Phosphorylation-Dependent Mobility Shift of Proteins on SDS-PAGE is Due to Decreased Binding of SDS

While many eukaryotic and some prokaryotic proteins show a phosphorylation-dependent mobility shift (PDMS) on SDS-PAGE, the molecular mechanism for this phenomenon had not been elucidated. We have recently shown that the distribution of negatively charged amino acids around the phosphorylation site is important for the PDMS of some proteins. Here, we show that replacement of the phosphorylation site with a negatively charged amino acid results in a similar degree of the mobility shift of a protein as phosphorylation, indicating that the PDMS is due to the introduction of a negative charge by phosphorylation. Compared with a protein showing no shift, one showing a retarded mobility on SDS-PAGE had a decreased capacity for SDS binding. The elucidation of the consensus sequence (ΘX1-3ΘX1-3Θ, where Θ corresponds to an acidic function) for a PDMS suggests a general strategy for mutagenizing a phosphorylatable protein resulting in a PDMS.