Protein kinase involved in signal transduction pathways that regulate various cellular processes. Likely senses intracellular peptidoglycan subunits present in the cell division septa of actively growing cells; thus, intracellular unlinked peptidoglycan may serve as the signal molecules that trigger StkP phosphorylation activity on a set of substrates. Plays a crucial role in the regulation of cell shape and cell division of S.pneumoniae through control of at least DivIVA activity. Is involved in competence triggering, and is required for the expression of the central competence operon comCDE. StkP also plays an important role for bacterial survival in vivo. Identified target substrates that are specifically phosphorylated by StkP in vivo, mainly on threonine residues, are DivIVA, GlmM, PpaC, MapZ, KhpB (also called EloR/Jag, shown in strains R6 and Rx1) and StkP itself. Autophosphorylated StkP is a substrate for the cotranscribed protein phosphatase PhpP (shown in the avirulent strain Rx / Cp1015); PhpP and StkP appear to constitute a functional signaling couple in vivo. ATP + L-seryl-[protein] = ADP + H(+) + O-phospho-L-seryl-[protein] ATP + L-threonyl-[protein] = ADP + H(+) + O-phospho-L-threonyl-[protein] Homodimer. StkP forms dimers through its transmembrane and extracellular domains. Dimer formation likely promotes autophosphorylation activity and might be necessary for targeting StkP substrate (By similarity). Localizes to the midcell division sites, colocalizes with PBP2b. Consists of an N-terminal kinase domain, a transmembrane domain, and a C-terminal domain containing four repeats of the PASTA signature sequence (Penicillin-binding protein and Ser/Thr protein kinase associated domain). The PASTA domain binds to peptidoglycan (PGN) subunits, is essential for StkP activation and substrate phosphorylation (shown in the avirulent strain Rx / Cp1015), and is responsible for cellular targeting to midcell. Autophosphorylation occurs predominantly at the threonine residue and weakly at the serine residue. Dephosphorylated by PhpP (By similarity). Disruption of stkP gene results in strong repression of competence development for genetic transformation in vitro. Strains D39 (serotype 2) and 23477 (serotype 6) lacking this gene show a greatly attenuated virulence in lung infection and bloodstream invasion in mice, but no in vitro growth defect. PubMed:20453092 shows that the patterns of phosphorylated proteins are similar for S.pneumoniae Rx / Cp1015 and D39 (avirulent and virulent strains, respectively) when they are grown in complex CAT medium. Thus, in both strains, StkP phosphorylates the same set of substrates that are probably important for sustaining normal growth in laboratory conditions. Belongs to the protein kinase superfamily. Ser/Thr protein kinase family.