A pachygyria-causing alpha-tubulin mutation results in inefficient cycling with CCT and a deficient interaction with TBCB.
The agyria (lissencephaly)/pachygyria phenotypes are catastrophic developmental diseases characterized by abnormal folds on the surface of the brain and disorganized cortical layering. In addition to mutations in at least four genes--LIS1, DCX, ARX and RELN--mutations in a human alpha-tubulin gene, TUBA1A, have recently been identified that cause these diseases. Here, we show that one such mutation, R264C, leads to a diminished capacity of de novo tubulin heterodimer formation. We identify the mechanisms that contribute to this defect. First, there is a reduced efficiency whereby quasinative alpha-tubulin folding intermediates are generated via ATP-dependent interaction with the cytosolic chaperonin CCT. Second, there is a failure of CCT-generated folding intermediates to stably interact with TBCB, one of the five tubulin chaperones (TBCA-E) that participate in the pathway leading to the de novo assembly of the tubulin heterodimer. We describe the behavior of the R264C mutation in terms of its effect on the structural integrity of alpha-tubulin and its interaction with TBCB. In spite of its compromised folding efficiency, R264C molecules that do productively assemble into heterodimers are capable of copolymerizing into dynamic microtubules in vivo. The diminished production of TUBA1A tubulin in R264C individuals is consistent with haploinsufficiency as a cause of the disease phenotype.
Tian
Guoling
G
Department of Biochemistry, New York University Medical Center, New York, NY 10016, USA.
Kong
Xiang-Peng
XP
Jaglin
Xavier H
XH
Chelly
Jamel
J
Keays
David
D
Cowan
Nicholas J
NJ
D000818:Animals; D002417:Cattle; D056404:Chaperonin Containing TCP-1; D018833:Chaperonins / Q000378:metabolism*; D019281:Dimerization; D006160:Guanosine Triphosphate / Q000378:metabolism; D006367:HeLa Cells; D006801:Humans; D054082:Lissencephaly / Q000235:genetics*; D008869:Microtubule-Associated Proteins / Q000378:metabolism*; D008870:Microtubules / Q000378:metabolism; D050505:Mutant Proteins / Q000378:metabolism; D009154:Mutation / Q000235:genetics*; D011485:Protein Binding; D011499:Protein Processing, Post-Translational; D017434:Protein Structure, Tertiary; D000091042:Reelin Protein; D014158:Transcription, Genetic; D014404:Tubulin / Q000737:chemistry / Q000235:genetics*
D008869:Microtubule-Associated Proteins; D050505:Mutant Proteins; D000091042:Reelin Protein; D014404:Tubulin; D006160:Guanosine Triphosphate; C000717127:RELN protein, human; D056404:Chaperonin Containing TCP-1; D018833:Chaperonins