Addition of carboxy terminal myc-tag to profilin IIa dramatically reduces poly(L-proline) binding. A. Biacore binding curves for 100 μM wild type profilin IIa (blue), 1 μM wild type profilin IIa (green), or 100 μM profilin IIa-myc (red) to the (GP5)3 peptide derived from VASP. Resonance units (R.U.) are a measure for the number of profilin molecules retained by the peptide on the sensor chip and this is also concentration dependent (see B.). Even at a 100 times higher concentration, profilin IIa-myc (100 μM) binds less efficient to the peptide than wild type profilin IIa (1 μM). B. R.U. values obtained with different concentrations of wild type profilin IIa and profilin IIa-myc. Note that the value for 100 μM wild type profilin IIa is different from the one in Table 1, due to a different amount of peptide coupled to the sensor chip.