Effects of chromatography conditions on intact protein separations for top-down proteomics.

For top-down proteomics, nano-reversed phase liquid chromatography (RPLC) plays a major role in both single and multidimensional protein separations in an effort to increase the overall peak capacity for the resolution of complex protein mixtures prior to mass spectrometry analysis. Effects of various chromatography conditions, including alkyl chain length in the stationary phase, capillary column temperature, and ion-pairing agent, on the resolution of intact proteins are studied using nano-RPLC-electrospray ionization-mass spectrometry. Optimal chromatography conditions include the use of C18 column heated at 60 degrees C and the addition of trifluoroacetic acid instead of heptafluorobutyric acid as the ion-paring agent in the mobile phase. Under optimized chromatography conditions, there are no significant differences in the separation performance of yeast cell lysates present in the native versus denatured states. Denatured yeast proteins resolved and eluted from nano-RPLC can be subjected to proteolytic digestion in an on- or off-line approach to provide improved protein sequence coverage toward protein identification in a combined top-down/bottom-up proteome platform.