enzymology An enzyme () is a protein that acts as a biological catalyst by accelerating chemical reactions. The molecules upon which enzymes may act are called substrate (chemistry), substrates, and the enzyme converts the substrates into different mol ...

, a 2,3-dihydro-2,3-dihydroxybenzoate dehydrogenase () is an

enzyme An enzyme () is a protein that acts as a biological catalyst by accelerating chemical reactions. The molecules upon which enzymes may act are called substrate (chemistry), substrates, and the enzyme converts the substrates into different mol ...

that

catalyzes Catalysis () is the increase in rate of a chemical reaction due to an added substance known as a catalyst (). Catalysts are not consumed by the reaction and remain unchanged after it. If the reaction is rapid and the catalyst recycles quick ...

the

chemical reaction A chemical reaction is a process that leads to the chemistry, chemical transformation of one set of chemical substances to another. When chemical reactions occur, the atoms are rearranged and the reaction is accompanied by an Gibbs free energy, ...

:2,3-dihydro-2,3-dihydroxybenzoate + NAD⁺

\rightleftharpoons

2,3-dihydroxybenzoate + NADH + H⁺ Thus, the two substrates of this enzyme are 2,3-dihydro-2,3-dihydroxybenzoate and NAD⁺, whereas its 3

products Product may refer to: Business * Product (business), an item that can be offered to a market to satisfy the desire or need of a customer. * Product (project management), a deliverable or set of deliverables that contribute to a business solution ...

are 2,3-dihydroxybenzoate,

NADH Nicotinamide adenine dinucleotide (NAD) is a coenzyme central to metabolism. Found in all living cells, NAD is called a dinucleotide because it consists of two nucleotides joined through their phosphate groups. One nucleotide contains an ade ...

, and H⁺. This enzyme belongs to the family of

oxidoreductase In biochemistry, an oxidoreductase is an enzyme that catalyzes the transfer of electrons from one molecule, the reductant, also called the electron donor, to another, the oxidant, also called the electron acceptor. This group of enzymes usually ut ...

s, specifically those acting on the CH-CH group of donor with NAD+ or NADP+ as acceptor. 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 semitrivi ...

of this enzyme class is 2,3-dihydro-2,3-dihydroxybenzoate:NAD+ oxidoreductase. This enzyme is also called 2,3-diDHB dehydrogenase. This enzyme participates in biosynthesis of siderophore group nonribosomal.

Structure

2,3-diDHB dehydrogenase is a tetramer protein with dimension 65x69x43 Å. It has a crystallographic 222 symmetry, which exhibited for other members of short-chain oxireductase (SCOR) family of enzymes. The length of each monomer is 248 residues and the weight of the protein is 24647 Da. Each monomer consists of 7 beta-pleated sheets and 6 alpha helices. Although the structure of the binding protein is not clearly defined, it was proposed that the binding pocket is made out of Leu83, Met85, Arg138, Gly140, Met141, Ser176, Met181, Gln182 and Leu185. It was also speculated that Arg138 is a likely subunit that interacts with the carboxyl group of 2,3-diDHB. Since there was a strong indication of oxidation at C3 position, Ser176 and Gln182 interact with the C2-hydroxyl group in order for the stereo-selective reaction to occur.

Reaction mechanism

In times of limited iron number in the environment, the EntA reaction is irreversible physiologically. The exact mechanism for the reaction is unknown; however, the proposed reaction scheme for the reaction is as following:

Rate of reaction

The rate of the conversion reaction is determined by several factors. The regiochemical position of the carboxyl group and the 3-hydroxyl group plays one role in the reaction, in which the rate of reaction of 1,3-''cis''-substituted substrate gives about 40-fold higher k_cat/K_m value than the 1,3-trans-substituted substrate.

Roles in bacteria

''
E. coli ''Escherichia coli'' ( )Wells, J. C. (2000) Longman Pronunciation Dictionary. Harlow ngland Pearson Education Ltd. is a gram-negative, facultative anaerobic, rod-shaped, coliform bacterium of the genus ''Escherichia'' that is commonly foun ...
''

2,3-diDHB dehydrogenase catalyzes the

NAD NAD or Nad may refer to: Geography * Nad, County Cork, a village in Ireland * North American Datum, a series of geographic coordinate systems * North Atlantic Drift, an Atlantic Ocean current * Hobli, a subdivision of a taluka in southern Ind ...

⁺-dependent oxidation of 2,3-dihydro-2,3-dihydroxybenzoate to produce an aromatic compound 2,3-dihydroxybenzoic acid (2,3-DHB or simply DHB). In times of iron deficiency, iron uptake is controlled by three genes: ''ent'', ''fep'', and ''fes'' for synthesis, export, and uptake of ferric

Enterobactin Enterobactin (also known as enterochelin) is a high affinity siderophore that acquires iron for microbial systems. It is primarily found in Gram-negative bacteria, such as ''Escherichia coli'' and ''Salmonella typhimurium''. Enterobactin is the s ...

and its hydrolytic cleavage to release Fe³⁺ into the cell. This production of this compound is controlled by eight genes: entA-entF, entH, and entS. In E. coli, all of these genes are controlled by the Fur repressor, such that the genes are turned on when the concentration of iron in the environment is low. From these six genes, EntA, EntB, and EntC are responsible for the synthesis of DHB from

chorismic acid Chorismic acid, more commonly known as its ion, 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, ind ...

and the gene EntA encodes the information of 2,3-diDHB dehydrogenase. Without , , and , the bacteria show almost an absolute requirement of DHB in order to survive.

'' A. tumefaciens''

Production of siderophores also exhibited in some plant-infecting bacteria, such as ''Agrobacterium tumefaciens''. The enzyme is controlled by gene cluster agb and the production of 2,3-diDHB dehydrogenase is controlled by the gene agbA. The enzyme AgbA is homologous to the EntA enzyme in ''E. coli'', the same enzyme that produces 2,3-diDHB dehydrogenase.

References

{{Portal bar, Biology, border=no EC 1.3.1 NADH-dependent enzymes Enzymes of known structure