Biophysical characterization of the TraY protein of Escherichia coli F factor.
The TraY protein is required for efficient bacterial conjugation by Escherichia coli F factor. TraY has two functional roles: participating in the "relaxosome," a protein-DNA complex that nicks one strand of the F factor plasmid, and up-regulating transcription from the traYI promoter. The traY gene was cloned, and the TraY protein was expressed, purified, and characterized. TraY has a mixed alpha-helix and beta-sheet secondary structure as judged by its circular dichroism spectrum, is monomeric, and undergoes reversible urea denaturation with delta Gu = 6 kcal/mol at 25 degrees C. The kinetics of protein unfolding and refolding, as measured by changes in fluorescence, are complex, suggesting the presence of intermediates or of heterogeneity in the folding reaction. TraY has been classified as a member of the ribbon-helix-helix family of transcription factors but is unusual in appearing to have tandem repeats of the beta alpha alpha motif in the same polypeptide chain. The data presented here show that folding and assembly of the functional (beta alpha alpha)2 unit occurs as an intramolecular reaction and not by cross-folding between different polypeptide chains.
Schildbach
J F
JF
Department of Biology, Massachusetts Institute of Technology, Cambridge 02139, USA. joel@jhu.edu
Robinson
C R
CR
Sauer
R T
RT
D000595:Amino Acid Sequence; D002942:Circular Dichroism; D004268:DNA-Binding Proteins / Q000737:chemistry* / Q000302:isolation & purification; D004926:Escherichia coli; D029968:Escherichia coli Proteins; D005144:F Factor / Q000737:chemistry*; D007700:Kinetics; D008969:Molecular Sequence Data; D011487:Protein Conformation; D011489:Protein Denaturation; D017510:Protein Folding; D016415:Sequence Alignment; D013050:Spectrometry, Fluorescence
D004268:DNA-Binding Proteins; D029968:Escherichia coli Proteins; C063238:traY protein, E coli