Identification of pneumococcal proteins that are functionally linked to penicillin-binding protein 2b (PBP2b).

The oval shape of pneumococci results from a combination of septal and lateral peptidoglycan synthesis. The septal cross-wall is synthesized by the divisome, while the elongasome drives cell elongation by inserting new peptidoglycan into the lateral cell wall. Each of these molecular machines contains penicillin-binding proteins (PBPs), which catalyze the final stages of peptidoglycan synthesis, plus a number of accessory proteins. Much effort has been made to identify these accessory proteins and determine their function. In the present paper we have used a novel approach to identify members of the pneumococcal elongasome that are functionally closely linked to PBP2b. We discovered that cells depleted in PBP2b, a key component of the elongasome, display several distinct phenotypic traits. We searched for proteins that, when depleted or deleted, display the same phenotypic changes. Four proteins, RodA, MreD, DivIVA and Spr0777, were identified by this approach. Together with PBP2b these proteins are essential for the normal function of the elongasome. Furthermore, our findings suggest that DivIVA, which was previously assigned as a divisomal protein, is required to correctly localize the elongasome at the negatively curved membrane region between the septal and lateral cell wall.