Targeting of muralytic enzymes to the cell division site of Gram-positive bacteria: repeat domains direct autolysin to the equatorial surface ring of Staphylococcus aureus

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Abstract
Staphylococcus aureus secretes autolysin (Atl) to complete cell division by hydrolyzing its thick cell wall layer at a designated site, known as the equatorial surface ring. Secreted pro‐Atl (1256 amino acids) is cleaved at residues 198 and 775 to generate a pro‐peptide, amidase and glucosaminidase, respectively. Here we examined the mechanism that directs amidase and glucosaminidase to the cell division site on the staphylococcal surface. Targeting of pro‐Atl to the cell surface occurred prior to its proteolytic processing. Three repeat domains (R1, R2 and R3) located at the center of pro‐Atl are necessary and sufficient for the targeting of reporter proteins to the equatorial surface ring. Pro‐Atl cleavage at residue 775 separates the polypeptide such that R1 and R2 are linked to the C‐terminus of amidase, whereas R3 is located at the N‐terminus of glucosaminidase. Thus, it appears that the repeat domains direct pro‐Atl, amidase and glucosaminidase to a specific receptor at the equatorial surface ring of staphylococci, thereby allowing localized peptidoglycan hydrolysis and separation of the dividing cells.