Protein kinase which regulates actin filament dynamics. Phosphorylates and inactivates the actin binding/depolymerizing factor cofilin, thereby stabilizing the actin cytoskeleton. Required for motility of the axon growth cone. ATP + L-seryl-[protein] = ADP + H(+) + O-phospho-L-seryl-[protein] ATP + L-threonyl-[protein] = ADP + H(+) + O-phospho-L-threonyl-[protein] Recruited to axon growth cones. Expressed predominantly in the brain. Belongs to the protein kinase superfamily. TKL Ser/Thr protein kinase family.