The effect of proline cis‐trans isomerization on the folding of the C‐terminal SH2 domain from p85

SH2 domains are protein domains that modulate protein–protein interactions through a specific interaction with sequences containing phosphorylated tyrosines. In this work, we analyze the folding pathway of the C‐terminal SH2 domain of the p85 regulatory subunit of the protein PI3K, which presents a proline residue in a cis configuration in the loop between the βE and βF strands. By employing single and double jump folding and unfolding experiments, we demonstrate the presence of an on‐pathway intermediate that transiently accumulates during (un)folding. By comparing the kinetics of folding of the wild‐type protein to that of a site‐directed variant of C‐SH2 in which the proline was replaced with an alanine, we demonstrate that this intermediate is dictated by the peptidyl prolyl cis‐trans isomerization. The results are discussed in the light of previous work on the effect of peptidyl prolyl cis‐trans isomerization on folding events.