The

enzyme Enzymes () are proteins that act as biological catalysts by accelerating chemical reactions. The molecules upon which enzymes may act are called substrates, and the enzyme converts the substrates into different molecules known as products. A ...

3-dehydroquinate dehydratase () catalyzes the

chemical reaction A chemical reaction is a process that leads to the IUPAC nomenclature for organic transformations, chemical transformation of one set of chemical substances to another. Classically, chemical reactions encompass changes that only involve the pos ...

:3-dehydroquinate

\rightleftharpoons

3-dehydroshikimate + H₂O This enzyme belongs to the family of

lyase In biochemistry, a lyase is an enzyme that catalyzes the breaking (an elimination reaction) of various chemical bonds by means other than hydrolysis (a substitution reaction) and oxidation, often forming a new double bond or a new ring structure. ...

s, specifically the hydro-lyases, which cleave carbon-oxygen bonds. This enzyme participates in

phenylalanine, tyrosine and tryptophan biosynthesis Amino acid synthesis is the set of biochemical processes (metabolic pathways) by which the amino acids are produced. The substrates for these processes are various compounds in the organism's diet or growth media. Not all organisms are able to sy ...

Discovery

The

shikimate pathway The shikimate pathway (shikimic acid pathway) is a seven-step metabolic pathway used by bacteria, archaea, fungi, algae, some protozoans, and plants for the biosynthesis of folates and aromatic amino acids (tryptophan, phenylalanine, and tyrosine) ...

was determined to be a major biosynthetic route for the production of aromatic amino acids through the research of Bernhard Davis and David Sprinson.

Role in the shikimate pathway

3-Dehydroquinate Dehydratase is an

that catalyzes the third step of the shikimate pathway. The shikimate pathway is a biosynthetic pathway that allows plants, fungi, and bacteria to produce

aromatic amino acids An aromatic amino acid is an amino acid that includes an aromatic ring. Among the 20 standard amino acids, the following are classically considered aromatic: phenylalanine, tryptophan and tyrosine. Although histidine contains an aromatic ring, ...

. Mammals do not have this pathway, meaning that they must obtain these

essential amino acids An essential amino acid, or indispensable amino acid, is an amino acid that cannot be synthesized from scratch by the organism fast enough to supply its demand, and must therefore come from the diet. Of the 21 amino acids common to all life form ...

through their diet. Aromatic Amino acids include

Phenylalanine Phenylalanine (symbol Phe or F) is an essential α-amino acid with the formula . It can be viewed as a benzyl group substituted for the methyl group of alanine, or a phenyl group in place of a terminal hydrogen of alanine. This essential amino a ...

Tyrosine -Tyrosine or tyrosine (symbol Tyr or Y) or 4-hydroxyphenylalanine is one of the 20 standard amino acids that are used by cells to synthesize proteins. It is a non-essential amino acid with a polar side group. The word "tyrosine" is from the Gr ...

, and

Tryptophan Tryptophan (symbol Trp or W) is an α-amino acid that is used in the biosynthesis of proteins. Tryptophan contains an α-amino group, an α- carboxylic acid group, and a side chain indole, making it a polar molecule with a non-polar aromatic ...

. This enzyme dehydrates 3-Dehydroquinate, converting it to 3-Dehydroshikimate, as indicated in the adjacent diagram. This is the third step in the Shikimate pathway. It belongs to the family of

s, specifically the hydro-lyases, which cleave carbon-oxygen bonds. The

systematic name A systematic name is a name given in a systematic way to one unique group, organism, object or chemical substance, out of a specific population or collection. Systematic names are usually part of a nomenclature. A semisystematic name or semitrivial ...

of this enzyme class is 3-dehydroquinate hydro-lyase (3-dehydroshikimate-forming). This enzyme is one of the few examples of

convergent evolution Convergent evolution is the independent evolution of similar features in species of different periods or epochs in time. Convergent evolution creates analogous structures that have similar form or function but were not present in the last com ...

. The two separate versions of this enzyme have different amino acid sequences. 3-Dehydroquinate dehydratase is also commonly referred to as Dehydroquinate dehydratase and DHQD. Other names include 3-dehydroquinate hydrolase, DHQase, 3-dehydroquinase, 5-dehydroquinase, dehydroquinase, 5-dehydroquinate dehydratase, 5-dehydroquinate hydro-lyase, and 3-dehydroquinate hydro-lyase. Pymol1DHQDika2011

Evolutionary origins

Purposes of the products

The aromatic amino acids produced by the shikimate acid pathway are used by higher plants as protein building blocks and as precursors for several secondary metabolites. Examples of such secondary metabolites are plant pigments and compounds to defend against herbivores, insects, and UV light. The specific aromatic secondary metabolites produced, as well as when and in what quantities they are produced in, varies across different types of plants. Mammals consume essential amino acids in their diets, converting them to precursors for important substances such as neurotransmitters.

Convergent evolution

As mentioned previously, two classes of 3-Dehydroquinate Dehydratase exist, known as types I and II. These two versions have different amino acid sequences and different

secondary structure Protein secondary structure is the three dimensional conformational isomerism, form of ''local segments'' of proteins. The two most common Protein structure#Secondary structure, secondary structural elements are alpha helix, alpha helices and beta ...

s. Type I is present in fungi, plants, and some bacteria, for the biosynthesis of

chorismate Chorismic acid, more commonly known as its anionic form chorismate, is an important biochemical intermediate in plants and microorganisms. It is a precursor for: * The aromatic amino acids phenylalanine, tryptophan, and tyrosine * Indole, indole d ...

. It catalyzes the cis-dehydration of 3-Dehydroquinate via a covalent imine intermediate. Type I is heat liable and has K_m values in the low micromolar range. Type II is present in the quinate pathway of fungi and the shikimate pathway of most bacteria. It catalyzes a trans-dehydration using an enolate intermediate. It is heat stable and has K_m values one or two orders of magnitude higher than the Type I K_m values. The best studied type I

is from ''

Escherichia coli ''Escherichia coli'' (),Wells, J. C. (2000) Longman Pronunciation Dictionary. Harlow ngland Pearson Education Ltd. also known as ''E. coli'' (), is a Gram-negative, facultative anaerobic, rod-shaped, coliform bacterium of the genus ''Escher ...

'' (gene aroD) and related

bacteria Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria were among ...

. It is a

homodimeric In biochemistry, a protein dimer is a macromolecular complex formed by two protein monomers, or single proteins, which are usually non-covalently bound. Many macromolecules, such as proteins or nucleic acids, form dimers. The word ''dimer'' has ...

protein Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, respo ...

. In

fungi A fungus ( : fungi or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and molds, as well as the more familiar mushrooms. These organisms are classified as a kingdom, separately from ...

, dehydroquinase forms the core of the pentafunctional AROM complex, which catalyses five consecutive steps in the

. A

histidine Histidine (symbol His or H) is an essential amino acid that is used in the biosynthesis of proteins. It contains an α-amino group (which is in the protonated –NH3+ form under biological conditions), a carboxylic acid group (which is in the de ...

is involved in the

catalytic mechanism Enzyme catalysis is the increase in the rate of a process by a biological molecule, an "enzyme". Most enzymes are proteins, and most such processes are chemical reactions. Within the enzyme, generally catalysis occurs at a localized site, calle ...

Other purposes

3-Dehydroquinate Dehydratase is also an enzyme present in the process of the degradation of quinate. Both 3-Dehydroquinate and 3-Dehydroshikimate are intermediates in the reaction mechanism. The following image shows this process in Quinate Degradation. QuinatedegredationCMDR

Structure

Applications

The Shikimate pathway has become a focus of research into the development of herbicides and antimicrobial agents because it is an essential pathway in many plants, bacteria, and parasites but does not exist in mammals. Inhibitors of the shikimate pathway in mycobacterium have the potential of treating tuberculosis. Most of the 3-dehydroquinate-dehydratase in bacteria and higher plants is type I DHQD.