The thioredoxin fold is a

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 ...

fold common to

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 that catalyze

disulfide bond In biochemistry, a disulfide (or disulphide in British English) refers to a functional group with the structure . The linkage is also called an SS-bond or sometimes a disulfide bridge and is usually derived by the coupling of two thiol groups. In ...

formation and

isomer In chemistry, isomers are molecules or polyatomic ions with identical molecular formulae – that is, same number of atoms of each element – but distinct arrangements of atoms in space. Isomerism is existence or possibility of isomers. Iso ...

ization. The fold is named for the canonical example

thioredoxin Thioredoxin is a class of small redox proteins known to be present in all organisms. It plays a role in many important biological processes, including redox signaling. In humans, thioredoxins are encoded by ''TXN'' and '' TXN2'' genes. Loss-of-fu ...

and is found in both

prokaryotic A prokaryote () is a Unicellular organism, single-celled organism that lacks a cell nucleus, nucleus and other membrane-bound organelles. The word ''prokaryote'' comes from the Greek language, Greek wikt:πρό#Ancient Greek, πρό (, 'before') a ...

and

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 ...

proteins. It is an example of an alpha/beta protein fold that has

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 ...

activity. The fold's spatial topology consists of a four-stranded antiparallel

beta sheet The beta sheet, (β-sheet) (also β-pleated sheet) is a common motif of the regular protein secondary structure. Beta sheets consist of beta strands (β-strands) connected laterally by at least two or three backbone hydrogen bonds, forming a g ...

sandwiched between three

alpha helices The alpha helix (α-helix) is a common motif in the secondary structure of proteins and is a right hand-helix conformation in which every backbone N−H group hydrogen bonds to the backbone C=O group of the amino acid located four residues ear ...

. The strand topology is 2134 with 3 antiparallel to the rest.

Sequence conservation

Despite sequence variability in many regions of the fold, thioredoxin proteins share a common

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 ...

sequence with two reactive

cysteine Cysteine (symbol Cys or C; ) is a semiessential proteinogenic amino acid with the formula . The thiol side chain in cysteine often participates in enzymatic reactions as a nucleophile. When present as a deprotonated catalytic residue, sometime ...

residues: Cys-X-Y-Cys, where X and Y are often but not necessarily

hydrophobic In chemistry, hydrophobicity is the physical property of a molecule that is seemingly repelled from a mass of water (known as a hydrophobe). In contrast, hydrophiles are attracted to water. Hydrophobic molecules tend to be nonpolar and, th ...

amino acid Amino acids are organic compounds that contain both amino and carboxylic acid functional groups. Although hundreds of amino acids exist in nature, by far the most important are the alpha-amino acids, which comprise proteins. Only 22 alpha am ...

s. The reduced form of the protein contains two free

thiol In organic chemistry, a thiol (; ), or thiol derivative, is any organosulfur compound of the form , where R represents an alkyl or other organic substituent. The functional group itself is referred to as either a thiol group or a sulfhydryl gro ...

groups at the cysteine residues, whereas the oxidized form contains a disulfide bond between them.

Disulfide bond formation

Different thioredoxin fold-containing proteins vary greatly in their reactivity and in the pKa of their free thiols, which derives from the ability of the overall protein structure to stabilize the activated

thiolate In organic chemistry, a thiol (; ), or thiol derivative, is any organosulfur compound of the form , where R represents an alkyl or other organic substituent. The functional group itself is referred to as either a thiol group or a sulfhydryl grou ...

. Although the structure is fairly consistent among proteins containing the thioredoxin fold, the pKa is extremely sensitive to small variations in structure, especially in the placement of protein backbone atoms near the first cysteine.

Examples

Human proteins containing this domain include: * DNAJC10 * ERP70 *

GLRX3 Glutaredoxin-3 is a protein that in humans is encoded by the ''GLRX3'' gene. Interactions GLRX3 has been shown to interact with PRKCQ Protein kinase C theta (PKC-θ) is an enzyme that in humans is encoded by the ''PRKCQ'' gene. PKC-θ, a member ...

P4HB Protein disulfide-isomerase, also known as the beta- subunit of prolyl 4-hydroxylase (P4HB), is an enzyme that in humans encoded by the ''P4HB'' gene. The human ''P4HB'' gene is localized in chromosome 17q25. Unlike other prolyl 4-hydroxylase fami ...

;

PDIA2 Protein disulfide isomerase family A member 2 is a protein that in humans is encoded by the PDIA2 gene. Function This gene encodes a member of the disulfide isomerase (PDI) family of endoplasmic reticulum (ER) proteins that catalyze protein ...

;

PDIA3 Protein disulfide-isomerase A3 (PDIA3), also known as glucose-regulated protein, 58-kD (GRP58), is an isomerase enzyme. This protein localizes to the endoplasmic reticulum (ER) and interacts with lectin chaperones calreticulin and calnexin (CNX) ...

; PDIA4; PDIA5; PDIA6 (P5); PDILT * QSOX1; QSOX2 * STRF8 * TXN;

TXN2 Thioredoxin, mitochondrial also known as thioredoxin-2 is a protein that in humans is encoded by the ''TXN2'' gene on chromosome 22. This nuclear gene encodes a mitochondrial member of the thioredoxin family, a group of small multifunctional redox ...

; TXNDC1; TXNDC10; TXNDC11; TXNDC13; TXNDC14; TXNDC15; TXNDC16; TXNDC2; TXNDC3;

TXNDC4 Endoplasmic reticulum resident protein 44 (ERp44) also known as thioredoxin domain-containing protein 4 (TXNDC4) is a protein that in humans is encoded by the ''ERP44'' gene. Interactions TXNDC4 has been shown to interact with ERO1L ERO1-lik ...

; TXNDC5; TXNDC6; TXNDC8; TXNL1; TXNL3

References

External links

SCOP thioredoxin superfamily

CATH glutaredoxin topology
{{DEFAULTSORT:Thioredoxin Fold Protein domains Protein folds