Figure 1

Analysis of the oligomeric state of the p15-His protein. (A) DLS spectrogram obtained with the p15-His protein at 3 and 6 mg/ml in 50 mM sodium phosphate pH 7.4 buffer (left curves) and 50 mM MES pH 6 buffer (right curves), respectively. (B) Chemical cross-linking with BS³ of p15 with or without 6-His tag. Lanes 1 to 4: p15-His at-3.3 and 3 mg/ml (lane 1 and 2) or 6 and 6.5 mg/ml (lane 3 and 4), in 50 mM MES pH 6 buffer (lane 1 and 3) and 50 mM sodium phosphate pH 7.4 buffer (lane 2 and 4). Lanes 5 and 6: p15 without 6-His tag at 6 mg/ml in 50 mM sodium phosphate pH 7.4 buffer (lane 5) or 50 mM MES pH 6 buffer (lane 6). M is the molecular weight marker. The asterisk indicates the expected size for the dimeric form. (C) The SEC-MALLS spectra of the molecular weight (dotted line) and absorbance at 280 nm (plain lines) versus elution volume. The p15 protein in 50 mM MES pH 6 buffer and at 6 mg/ml was loaded into the column. (D) Dissociation constant of the p15-His dimer measured by ITC. The thermogram (top panel) and the plotted titration curve (bottom panel) were obtained with a Microcal ITC200. The solid line (bottom panel) represents the fitting of the data by the built-in dimer dissociation model.