Thiol:disulfide interchange protein DsbC
Escherichia coli (bacteria)
Proteins are linear polypeptides. The carboxylate group of one amino acid residue releases one oxygen and its carbon atom forms a bond with the amide nitrogen of the next residue, in the process generating one molecule of water for each such peptide bond formed. Sidechains may sometimes have sugars, phosphates or other chemical groups attached. No residue-residue bonds exist other than the peptide bond - with one exception. Cysteine residues contain a sulfur atom, attached to the peptide carbon through an intermediate carbon atom. If the sulfur atoms of two cysteine residues are sufficiently close, they may form a bond which is about 2.1 angstrom long, longer than normal bonds. This is called a disulfide bond. Disulfide bonds may exist between cysteines belonging to one chain (intramolecular bonds) or they may form between cysteines belonging to different chains (inter- molecular bonds). There are also so-called hydrogen bonds, where a proton is shared between two atoms, but they are too long to be considered bonds in the true chemical sense. Disulfide bonds provide additional stability to a folded polypeptide or they make sure that different subunits of a protein that should be close to each other stay close to each other. When a protein chain has been synthesized, it folds, possibly with help of so-called chaperonin proteins, into its 3-dimensional form. During this process it can happen that there will be disulfide bonds connecting the wrong cysteines.
The protein seen here helps correct such mistakes. Its is a dimer made from two subunits, both with a catalytic site to break and rearrange disulfide bonds. The protein is shaped like the letter V and the catalytic sites are located on the top of the two arms of the letter V. In addition the shape of the large cavity formed by the two subunits may act like a chaperonin, binding a wrong folded protein and helping it refold while fixing wrongly connected disulfide cysteines.
Protein Data Bank (PDB)
McCarthy, A.A. Haebel, P.W. Torronen, A. Rybin, V. Baker, E.N. Metcalf, P.; "Crystal structure of the protein disulfide bond isomerase, DsbC, from Escherichia coli."; Nature Struct. Biol.; (2000) 7:196-199 PubMed:10700276.
author: Arno Paehler