Carboxy terminal region of haemolysin of Aeromonas sobria triggers dimerization

Haemolysin of Aeromonas sobria is released into the culture supernatant in the form of prohaemolysin. Removal of a 42 amino acid peptide at the carboxy-terminal end converts prohaemolysin into mature haemolysin. As the role of the peptide removed from the mature haemolysin has not been studied, we mutated the haemolysin genes to delete several amino acid residues from the carboxy terminus, expressed the mutant genes in A. sobria and analysed the haemolysins produced. Deletion of more than three amino acid residues significantly reduced the efficiency of secretion of haemolysin into the culture supernatant. Mutant haemolysins with deletion of 10 amino acids were easily degraded in cells. Furthermore, cross-linking experiments indicated that the haemolysins dimerize in cells, and thus dimerized haemolysins are translocated across the outer membrane and appear in the culture supernatant. These results indicated that the carboxy-terminal end of prohaemolysin triggers dimerization of haemolysin in cells, resulting in the efficient secretion of haemolysin into the culture supernatant.