From Proteopediaproteopedia link
Crystallographic Structure of SurA, a Molecular Chaperone that Facilitates Outer Membrane Porin Folding
[SURA_ECOLI] Chaperone involved in the correct folding and assembly of outer membrane proteins, such as OmpA, OmpF and LamB. 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. Essential for the survival of E.coli in stationary phase. Required for pilus biogenesis.   
Publication Abstract from PubMed
The SurA protein facilitates correct folding of outer membrane proteins in gram-negative bacteria. The sequence of Escherichia coli SurA presents four segments, two of which are peptidyl-prolyl isomerases (PPIases); the crystal structure reveals an asymmetric dumbbell, in which the amino-terminal, carboxy-terminal, and first PPIase segments of the sequence form a core structural module, and the second PPIase segment is a satellite domain tethered approximately 30 A from this module. The core module, which is implicated in membrane protein folding, has a novel fold that includes an extended crevice. Crystal contacts show that peptides bind within the crevice, suggesting a model for chaperone activity whereby segments of polypeptide may be repetitively sequestered and released during the membrane protein-folding process.
Crystallographic structure of SurA, a molecular chaperone that facilitates folding of outer membrane porins.,Bitto E, McKay DB Structure. 2002 Nov;10(11):1489-98. PMID:12429090
From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.