The eSTKs regulate streptococcal peptidoglycan synthesis with distinct subcellular localizations and coordination with Pbps in S. suis and S. pneumoniae

Abstract Compared with traditional drugs targeting penicillin-binding proteins (Pbps), targeting the upstream coordinators of bacterial peptidoglycan (PG) synthesis is a highly promising strategy for overcoming the frequent occurrence of resistance to β-lactam drugs. Eukaryotic-like serine/threonine kinases (eSTKs) are core coordinators of bacterial cell division and PG synthesis in many pathogenic bacteria, and their activity is exemplified in the well-studied ovoid bacterium Streptococcus pneumoniae . Here, we demonstrate that eSTK activity in Streptococcus suis (STKss), another ovoid bacterium, is crucial for the normal cell division cycle and morphology, especially in septum formation. The abnormalities observed during the cell division cycle in S. suis mutants were similar in both the S. pneumoniae STK (STKsp) mutant and the kinase activity-deficient mutant. However, orthologous eSTKs in these two species failed to functionally replace each other in reciprocal complementation assays. STKss and STKsp localization experiments in wild-type and mutant strains, including the replacement of different domains of the two eSTKs, revealed that incompatibility stemmed from their divergent localization patterns during the cell cycle, which were primarily dictated by their extracellular PASTA4 domains. During septal PG synthesis, STKss and STKsp consistently localized to the inner and outer edges of the septum, respectively. Additionally, both STKss and STKsp interact with similar PG synthesis and remodeling proteins, with differences in their spatial coordination with the core PG synthases Pbp2B (peripheral synthesis) and Pbp2X (septal synthesis). Collectively, these findings indicate that diverse eSTK localizations are directed by the PASTA4 domain and coordination with Pbps during the regulation of cell division among closely related ovoid bacteria. Given the essentiality of eSTKs in governing the growth, metabolism and virulence of various species of pathogenic bacteria, eSTKs have become promising drug targets for the development of novel antibacterial agents .