Phos-tag diagonal electrophoresis precisely detects the mobility change of phosphoproteins in Phos-tag SDS-PAGE

Phos-tag diagonal electrophoresis was developed to identify precisely a change in electrophoretic mobility of phosphoproteins in Phos-tag SDS-PAGE. Previously, if a single protein band was detected, it was impossible to determine whether mobility of the protein altered by Mn²⁺ Phos-tag in Phos-tag SDS-PAGE gels because SDS-PAGE and Phos-tag SDS-PAGE were performed on different gels. Moreover, when multiple protein bands were detected, it was difficult to determine whether the band with the highest mobility was altered mobility by Mn²⁺ Phos-tag. However, these problems were resolved by Phos-tag diagonal electrophoresis in which SDS-PAGE and Phos-tag SDS-PAGE patterns were provided on a single gel. Using this technique we identified phosphorylation states of various proteins such as α-lactalbumin, α- and β-casein, ovalbumin, basic 7S globulin, and 26S proteasome subunits. In the analyses of 26S proteasome subunits from humans and yeast, we could confirm that all subunits are phosphorylated, and find that the number of major proteins with different phosphorylation states is a few in each of the subunits despite having many phosphorylation sites. SIGNIFICANCE: Previously, Phos-tag SDS-PAGE has been developed to identify a change in electrophoretic mobility of phosphoproteins. However, we had a problem in this technique; it was often difficult to recognize the mobility shift by Mn²⁺ Phos-tag when we used separately SDS-PAGE and Phos-tag SDS-PAGE. Such a problem was resolved by Phos-tag diagonal electrophoresis in which SDS-PAGE and Phos-tag SDS-PAGE patterns are provided on a single gel. This technique was useful to identify phosphorylation states of various proteins. : Phos-tag diagonal electrophoresis, mass spectrometry, phosphoproteins, basic 7S globulin, proteasome.