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 carbox y-terminal end converts prohaemolysin into mature haemolysin. As the role o f the peptide removed from the mature haemolysin has not been studied, we m utated 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 signi ficantly reduced the efficiency of secretion of haemolysin into the culture supernatant. Mutant haemolysins with deletion of 10 amino acids were easil y degraded in cells. Furthermore, cross-linking experiments indicated that the haemolysins dimerize in cells, and thus dimerized haemolysins are trans located across the outer membrane and appear in the culture supernatant. Th ese results indicated that the carboxy-terminal end of prohaemolysin trigge rs dimerization of haemolysin in cells, resulting in the efficient secretio n of haemolysin into the culture supernatant. (C) 2000 Academic Press.