The N-Terminal Flanking Region Modulates the Actin Binding Affinity of the Utrophin Tandem Calponin-Homology Domain

Despite sharing a high degree of sequence similarity, the tandem calponin-homology (CH) domain of utrophin binds to actin 30 times stronger than that of dystrophin. We have previously shown that this difference in actin binding affinity could not be ascribed to the differences in inter-CH-domain linkers [Bandi, S., et al. (2015) Biochemistry 54, 5480–5488]. Here, we examined the role of the N-terminal flanking region. The utrophin tandem CH domain contains a 27-residue flanking region before its CH1 domain. We examined its effect by comparing the structure and function of full-length utrophin tandem CH domain Utr(1–261) and its truncated Utr(28–261) construct. Both full-length and truncated constructs are monomers in solution, with no significant differences in their secondary or tertiary structures. Truncated construct Utr(28–261) binds to actin 30 times weaker than that of the full-length Utr(1–261), similar to that of the dystrophin tandem CH domain with a much shorter flanking region. Deletion of the ...