Fig 6.

SOS1's allosteric pocket is dispensable for optimal p38 activation. (A, B, and C) W729E hSOS1 and WT hSOS1 similarly rescue the SOS1⁻ SOS2⁻ DT40 cells in terms of p38 activation regardless of stimulus dosage. Quantitation of pERK and phospho-p38 signals relative to the maximum WT control level is plotted in panel C. Note that the ERK activation defect in W729E hSOS1-reconstituted cells is most noticeable with low anti-BCR stimulation. (D) p38 activation at 10 min of stimulation is measured in response to a 2-fold serial dilution of anti-BCR antibody at a range of intermediate dosages. (E) SOS1⁻ SOS2⁻ DT40 cells were transiently transfected with empty vector, WT hSOS1, or W729E hSOS1 and stimulated as indicated. Transfected cells were magnetically purified by positive selection of cotransfected human CD16/7 fusion protein. Numbers for phospho-ERK and -p38 are generated by taking the ratios of pERK/ERK and phospho-p38/p38 in the individual samples and setting the maximum phosphoprotein level in the wild-type control to 100%. Representative blots of at least three experiments.