Gigaxonin is associated with the Golgi and dimerises via its BTB domain

Mutations in the gigaxonin gene cause giant axonal neuropathy. The amino-terminus of gigaxonin contains a BTB domain but no binding partners for this domain have so far been identified. Here, we demonstrate that the gigaxonin BTB domain forms homodimers. Other BTB-bearing proteins have also been shown to dimerise via their BTB domains with the dimers then capable of interacting with other ligands. Thus, the gigaxonin BTB domain may function in a similar manner. We also demonstrate that gigaxonin is expressed in a wide variety of neuronal cell types where a significant proportion exists in cell bodies. Confocal microscope studies of gigaxonin-transfected COS-7 cells and cultured neurones revealed that a proportion of gigaxonin localises to the Golgi and endoplasmic reticulum.