Influence of Ser/Pro-rich domain and kinase domain of double cortin-like protein kinase on microtubule-binding activity

Doublecortin-like protein kinase (DCLK) is a Ser/Thr protein kinase predominantly expressed in brain. DCLK is composed of three functional domains; the N-terminal doublecortin-like (DC) domain, the C-terminal kinase domain and Ser/Pro-rich (SP) domain in between DC and kinase domains. Although the DC domain is known to mediate microtubule association, functional roles of the SP domain and the kinase domain on microtubule association is not known. In this study, we investigated the microtubule-binding activity of zebrafish DCLK (zDCLK) using various deletion mutants and chimeric proteins. The microtubule-binding activity of various mutants of zDCLK was assessed both by immunocytochemical analysis and by biochemical analysis using detergent extraction method. When the kinase domain was removed from zDCLK, the microtubule-binding activity was significantly enhanced. Although the zDCLK(DC + SP) mutant showed a strong microtubule-binding activity, the DC domain alone showed much lower microtubule-binding activity, indicating that the SP domain of zDCLK plays a role in enhancing microtubule-binding activity of the DC domain. These results suggest that both the kinase domain and the SP domain are involved in regulating the microtubule-binding activity of DCLK.