Proline Cis−Trans Isomerization and Protein Folding

Abstract

Proline cis-trans isomerization plays a key role in the rate-determining steps of protein folding. The energetic origin of this isomerization process is summarized, and the folding and unfolding of disulfide-intact bovine pancreatic ribonuclease A is used as an example to illustrate the kinetics and structural features of conformational changes from the heterogeneous unfolded state (consisting of cis and trans isomers of X-Pro peptide groups) to the native structure in which only one set of proline isomers is present.

Role of Proline Residues in the Folding of Serine Hydroxymethyltransferase

“…Pro Residues and Folding-The role of Pro residues in protein folding has been widely discussed and studied (14,15). Pro residues often act to slow down the folding process creating intermediates on the folding pathway.…”

“…Of particular interest is the role of cis Pro residues that often cap ␣-helices or are involved in ␤ turns. The reversible cis-trans interconversion of X-Pro peptide bonds exhibits a large enthalpy of activation of approximately 20 kcal mol Ϫ1 (15). In the unfolded state the equilibrium favors the more stable trans form by a 3 or 4 to 1 ratio.…”

“…Most Pro residues in proteins are trans, but approximately 6% are cis (16). In small proteins and some larger ones Pro isomerization can be the rate determining step in folding and because Pro residues exist as a mixture of isomers in the unfolded state leads to multiple parallel pathways in folding (15,17). In trying to discern the role of Pro residues in the folding of larger multidomain proteins, it is helpful to have structural information about intermediates in which Pro residues play a role.…”

An Arabidopsis ATP-Dependent, DEAD-Box RNA Helicase Loses Activity upon IsoAsp Formation but Is Restored by PROTEIN ISOASPARTYL METHYLTRANSFERASE

“…PRH75 has been reported to physically interact with at least two peptidyl-prolyl cis-trans isomerases (GeneMANIA; Razick et al, 2008;WardeFarley et al, 2010) responsible for altering the relative orientation of Pro and its N-terminal neighbor in the protein backbone (Galat, 1993). Nonenzymatic Pro isomerization is known to occur slowly, overcoming a considerable energy barrier (Chen et al, 2012), although this process accelerates with increasing temperature (Kern et al, 1997), resulting in deleterious consequences for enzymatic activity, should it not be rectified (Cloos and Christgau, 2002;Wedemeyer et al, 2002). It is possible that peptidyl-prolyl cis-trans isomerase association with PRH75 underlies a propensity for the helicase to also undergo Pro isomerization and deactivation over time, a subtle protein alteration that PIMT would be incapable of reversing.…”

Solvent and conformation dependence of amide I vibrations in peptides and proteins containing proline

“…Proline is a unique amino acid because the side chain binds to its backbone nitrogen forming a tertiary amide unit, which results in a lower vibrational amide I frequency than the secondary amide I unit found in other amino acids. Proline is typically located in γ-and β-turns of proteins and plays an important role in determining folding rates of proteins [43,44]. Proline is an integral amino acid in proteins in connective tissue such as elastin and collagen.…”