Analysis of the clumping-mediating domain(s) of sex pheromone plasmid pAD1-encoded aggregation substance

Aggregation substance, a cell surface adhesin encoded on sex-pheromone plasmids exclusively found in the opportunistic pathogen Enterococcus faecalis, displays a dual function in that it mediates (a) adhesion to host tissues and (b) aggregation of E. faecalis cells to result in efficient plasmid transfer. While there have been many investigations regarding the regulation of inducible plasmid transfer and involvement in pathogenicity, nearly nothing is known about the structural basis of clumping capacity intrinsic to aggregation substance. Here, data are presented regarding the respective domain(s) of Asa1 (the adhesin encoded on plasmid pAD1) by analyzing the effects of in-frame deletions on clumping and by measuring binding of E. faecalis cells to surface-bound subfragments of aggregation substance. These data indicate that the N-terminal part of the adhesin is responsible for clumping, with a region between amino acid 525 and amino acid 617 playing a dominant role. Furthermore, by raising antibodies against different fragments of Asa1, it is shown that aggregation substance contains cross-reacting epitopes in its C-terminal and N-terminal parts, which could not be derived from their primary sequences.