From Proteopediaproteopedia link
Crystallographic Structure of SurA first peptidyl-prolyl isomerase domain complexed with peptide NFTLKFWDIFRK
[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 periplasmic molecular chaperone protein SurA facilitates correct folding and maturation of outer membrane proteins in Gram-negative bacteria. It preferentially binds peptides that have a high fraction of aromatic amino acids. Phage display selections, isothermal titration calorimetry and crystallographic structure determination have been used to elucidate the basis of the binding specificity. The peptide recognition is imparted by the first peptidyl-prolyl isomerase (PPIase) domain of SurA. Crystal structures of complexes between peptides of sequence WEYIPNV and NFTLKFWDIFRK with the first PPIase domain of the Escherichia coli SurA protein at 1.3 A resolution, and of a complex between the dodecapeptide and a SurA fragment lacking the second PPIase domain at 3.4 A resolution, have been solved. SurA binds as a monomer to the heptapeptide in an extended conformation. It binds as a dimer to the dodecapeptide in an alpha-helical conformation, predicated on a substantial structural rearrangement of the SurA protein. In both cases, side-chains of aromatic residues of the peptides contribute a large fraction of the binding interactions. SurA therefore asserts a recognition preference for aromatic amino acids in a variety of sequence configurations by adopting alternative tertiary and quaternary structures to bind peptides in different conformations.
The periplasmic bacterial molecular chaperone SurA adapts its structure to bind peptides in different conformations to assert a sequence preference for aromatic residues.,Xu X, Wang S, Hu YX, McKay DB J Mol Biol. 2007 Oct 19;373(2):367-81. Epub 2007 Aug 15. PMID:17825319
From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.