MONITORING PROTEIN EXPRESSION IN WHOLE BACTERIAL-CELLS WITH MALDI TIME-OF-FLIGHT MASS-SPECTROMETRY

We report the application of matrix-assisted laser desorption ionizati on (MALDI) to monitor recombinant protein expression in whole bacteria . This technique is characterized by rapid sample preparation that pro vides analysis of samples extracted directly from the growth media in less than 10 min. The mass spectrometric method holds several advantag es over gel electrophoresis, the conventional method for examining the protein content of cells. Comparisons between the two methods of anal ysis are presented in terms of increased speed, efficiency, resolution , and mass accuracy. Delayed extraction time-of-flight mass spectromet ry identifies posttranslational modifications and other changes in the expected structure which are not recognized by gel electrophoresis. T he utility of this method is demonstrated for proteins with molecular masses ranging from 5 to 50 kDa, Low molecular mass proteins (<10 kDa) can be efficiently analyzed without any treatment of the bacterial br oth prior to MALDI sample preparation. The MALDI analysis of higher mo lecular weight proteins shows enhanced sensitivity when the bacterial solutions are first sonicated.