title: Diverse sequences are functional at the C-terminus of the E. coli periplasmic chaperone SurA.
abstract: SurA is a major periplasmic molecular chaperone in Escherichia coli and has been shown to assist the biogenesis of several outer membrane proteins. The C-terminal fragment of SurA folds into a short β-strand, which forms a small three-stranded anti-parallel β-sheet module with the N-terminal β-hairpin. We found that the length of the C-terminal fragment, rather than its exact amino acid composition, had a big impact on SurA function. To investigate the determinant factor of the C-terminal sequence, we created a library of SurA constructs randomized in the last 10 residues. We screened the library and randomly analyzed 19 constructs that displayed SurA activity. The C-termini of these constructs shared little sequence similarity, except that β-strand-forming residues were preferentially enriched. Three SurA constructs were expressed and purified for structural characterization. Circular dichroism and fluorescence spectroscopy analyses revealed that their structures were similar to the structure of the wild-type SurA. Our results suggest that for scaffolding purpose proteins may tolerate various sequences provided certain general requirements such as hydrophobicity and secondary structure propensity are satisfied. Furthermore, the sequence tolerance of SurA at the C-terminus indicates that this area is not likely to be involved in substrate binding.
authors.affiliation: Department of Chemistry, University of Kentucky, 305 Chemistry-Physics Building, Lexington, KY 40506-0055, USA.
authors.forename: Qian
authors.initials: Q
authors.lastname: Chai
authors.forename: Brent
authors.initials: B
authors.lastname: Ferrell
authors.forename: Meng
authors.initials: M
authors.lastname: Zhong
authors.forename: Xinyi
authors.initials: X
authors.lastname: Zhang
authors.forename: Cui
authors.initials: C
authors.lastname: Ye
authors.forename: Yinan
authors.initials: Y
authors.lastname: Wei
mesh_terms: D000595:Amino Acid Sequence; D001483:Base Sequence; D002352:Carrier Proteins / Q000737:chemistry* / Q000235:genetics* / Q000378:metabolism*; D002942:Circular Dichroism; D004926:Escherichia coli / Q000235:genetics; D029968:Escherichia coli Proteins / Q000737:chemistry* / Q000235:genetics* / Q000378:metabolism*; D005816:Genetic Complementation Test; D008969:Molecular Sequence Data; D009154:Mutation; D019151:Peptide Library; D019696:Peptidylprolyl Isomerase / Q000737:chemistry* / Q000235:genetics* / Q000378:metabolism*; D017433:Protein Structure, Secondary; D013050:Spectrometry, Fluorescence
chemical_list: D002352:Carrier Proteins; D029968:Escherichia coli Proteins; D019151:Peptide Library; C490900:SurA protein, E coli; D019696:Peptidylprolyl Isomerase
keywords: mutation; periplasmic molecular chaperone; random sequence library; sequence diversity