Chaperone involved in the correct folding and assembly of outer membrane proteins. Recognizes specific patterns of aromatic residues and the orientation of their side chains, which are found more frequently in integral outer membrane proteins. May act in both early periplasmic and late outer membrane-associated steps of protein maturation. [protein]-peptidylproline (omega=180) = [protein]-peptidylproline (omega=0) Is capable of associating with the outer membrane. The PPIase activity resides only in the second parvulin domain. The N-terminal region and the C-terminal tail are necessary and sufficient for the chaperone activity of SurA. The PPIase activity is dispensable for SurA to function as a chaperone. The N-terminal region and the C-terminal tail are also required for porin recognition.