Diversity of puroindolines as revealed by two-dimensional electrophoresis

Puroindolines are endosperm lipid binding proteins, which are separated by reversed phase-high-performance liquid chromatography or cation exchange chromatography into two isoforms, puroindoline-a (PIN-a) and puroindoline-b (PIN-b). Being very basic and close in molecular weight, PIN-a and PIN-b have never been separated using conventional isoelectric focusing and sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). A two-dimensional electrophoresis method, linear immobiline pH gradient (IPG x SDS-PAGE), was developed, using 6-11 linear immobiline Dry Strips in the first dimension, which allowed the puroindolines to be focused between isoelectric point 10.5 and 11. Immunoblotting revealed that both PIN-a and PIN-b were each composed of several spots. Two-dimensional patterns from unrelated wheat varieties revealed that several spots can be highlighted among varieties. Matrix-assisted laser desorption/ionization-time of flight spectrometry allowed the majority of the spots revealed in the puroindoline zone to be identified. The two-dimensional IPG x SDS-PAGE of these very basic wheat endosperm proteins, puroindolines and related grain softness proteins should facilitate the identification of the proteins associated with wheat endosperm texture that have a strong effect on milling, dough properties and end-uses of wheats.