Has a role in the regulation of microfilament formation. Phosphorylates the actin-fragmin complex on threonine residues, in vitro. ATP + L-seryl-[protein] = ADP + H(+) + O-phospho-L-seryl-[protein] ATP + L-threonyl-[protein] = ADP + H(+) + O-phospho-L-threonyl-[protein] Inhibited by staurosporine. Monomer. Belongs to the protein kinase superfamily. AFK protein kinase family.