Contrasting sites between ROPK and PK: C-lobe WC motif and loss of Glu constraint. (A) and (B) Structures of ROP2 and ROP5 with WC motif and ROPK-conserved disulfide bridge residues shown in “sticks” representation. (C) Sequence logos of F helix region in ROPK (top) and ePK (bottom), with contrasting sites highlighted. (D) PKA, a representative typical protein kinase, with equivalent residues shown as sticks. (E) CDK2, another typical protein kinase. The “CMGC insert” occurs in the α G–αH loop but does not perform the same structural role as the ROPK-specific insert in the same region.