Role of staphylococcal wall teichoic acid in targeting the major autolysin Atl.

Staphylococcal cell separation depends largely on the bifunctional autolysin Atl that is processed to amidase-R(1,2) and R(3)-glucosaminidase. These murein hydrolases are targeted via repeat domains (R) to the septal region of the cell surface, thereby allowing localized peptidoglycan hydrolysis and separation of the dividing cells. Here we show that targeting of the amidase repeats is based on an exclusion strategy mediated by wall teichoic acid (WTA). In Staphylococcus aureus wild-type, externally applied repeats (R(1,2)) or endogenously expressed amidase were localized exclusively at the cross-wall region, while in Delta tagO mutant that lacks WTA binding was evenly distributed on the cell surface, which explains the increased fragility and autolysis susceptibility of the mutant. WTA prevented binding of Atl to the old cell wall but not to the cross-wall region suggesting a lower WTA content. In binding studies with ConcanavalinA-fluorescein (ConA-FITC) conjugate that binds preferentially to teichoic acids, ConA-FITC was bound throughout the cell surface with the exception of the cross wall. ConA binding suggest that either content or polymerization of WTA gradually increases with distance from the cross-wall. By preventing binding of Atl, WTA directs Atl to the cross-wall to perform the last step of cell division, namely separation of the daughter cells.