Gel filtration of mixtures of Spβ1898-2083 and SpαArg28/Arg45, Arg28Ser, Arg45Ser, or Arg45Thr at 7 μM.

The top 2 chromatograms of the individual sample are shown as references; additional measurements were done at 12 and 30 μM (data not shown). The position of each species is indicated by an arrow on the top chromatogram. We used 5 mM phosphate buffer with 150 mM NaCl at pH 6.5 (NMR sample buffer) for sample incubation and as eluting buffer. Schematic representations of the native Spα1-156 and Spβ1898-2083 structures are shown as insets above the corresponding chromatograms. The positions of the Arg28 and Arg45 mutations are shown by addition of the side chains at their sequence positions in insets above the corresponding chromatograms.