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= L-aspartate oxidase = From Wikipedia, the free encyclopedia Jump to navigation				Jump to search

Introduction
L-aspartate oxidase has an important anabolic role in prokaryotes by assisting in the production of nicotinamide adenine dinucleotide (NAD+) and reducing flavine adenine dinucleotide (FAD+). Leading researchers have used this knowledge in drug design to target pathogenic bacteria by inhibiting this mechanism. The mechanism of L-aspartate oxidase is also utilized in the tricarboxylic acid cycle, specifically in the succinate/fumarate redox reaction. This is catalyzed in the domains of the enzyme which is characterized by different alpha helices and beta sheets. In pharmaceutical research, organisms such as Sulfolobus tokodaii  which contain L-aspartate oxidase have been studied to create artificial sweeteners.

Structure and Function
L-aspartate oxidase, also known as LASPO, is the first catalyst involved in the bacterial de novo NAD+ biosynthesis pathway. It is an enzyme that has been discovered to convert L-aspartate to iminoaspartate and hydrogen peroxide. It does this conversion by using either molecular oxygen or fumarate that serve as the electron acceptors. Its catalytic cycle consists of a reductive and oxidative half-reaction by using both oxygen and fumarate as electron acceptors for flavine adenine dinucleotide (FAD) oxidation. In effect, this makes LASPO unusual compared to the other members of it’s class. In addition, LASPO can serve as an L-aspartate/fumarate oxidoreductase by creating imino-aspartate and succinate which allows LASPO to be physiologically functional in aerobic and anaerobic conditions.

In regards to its structure, it is very similar to the subunits found in succinate dehydrogenase (SDH) and fumarate reductase (FRD). The structural similarities found between LASPO, SDH, and FAD have led researchers to conclude that there are also many functional properties shared between them. For instance, they are all able to catalyze fumarate reduction. However, although SDH and FRD can oxidise succinate, LASPO is unable to do this.

Researchers have found that LASPO folds in three domains known as: the FAD-binding domain (represented by the color red in figure 1), the capping domain (represented by the color cyan in figure 1), and the helical domain (represented by the color green in figure 1). LASPO folds specifically on residues 2-241 and 353-410 in the FAD-binding domain which consists of a five-stranded parallel β sheet. Furthermore, LASPO folds specifically on residues 242-352 in the capping domain. Finally, LASPO folds specifically on residues 414-533 in the helical domain.

The C-terminal helical domain is found next to the FAD-binding domain. A polypeptide chain links the FAD-binding domain and C-terminal helical domain together whereas the FAD-binding domain is linked to the capping domain by a two stranded β sheet. The helical domain consists of three helices that wrap around each other known as: helixα1, helixα2, and helixα3. However, helixα3 is the only one that interacts with the FAD-binding domain. Moreover, the capping domain consists of three-stranded antiparallel β sheet that are flanked by four α helices.

Pharmaceutical use
L-aspartate oxidase (LAO) has a huge role in the biotechnology industry. The gene coding for LAO has been isolated in studies cultured from different species as they try to genetically increase its binding affinity and increase its speed. In the pharmaceuticals D-aspartate is useful “for parenteral nutrition, as food additive and in sweetener manufacturing”. As studies have shown with the use of genetically modified from thermophilic archaea Sulfolobus tokodaii LAO they have been able to convert racemic mixtures of D,L- aspartate. To make it more economical, scientist have been trying to make this enzyme more reusable so as to reduce the cost. In a study done by Armenia, Ilaria & Belzaretti (2017), the use of nanotechnology (NP) has made it much more easier to immobilize the enzyme. Hence they can use the LAO derived from Sulfolobus tokodaii to reduce the high cost per use associated with it.