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In epigenetics, proline isomerization is the effect that cis-trans isomerization of the amino acid proline has on the regulation of gene expression.Similar to aspartic acid, the amino acid proline has the rare property of being able to occupy both cis and trans isomers of its prolyl peptide bonds with ease.
From a kinetic standpoint, cis–trans proline isomerization is a very slow process that can impede the progress of protein folding by trapping one or more proline residues crucial for folding in the non-native isomer, especially when the native protein requires the cis isomer.
Proline is unique among the natural amino acids in having a relatively small difference in free energy between the cis configuration of its peptide bond and the more common trans form. The activation energy required to catalyse the isomerisation between cis and trans is relatively high: ~20kcal/mol (cf. ~0kcal/mol for
Peptidylprolyl isomerase A (PPIA), also known as cyclophilin A (CypA) or rotamase A is an enzyme that in humans is encoded by the PPIA gene on chromosome 7. [4] [5] [6] As a member of the peptidyl-prolyl cis-trans isomerase (PPIase) family, this protein catalyzes the cis-trans isomerization of proline imidic peptide bonds, which allows it to regulate many biological processes, including ...
Isomerization involves transforming a molecule so that it adopts a different structural conformation; proline isomerization plays an integral role in the modification of histone tails. [36] Fpr4 is the prolyl isomerase enzyme (PPIase) which converts the amino acid proline (P) on histones between the cis and trans conformations.
PPIases catalyze the cis-trans isomerization of proline imidic peptide bonds in oligopeptides and accelerate the folding of proteins. [6] Generally, PPIases are found in all eubacteria and eukaryotes, as well as in a few archaebacteria, and thus are highly conserved.
The isomerization energy, for example, for converting from a stable cis isomer to the less stable trans isomer is greater than for the reverse reaction, explaining why in the absence of isomerases or an outside energy source such as ultraviolet radiation a given cis isomer tends to be present in greater amounts than the trans isomer.
Peptidylprolyl isomerase D (cyclophilin D), also known as PPID, is an enzyme which in humans is encoded by the PPID gene on chromosome 4. As a member of the peptidyl-prolyl cis-trans isomerase (PPIase) family, this protein catalyzes the cis-trans isomerization of proline imidic peptide bonds, which allows it to facilitate folding or repair of proteins. [5]