Figure 4. Structural effects of SSBP1 mutations.

(A) Crystal structure of SSBP1 showing that human SSBP1 consists of a dimer (molecules molA and molB) that contacts a second, symmetrically related dimer (molA′ and molB′), giving rise to the tetrameric biological unit. Both Arg38 and Arg107 are displayed in yellow (frame). (B) Zoom-in of mutated residues; Arg38 is replaced by Gln38 (top). The bottom panel is the same, except Arg107 is replaced by Gln 107. In each case, the mutated residue is shown in light gray. (C) SDS/PAGE analysis of SSBP1 monomers and dimers in control (control 1 and control 2) and patient fibroblasts (patient 1, patient 2, patient 3). Actin was used as a loading control. For each cell line, 3 independent biological replicates were loaded. (D) Densitometric quantification of SSBP1 monomer (left) and dimer (right) in pooled controls and patient fibroblasts. Data are shown as scatter plots with mean ± SEM indicated. **P < 0.01; ***P < 0.001, 1-way ANOVA with Dunnett’s correction. Note that some of the same samples (for control 1, patient 1, and patient 2) were run on both membranes and these thus represent technical replicates. The ratios with actin from both membranes were averaged prior to statistical analysis.