Isoelectric focusing in serial immobilized pH gradient gels to improve protein separation in proteomic analysis

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Abstract
We previously demonstrated the separation of proteins by isoelectric focusing (IEF) over pH 4–8 immobilized pH gradients (IPGs) over 54 cm (Poland et al., Electrophoresis 2003, 24, 1271). Here we show that similar results can be conveniently achieved using commercially available IPGs of appropriate pH ranges positioned end‐on‐end in series during electrophoresis, which we term ‘daisy chain IEF’. Proteins efficiently electrophorese from one IPG to another during IEF by traversing buffer‐filled porous bridges between the serial IPGs. A variety of materials can function as bridges, including paper, polyacrylamide gels or even IPGs. The quality of two‐dimensional (2‐D) protein patterns is not apparently worse than that generated by conventional IEF using the same individual IPGs. A major advantage of this method is that sample is consumed efficiently, without the requirement for preliminary steps, such as chamber IEF. This advantage is pronounced when working with extremely limited sources of samples, such as with clinical biopsies or cellular subfractions. The present study was limited by the commercial availability of suitable pH gradients. Proteomics analyses could be further improved if commercial vendors would manufacture IPGs with suitable pH ranges to achieve high resolution (∼100 cm) IEF separation of proteins in one electrophoretic step over the pH range 2–12.