| Abstract
| - Doublecortin kinase-1 (DCK1) is a newly described multidomain protein kinase with a sequencesignificantly similar to those of both CaM kinases (CaMKs) and doublecortin, the product of the genemutated in X-linked lissencephaly/double cortex syndome, a severe developmental disorder of the nervoussystem. Functional studies have revealed microtubule binding and polymerization activities of thedoublecortin domain, yet little is known regarding the enzymatic properties and regulation of the kinasecatalytic domain. We have identified and report here notable similarities as well as differences betweenthe catalytic and regulatory properties of DCK1 and those of the CaMKs. Using synthetic peptide substratesmodeled on synapsin I, a substrate recognition motif for DCK1 of Hyd-Arg-Arg-X-X-Ser*/Thr*-Hydwas derived. The similarity of this motif to that of CaMKI [Lee, J. C., Kwon, Y.-G., Lawrence, D. S.,and Edelman, A. M. (1994) Proc. Natl. Acad. Sci.U.S.A.91, 6413−6417] is consistent with the 59%level of amino acid sequence similarity between their catalytic domains. DCK1 catalytic activity is enhancedby mutagenic introduction of negative charge at Thr-239, a residue in a position equivalent to that ofThr-177 of CaMKI, the activation loop site for regulation by CaM kinase kinase. Unlike CaMKs, DCK1is not directly activated by Ca2+-bound CaM. However, truncation of a pseudosubstrate-like sequence inthe C-terminus of DCK1 results in an ∼6-fold enhancement of activity. Thus, DCK1 demonstrates thepotential to be regulated by relief of autoinhibition in response to signal(s) distinct from Ca2+-boundCaM and potentially by activation loop phosphorylation and to phosphorylate intracellular targets at sitessimilar to those recognized by CaMK pathways.
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