Oligomer Assembly of the C-Terminal DISC1 Domain (640-854) Is Controlled by Self-Association Motifs and Disease-Associated Polymorphism S704C

Genetic studies have established a role of disrupted-in-schizophrenia-1 (DISCI) in chronic mental diseases (CMD). Limited experimental data are available on the domain structure of the DISC I protein although multiple interaction partners are known including a self-association domain within the middle part of DISC1 (residues 403-504). The DISC1 C-terminal domain is deleted in the original Scottish pedigree where DISCI harbors two coiled-coil domains and disease-associated polymorphisms at 607 and 704, as well as the important nuclear distribution element-like I (NDEL1) binding site at residues 802-839. Here, we performed mutagenesis Studies of the C-terminal domain of the DISCI protein (residues 640-854) and analyzed the expressed constructs by biochemical and biophysical methods. We identified novel DISCI self-association motifs and the necessity of their concerted action for orderly assembly: the region 765-854 comprising a coiled-coil domain is a dimerization domain and the region 668-747 an oligomerization domain; dimerization was found to be a prerequisite for orderly assembly of oligomers. Consistent with this, disease-associated polymorphism C704 displayed a slightly higher oligomerization propensity. The heterogeneity of DISC1 multimers in vitro was confirmed with a monoclonal antibody binding exclusively to HMW multimers. We also identified C-terminal DISCI fragments in human brains, suggesting that C-terminal fragments could carry out DISC1-dependent functions. When the DISC1 C-terminal domain was transiently expressed in cells, it assembled into a range of soluble and insoluble multimers with distinct fractions selectively binding NDEL1, indicating functionality. Our results suggest that assembly or the C-terminal domain is controlled by distinct domains including the disease-associated polymorphism 704 and is functional in. vivo.