In molecular biology,

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 ...

s containing the cyclodeaminase domain function in channeling one-

carbon Carbon () is a chemical element with the symbol C and atomic number 6. It is nonmetallic and tetravalent In chemistry, the valence (US spelling) or valency (British spelling) of an element is the measure of its combining capacity with o ...

units to the folate pool. In most cases, this

domain Domain may refer to: Mathematics *Domain of a function, the set of input values for which the (total) function is defined **Domain of definition of a partial function **Natural domain of a partial function **Domain of holomorphy of a function * Do ...

acts as a

formimidoyltetrahydrofolate cyclodeaminase In enzymology, a formimidoyltetrahydrofolate cyclodeaminase () is an enzyme that catalyzes the chemical reaction :5-formimidoyltetrahydrofolate \rightleftharpoons 5,10-methenyltetrahydrofolate + NH3 Hence, this enzyme has one substrate, 5-formi ...

, which catalyses the cyclisation of formimidoyltetrahydrofolate to methenyltetrahydrofolate as shown in reaction (1). In the methylotrophic

bacterium 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 ...

Methylobacterium extorquens ''Methylorubrum extorquens'' is a Gram-negative bacterium. ''Methylorubrum'' species often appear pink, and are classified as pink-pigmented facultative methylotrophs, or Pink-Pigmented Facultative Methylotrophs, PPFMs. The wild type has been kn ...

'', however, it acts as a methenyltetrahydrofolate cyclohydrolase, which catalyses the interconversion of formyltetrahydrofolate and methylenetetrahydrofolate, as shown in reaction (2). (1) 5-formimidoyltetrahydrofolate = 5,10-methenyltetrahydrofolate + NH(3) (2) 10- formyltetrahydrofolate = 5,10-methenyltetrahydrofolate + H(2)O In

prokaryotes A prokaryote () is a single-celled organism that lacks a nucleus and other membrane-bound organelles. The word ''prokaryote'' comes from the Greek πρό (, 'before') and κάρυον (, 'nut' or 'kernel').Campbell, N. "Biology:Concepts & Connec ...

, this domain mostly occurs on its own, while in

eukaryotes Eukaryotes () are organisms whose cells have a nucleus. All animals, plants, fungi, and many unicellular organisms, are Eukaryotes. They belong to the group of organisms Eukaryota or Eukarya, which is one of the three domains of life. Bacte ...

it is fused to a

glutamate formiminotransferase Glutamate formimidoyltransferase is a methyltransferase enzyme which uses tetrahydrofolate as part of histidine catabolism. It catalyses two reactions: * 5-formimidoyltetrahydrofolate + L-glutamate tetrahydrofolate + N-formimidoyl-L-glutamate ...

domain (which catalyses the previous step in the pathway) to form the bifunctional enzyme

formiminotransferase cyclodeaminase Formimidoyltransferase cyclodeaminase or formiminotransferase cyclodeaminase (symbol FTCD in humans) is an enzyme that catalyzes the conversion of formiminoglutamate and tetrahydrofolate into formiminotetrahydrofolate and glutamate. Role in pa ...

. The

eukaryotic Eukaryotes () are organisms whose cells have a nucleus. All animals, plants, fungi, and many unicellular organisms, are Eukaryotes. They belong to the group of organisms Eukaryota or Eukarya, which is one of the three domains of life. Bacte ...

enzyme is a circular

tetramer A tetramer () (''tetra-'', "four" + '' -mer'', "parts") is an oligomer formed from four monomers or subunits. The associated property is called ''tetramery''. An example from inorganic chemistry is titanium methoxide with the empirical formula Ti ...

of homodimers, while the prokaryotic enzyme is a

dimer Dimer may refer to: * Dimer (chemistry), a chemical structure formed from two similar sub-units ** Protein dimer, a protein quaternary structure ** d-dimer * Dimer model, an item in statistical mechanics, based on ''domino tiling'' * Julius Dimer ( ...

. The

crystal structure In crystallography, crystal structure is a description of the ordered arrangement of atoms, ions or molecules in a crystal, crystalline material. Ordered structures occur from the intrinsic nature of the constituent particles to form symmetric pat ...

of the cyclodeaminase enzyme from ''Thermaotogoa maritima'' has been studied. It is a homodimer, where each

monomer In chemistry, a monomer ( ; ''mono-'', "one" + '' -mer'', "part") is a molecule that can react together with other monomer molecules to form a larger polymer chain or three-dimensional network in a process called polymerization. Classification Mo ...

is composed of six alpha helices arranged in an up and down helical bundle, forming a novel

fold Fold, folding or foldable may refer to: Arts, entertainment, and media * ''Fold'' (album), the debut release by Australian rock band Epicure *Fold (poker), in the game of poker, to discard one's hand and forfeit interest in the current pot *Above ...

. The location of the

active site In biology and biochemistry, the active site is the region of an enzyme where substrate molecules bind and undergo a chemical reaction. The active site consists of amino acid residues that form temporary bonds with the substrate (binding site) a ...

is not known, but

sequence alignment In bioinformatics, a sequence alignment is a way of arranging the sequences of DNA, RNA, or protein to identify regions of similarity that may be a consequence of functional, structural, or evolutionary relationships between the sequences. Alig ...

s revealed two clusters of conserved

residue Residue may refer to: Chemistry and biology * An amino acid, within a peptide chain * Crop residue, materials left after agricultural processes * Pesticide residue, refers to the pesticides that may remain on or in food after they are applie ...

s located in a deep pocket within the dimmer interface. This pocket was large enough to accommodate the reaction product and it was postulated that this is the active site.

References

{{InterPro content, IPR007044 Protein families