Members of this family assume a secondary structure consisting of eight beta strands and 11 alpha-helices, organised in two lobes. They are predominantly found in actin-fragmin kinase, where they act as a catalytic domain that mediates the phosphorylation of actin [1].

1: The crystal structure of the Physarum polycephalum actin-fragmin kinase: an atypical protein kinase with a specialized substrate-binding domain. Steinbacher S, Hof P, Eichinger L, Schleicher M, Gettemans J, Vandekerckhove J, Huber R, Benz J; EMBO J. 1999;18:2923-2929. PMID:10357805