Supplementary Figure 5: Screening for additives.

Analysis of Biomphalaria glabrata hemoglobin complex (BgHb, 1.5 MDa native molecular weight) – a protein of unknown structure. Under standard purification conditions BgHb is mostly present as aggregated particles in negatively stained EM images (left panel, scale bar = 50 nm). The upper pane of the middle panel depicts a subset of unfolding transitions from a ProteoPlex pH screen. The stability of BgHb is gradually increased from alkaline to acidic Imidazole buffer conditions, with a final enhanced stabilization of 45 K at pH 5.8 compared to pH 8.2. The lower pane of the middle panel reveals that interpretable unfolding transitions of the complex only occurs in Imidazole buffer, which suggests the role of Imidazole additionally as a stabilizing ligand. In Imidazole pH 5.8, negatively stained EM analysis reveals a monodisperse field of compact particles (right panel, scale bar 50 nm).