Fig. 1: Size distribution and secondary structure composition of DISC1 C-region oligomers.

A Pictorial representation of the primary structure of the DISC1; the D, I, S and C regions and the potential binding-partner interaction sites are annotated. For more details, the reader is referred to reviews in references [3,4,5, 8, 9, and 14]. The lower panel shows the C-region with the V_HH B5 nanobody-binding site (magenta), the (pseudo)repeat sequence (orange), and the C-terminal NDEL1-binding site (green); the region missing in the Δ22 variant is indicated by a dotted box. The same color-coding scheme is also used in the structural model in Fig. 4D. Post-translational modification and mutation sites have been annotated for the C-region. B DLS measurements on the His₆-tagged version at 37 °C, using various concentrations: 10 µM (green, apparent hydrodynamic radius (R_H): 4.1 nm ± 0.7 nm, calculated molecular mass (M): 81.5 kDa), 20 µM (brown, R_H: 4 ± 0.6 nm, M: 81.3 kDa), 30 µM (yellow, R_H: 4.1 ± 0.5 nm, M: 84 kDa), 40 µM (sky blue, R_H: 4.4 ± 0.5 nm, M: 87 kDa; R_H: 17.2 ± 3.6 nm, M: 2.3 MDa; R_H: 18.9 ± 4.4 nm, M: 2.8 MDa), and 90 µM (magenta, R_H: 4.1 ± 0.6 nm, M: 85.7 kDa; R_H: 13 ± 2.5 nm, M: 1.2 MDa). The estimated molecular mass of the smallest species is suggestive of a tetramer. While the top panel illustrates the time-dependent evolution of the radius distribution, the bottom panel displays histograms derived from the entire data set. C In order to further characterize the oligomerization process of the C-region and the accompanying structural changes, we performed DLS measurements (top panel) along with CD spectroscopy (bottom panel) at various temperatures, 20 °C (black), 30 °C (red), 37 °C (orange), 45 °C (green), 50 °C (blue), and 60 °C (cyan). One additional spectrum (yellow) represents the CD profile of the freshly prepared sample.