Comparative Biochemical Studies on F and EDP208 Conjugative Pili

Abstract

EDP208 pili are encoded by a derepressed derivative of a naturally occurring lac plasmid, Folac (incompatibility group FV), originally isolated from Salmonella typhi. EDP208 pili are serologically unrelated to F pili and do not promote infection by F-specific RNA bacteriophages. They confer sensitivity to the F-specific filamentous DNA phages. EDP208-containing cells are multi-piliated and contain approximately 20 pili/cell. These pili contain a single polypeptide subunit of 11,500 daltons. EPD208-specific RNA phages were readily isolated from local sewage. These phages were somewhat smaller in diameter than the F-specific RNA phages and absorbed relatively weakly to EDP208 pili. Comparing EDP208 pilin to F, both contain the equivalent of 2-3 hexose units/subunit and blocked N-termini. EDP208 pilin contains 1 covalently linked phosphate residue/subunit, whereas the F pilin subunit contains 2 such residues. Although notable differences were found in the case of 3 or 4 amino acids, the overall amino acid compositions of F and EDP208 were very similar. The tryptic peptide maps of the 2 proteins contained 7 peptides with similar mobilities, suggesting considerable homology in their amino acid sequences. Substantial similarities were also noted in the secondary structures of F and EDP208 pilin on the basis of circular dichroism studies. The .alpha.-helix content of both proteins was 65-70%. X-ray fiber diffraction studies have indicated that the arrangements of subunits in F and EDP208 pili are also similar. It was concluded that F and EDP208 pili are closely related structures.