Detection of protein phosphorylation and charge isoforms using vertical one-dimensional isoelectric focusing gels

pI Determination of Native Proteins In Biological Samples

The electrophoretic mobility of a protein on an immobilized pH-gradient gel (IPG) depends upon its overall positive (acidic) or negative (basic) charge, the principle underlying the IEF technique. In isoelectrofocusing (IEF), a protein with a net positive or negative charge migrates through the pH gradient gel until it reaches the isoelectric point (pI), a pH at which it remains neutral. Thus, the pI of a protein indicates its net charge, a critical determinant of its stability/activity in a given milieu. Conventionally, the first-dimensional IPG-IEF is followed by a second dimension, by which the focused proteins are denatured/reduced and resolved on an SDS-PAGE gel for subsequent immunoblotting to verify the protein identity. The recent development of one-dimensional, vertical IEF followed by immunoblotting enabled concurrent analysis (pI determination) of multiple samples. The protocol described here outlines vertical IEF and immunoblotting under non-denaturing conditions to determine the pI of native proteins in biological samples. © 2019 by John Wiley & Sons, Inc.

Monitoring protein phosphorylation by acrylamide pendant Phos-Tag™ in various plants

The aim of the present study is to rationalize acrylamide pendant Phos-Tag™ in-gel discrimination of phosphorylated and non-phosphorylated plant protein species with standard immunoblot analysis, and optimize sample preparation, efficient electrophoretic separation and transfer. We tested variants of the method including extraction buffers suitable for preservation of phosphorylated protein species in crude extracts from plants and we addressed the importance of the cation (Mn(2+) or Zn(2+)) used in the gel recipe for efficient transfer to PVDF membranes for further immunoblot analysis. We demonstrate the monitoring of Medicago sativa stress-induced mitogen activated protein kinase (SIMK) in stress-treated wild type plants and transgenic SIMKK RNAi line. We further show the hyperosmotically-induced phosphorylation of the previously uncharacterized HvMPK4 of barley. The method is validated using inducible phosphorylation of barley and wheat α-tubulin and of Arabidopsis MPK6. Acrylamide pendant Phos-Tag™offers a flexible tool for studying protein phosphorylation in crops and Arabidopsis circumventing radioactive labeling and the use of phosphorylation specific antibodies.