Parvulin

Parvulin, a 92-amino acid protein discovered in E. coli in 1994,Rahfeld JU, Schierhorn A, Mann KH. (1994). A novel peptidyl-prolyl cis/trans isomerase from Escherichia coli. "FEBS Lett" 343:65.] is the smallest known protein with prolyl isomerase activity, which catalyzes the "cis"-"trans" isomerization of proline peptide bonds. Although parvulin has no homology with larger prolyl isomerases such as cyclophilin and FKBP, it does share structural features with subdomains of other proteins involved in preparing secreted proteins for export from the cell. Balbach J, Schmid FX. (2000). Proline isomerizarion and its catalysis in protein folding. "In Mechanisms of Protein Folding" 2nd ed. Ed. RH Pain. "Frontiers in Molecular Biology" series. Oxford University Press: Oxford, UK.]

Although parvulin is as active as the larger prolyl isomerases against a short proline-containing test peptide, it has lower relative activity against biological substrates, possibly because the larger molecules have a higher ability to bind the substrate peptide.Scholz C, Rahfeld J, Fischer G, Schmid FX. (1997). Catalysis of protein folding by parvulin. "J Mol Biol" 273(3):752-62.] Parvulin itself contains proline residues and its folding can be accelerated by the presence of cyclophilin; parvulin folding can also be autocatalytic.

A eukaryotic homolog of parvulin known as Pin1 is required to execute the transition from G2 phase to M phase in the cell cycle.Gothel SF, Marahiel MA. (1999). Peptidyl-prolyl cis-trans isomerases, a superfamily of ubiquitous folding catalysts. "Cell Mol Life Sci" 55(3):423-36.] Absence of Pin1 activity in humans has also been implicated in the folding and processing of the amyloid precursor protein, whose degradation product is the cytotoxic peptide amyloid beta implicated in Alzheimer's disease.Pastorino L, Sun A, Lu PJ, Zhou XZ, Balastik M, Finn G, Wulf G, Lim J, Li SH, Li X, Xia W, Nicholson LK, Lu KP. (2006). The prolyl isomerase Pin1 regulates amyloid precursor protein processing and amyloid-beta production. "Nature" 440(7083):528-34. ]

References