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To understand the mechanisms of tryptophan synthase, the structure of the enzyme must first be studied. The general form of the enzyme is an α2β2 complex in which the α subunit forms a TIM barrel and the β subunit has a type II fold conformation.^[1] Additionally, the enzyme has two binding sites: an indole 3-glycerol binding site and an indole and serine binding site. Another important feature that allows for the tryptophan synthase to perform its function is its hydrophobic channel which makes it possible for indoles to diffuse to the appropriate site instead of diffusing out to cell’s cytosol.^[2]

Function

The mechanism of tryptophan synthase can be described in two steps. These steps are the last two in the synthesis of tryptophan. They include the loss of glyceraldehyde 3-phosphate from indole 3-glyserinphosphate forming indole and then the change from indole into tryptophan via the binding of serine and loss of water.

Relevance

The production of tryptophan takes place not in animals but in all other kingdoms such as plants, fungi, and bacteria because the enzyme is only present in these organisms. If humans could somehow inhibit this enzyme in those organisms, it would be an effective way to treat certain diseases without having harmful effects on humans. Such diseases as tuberculosis, ocular and genital infections, and cryptosporidiosis could be potential targets and, herbicides could be made using chemicals which inhibit this enzyme in plants as well.

Structural highlights

The structure of Tryptophan Synthase is in an alpha-beta-beta-alpha complex with two binding sites: an indole 3-glycerol binding site and an indole and serine binding site.In Salmonella typhimurium, studies have shown the relevance of its monovalent cation site (MVC), which is necessary for catalysis and regulation of substrate channeling ^[3]. This site is also directly related to the reaction between the α2β2 complex of tryptophan synthase and the L-serine by regulating the distribution of intermediates within this reaction.It activates Tryptophan synthase by binding to its allosteric site which is positioned near the PLP cofactor of the enzyme ^[4]. Examples of these cations bounded by the enzyme in vitro include Sodium, Potassium, Cesium, Lithium, Rubidium, Ammonium, and Guanidinium ions.