SPG3: Towards Understanding the Function of the Disease Protein Atlastin 1

Approximately 10% of all autosomal dominant spastic paraplegia cases are caused by mutations in the large GTPase atlastin 1. Atlastin 1 is a 558 aa transmembrane protein localized to the Golgi apparatus with both the large N-terminal GTPase domain and the short C-terminus being directed towards the cytoplasm. To date 19 missense mutations distributed throughout the protein and one frameshift mutation have been identified, yet the function of atlastin 1 in motoneurons and the disease mechanism are still poorly understood. For this reason we are interested in 1) identifying physiological interactors of atlastin; 2) the influence of different mutations on the enzyme activity and guanine nucleotide affinity of this enzyme. In a Y2H screen with the 63 aa long C-terminal domain we have identified a weak interactor, which is possibly involved in neuronal mRNA processing. Besides a similar expression profile, our confocal microscopy studies in cos-7 cells transfected with HA-tagged atlastin showed partial colocalization of atlastin 1 with this endogeneously expressed interactor in the Golgi apparatus. We also have purified both wildtype and mutated atlastin 1 as GST fusion protein, and will present preliminary data on GTP hydrolysis and binding assays performed in a collaborative effort.