MATRIX-ASSISTED LASER DESORPTION/IONIZATION MASS-SPECTROMETRY (MALDI-MS) OF MEMBRANE-PROTEINS AND NONCOVALENT COMPLEXES

Matrix-assisted laser desorption/ionization (MALDI) mass spectra and methods to improve their quality are reported for three hydrophobic, membrane-bound proteins: porin from Escherichia coli, bacteriorhodopsin from Halobacterium salinarium and cholesterolesterase from Pseudomonas fluorescens. Several commonly used UV and IR matrices have been tested. In addition, the susceptibility of MALDI mass spectrometry to various neutral and ionic detergents, known usually to degrade the quality of MALDI mass spectra, has been tested systematically, For porin, consisting of three identical non-covalently bound subunits, a new sample preparation is reported, resulting in the desorption of the intact quaternary protein structure. This leads to a better understanding of the way a given analyte is embedded into the host matrix crystals.