Patient mutations in doublecortin define a repeated tubulin-binding domain.
Doublecortin (DCX) missense mutations are found in two clusters in patients with defective cortical neuronal migration. Although DCX can function as a microtubule-associated protein (MAP), the potential relationship between its MAP activity and neuronal migration is not understood. Here we show that the two clusters of patient mutations precisely define an internal tandem repeat. Each repeat alone binds tubulin, whereas neither repeat is sufficient for co-assembly with microtubules. The two tandem repeats are sufficient to mediate microtubule polymerization, and representative patient missense mutations lead to impaired polymerization both in vitro and in vivo as well as impaired microtubule stabilization. Furthermore, each repeat is predicted to have the secondary structure of a beta-grasp superfold motif, a motif not found in other MAPs. The patient mutations are predicted to disrupt the structure of the motif, suggesting that the motif may be critical for the DCX-tubulin interaction. These data provide both genetic and biochemical evidence that the interaction of DCX with microtubules is dependent upon this novel repeated tubulin-binding motif.
Taylor
K R
KR
Division Pediatric Neurology, Department of Neurosciences, Biomedical Sciences Graduate Program, University of California, San Diego, La Jolla, California 92093, USA.
Holzer
A K
AK
Bazan
J F
JF
Walsh
C A
CA
Gleeson
J G
JG
D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D001665:Binding Sites; D001704:Biopolymers; D019556:COS Cells; D002465:Cell Movement / Q000235:genetics; D017931:DNA Primers; D000089622:Doublecortin Domain Proteins; D000089662:Doublecortin Protein; D006801:Humans; D008869:Microtubule-Associated Proteins; D008969:Molecular Sequence Data; D020125:Mutation, Missense; D009474:Neurons / Q000166:cytology; D009479:Neuropeptides / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D017510:Protein Folding; D017386:Sequence Homology, Amino Acid; D020080:Tandem Repeat Sequences; D014404:Tubulin / Q000378:metabolism*
D001704:Biopolymers; C000714328:DCX protein, human; D017931:DNA Primers; D000089622:Doublecortin Domain Proteins; D000089662:Doublecortin Protein; D008869:Microtubule-Associated Proteins; D009479:Neuropeptides; D014404:Tubulin