Towards monitoring of protein purification by matrix-assisted laser desorption ionization mass spectrometry

Abstract

The purpose of the present study is to investigate if Matrix-Assisted Laser Desorption Ionization (MALDI) Mass Spectrometry (MS) can be used as a general method for monitoring protein purification procedures. With this aim, the compatibility of MALDI/MS with protein samples containing various buffers, salts and detergents commonly used in protein purification is examined. The pH value of the sample during the crystallization process is found to be the critical point. As long as the pH value is kept below 2 by the addition of sufficiently concentrated trifluoroacetic acid (TFA), spectra can be obtained from solutions containing high concentrations of buffer or salts and up to 0.2% of sodium dodecyl sulfate (SDS). Reference spectra can be obtained by MALDI/MS of proteins electroeluted from electrophoretic gels as demonstrated using 2D-PAGE and further specificity obtained by preparing mass spectrometric peptide maps from the eluate. The value of the concept is demonstrated by relating the proteins purified from an extract of meal worm cuticle proteins with 2D-PAGE of the total extract. Finally a general strategy for monitoring protein purification by MALDI/MS is outlined and discussed.