Modification of autolysis by synthetic peptides derived from the presumptive binding domain of Staphylococcus aureus autolysin

The autolytic cell wall hydrolase of Staphylococcus aureus, Atl, contains t hree highly cationic repeats in the central region of the amino acid sequen ce, and the repeats are presumed to have the role of binding the enzyme to some components on the cell surface, To explain the possible function of th e repeats, me synthesized a number of 10- to 30-mer oligopeptides based on the Atl amino acid sequence (Thr432-Lys610) containing repeat I, and examin ed their effects on the autolysis of S, aureus cells. When the peptides wer e added to a cell suspension of S, aureus under low ionic strength conditio ns, five peptides, A10, A11, A14, A16 and B9, showed immediate increases in optical density (OD) of the cell suspension accompanied by decreases in vi able cell counts, After the immediate increases, the ODs for A10 and A14 ch anged little in the first 2 hr. In contrast, the ODs for A11 and A16 decrea sed rapidly When peptide A10 was added to suspensions of heat-killed whole cells, crude cell walls and a crude peptidoglycan preparation, their ODs we re increased approximately 2-fold, In contrast, the OD was not increased wh en the peptide was added to a suspension of pure peptidoglycan from which a nionic polymers had been removed. Light microscopic and transmission electr on microscopic study showed that A10 and A14 inhibited autolysis and that A 11 and A16 induced autolysis earlier than the control, These results sugges t strongly that the peptides adsorb to and precipitate on the anionic cell surface polymers such as teichoic acid and lipoteichoic acid via ionic inte raction, The effects of peptides on the autolysis mag be the results of the modification of S, aureus autolysin activities. These peptides, especially the 10-mer peptide B9 (PGTKLYTVPW) that represents the C-terminal half of A10 and N-terminal half of A11, may be important segments for Atl to bind t o the cell surface.