymes in terms of how they function. In the instance of invertase, its EC number is 3.2.1.26. All enzymes with the first number being 3, are enzymes that are hydrolases. This indicates that this enzyme functions by breaking molecules apart with the addition of water. Having 3.2 as the first two numbers indicates that the hydrolase is acting on a sugar. The third number 1, further specifies that the enzyme hydrolases O- and S- glycosyl compounds. The final number specifies that the specific protein is invertase.

In a paper published in 2013, the author discusses how invertase works inside of baker's yeast (Saccharomyces). Invertase works to catalyze the cleavage of sucrose into its two monosaccharides, glucose and fructose.1 This specific invertase (β-fructofuranosidase) cleaves the molecule from its fructose end resulting in the two monosaccharides. It does this by adding a hydrogen ion to the glycosidic atom by an imidazolium cation. From there, an unstable intermediate carbonium ion will be left behind by the leaving of an alcohol group. Finally, the nucleophilic oxygen atom from alcohol or water will attack the C-2 cation which will leave behind a fructose molecule. The active-site carboxylate anion will take action to help keep the unequal balance of electrons stabilized throughout this process.2

As mentioned previously, invertase is commonly found in bakers' yeast. One of the main reasons that bakers use this yeast is to help bread rise, but another reason is to help influence the increase of sugar in bread. This function is able to happen due to the presence of invertase since glucose and fructose is sweeter than sucrose is.3 When looking at invertase across different species of yeasts, it has been known to be more active in some more than others. The yeast that invertase is more active in is the yeast bakers use due to its higher sweetness levels.4

Continuing to look at invertase through Saccharomyces, it can be seen that it has a unique structure; that structure being an octameric quaternary structure. Within the octameric quaternary structure, two dimerization types can be seen that in turn, form the octamer structure. Dimerization is an important aspect of protein folding due to it increasing the affinity of substrate binding. The crystal structure shows that the invertase is made up of eight subunits. The octamer shape is made up of two different types of dimers, a “‘closed’ arrangement” and an “‘open’ assembly” dimer. Each of these types has two subunits located opposite from each other in the structure. The “‘closed’ arrangement” dimers have fourteen out of the 32 hydrogen bonds made between the catalytic domain which creates a tighter pocket for the ligand; in turn, this makes it more stable. In contrast, the “‘open’ assembly” dimers only have a few hydrogen bonds in the catalytic domain, and the interactions that strengthen the pocket come from the salt bridges between Asp-45 and Lys-385. With the weaker interactions being in the “‘open’ assembly", it causes more instability that results in a lower denaturing temperature and lower durability at high-speed centrifugation. The way that the two dimers assemble, creates an antiparallel β sheet composed of β sandwiches made from two β sheets.5

While the focus has been on invertase in Saccharomyces, one of the known active sites is in the invertase in Bifidobacterium longum and is located within the β-propeller domain. The β-propeller domain is the inside the funnel created by five blades. Some amino acids to note are, Asp-54 and Glu-235, which are on the first strand of blades 1 and 4, along with Asn-53, Gln-70, Trp-78, Ser-114, Arg-180 and Asp-181 in the fructofuranoside ring.6