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Catalytic domain of Actin-Fragmin Kinase AFK is found in slime molds, ciliates, and flowering plants. It catalyzes the transfer of the gamma-phosphoryl group from ATP specifically to threonine residues in the actin-fragmin complex. The phosphorylation sites are located at a minor contact site for DNase I and at an actin-actin contact site. Fragmin is an actin-binding protein that functions as a regulator of the microfilament system. It interferes with the growth of F-actin by severing actin filaments and capping their ends. The phosphorylation of the actin-fragmin complex inhibits its nucleation activity and results in calcium-dependent capping activity. Thus, AFK plays a role in regulating actin polymerization. The AFK catalytic domain is part of a larger superfamily that includes the catalytic domains of other kinases such as the typical serine/threonine/tyrosine protein kinases (PKs), RIO kinases, aminoglycoside phosphotransferase, choline kinase, and phosphoinositide 3-kinase.
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Jiyao W et al.(2023). "The conserved domain database in 2023.",