Synthesis, conformational analysis, and biological evaluation of peptides from E. coli P pilus proteins

Sammanfattning: Many bacteria utilize hairlike protein appendages (pili) to attach themselves to mucosal cell surfaces in the host organism. The pilus is assembled from protein subunits synthesized inside the bacteria and transported to the outer cell wall for incorporation into the growing pilus. During the transport the pilus proteins are attached to a chaperone that protects them from aggregation and protelotyic degradation. In this thesis, the molecular details of the interactions between E. coli chaperone PapD and synthetic peptides have been investigated. Peptides derived from the uropathogenic E. coli P pilus subunit proteins were synthesized according to the Fmoc solid phase synthesis strategy using different techniques. The binding of the chaperone PapD to the pilus protein derived peptides was investigated in an inhibition ELISA. We concluded that peptides from the adhesin PapG are the most efficient inhibitors of PapD. The inhibitory powers of two series of peptides where the amino acids in octamer PapG peptides had been changed, one by one, to alanine or serine pin-pointed three residues as essential for recognintion and binding of PapG peptides to PapD. In addition, backbone-backbone hydrogen bonding was critical for binding. The conformational propensities of 19-mer carboxyl terminal peptides derived from the pilus proteins were studied in solution using NMR- and CD spectroscopy. We concluded that the peptides derived from the pilus adhesin seemed to have a higher preference for extended, b-strand conformations than the other peptides in the study. We propose that the high binding affinity of PapG derived peptides for PapD is the result of a combination of a higher preference for extended structures as well as favourable side chain interactions with PapD.