Analysis of differences in the functional properties of the substrate binding proteins of the Borrelia burgdorferi oligopeptide permease (Opp) operon.
The Borrelia burgdorferi genome encodes five orthologues of the substrate binding protein oligopeptide permease A (OppA). It was previously shown that these genes are under the control of separate promoters and are differentially expressed under various environmental conditions. We were interested in determining whether there are also differences in substrate specificities among the proteins. The substrate specificities of recombinant proteins were determined by screening for high-affinity peptides by use of a combinatorial phage display heptapeptide library. Different heptapeptides with high affinities for OppA-1, OppA-2, and OppA-3 were identified. No heptapeptide binding OppA-4 or OppA-5 could be identified. Competitive binding assays were performed under various conditions to determine the substrate preferences of the OppA proteins. OppA-1 retained maximal activity over a broad range of pHs (5.5 to 7.5), whereas OppA-2 and OppA-3 showed peak activities at pHs below 5.5. OppA-1 and OppA-2 showed preferences for tripeptides over dipeptides and longer-chain peptides. Although a wide variety of amino acyl side chains were tolerated by all three OppA proteins, OppA-1 showed the broadest substrate specificity and was able to accommodate peptides composed of bulky hydrophobic residues; OppA-2 and OppA-3 showed preferences for peptides composed of small nonpolar amino acids. All three OppA proteins showed preferences for peptides composed of L- rather than D-amino acids. OppA-3 showed the greatest tolerance for changes in stereochemistry. Substantial differences in the substrate specificities of the OppA proteins of B. burgdorferi suggest that they may have distinct functions in the organism.
Wang
Xing-Guo
XG
Tupper Research Institute, Division of Geographic Medicine and Infectious Diseases, New England Medical Center, Boston, Massachusetts 02111, USA.
Kidder
J Michael
JM
Scagliotti
Joanna P
JP
Klempner
Mark S
MS
Noring
Richard
R
Hu
Linden T
LT
D001426:Bacterial Proteins; D001667:Binding, Competitive; D025065:Borrelia burgdorferi / Q000235:genetics / Q000378:metabolism*; D002352:Carrier Proteins / Q000737:chemistry* / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D020650:Combinatorial Chemistry Techniques; D015964:Gene Expression Regulation, Bacterial; D006863:Hydrogen-Ion Concentration; D008074:Lipoproteins / Q000737:chemistry* / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D009842:Oligopeptides / Q000378:metabolism*; D009876:Operon; D019151:Peptide Library; D013237:Stereoisomerism; D013379:Substrate Specificity
D001426:Bacterial Proteins; D002352:Carrier Proteins; D008074:Lipoproteins; D009842:Oligopeptides; D019151:Peptide Library; C046506:oligopeptide-binding protein, bacteria