MS and MSMS data were analyzed, and peak lists generated using GPS Explorer 3.5 (Applied Biosystems). MS peaks were selected between 800 and 4000 Da and filtered with a signal to noise ratio greater than 15 and to exclude masses derived from trypsin autolysis (842. 51, 1006.48, 1045.56, 2211.1, 2283.18, and 2299.18) . MSMS peaks were selected on the basis of a signal to noise ratio greater than 10 over a mass range of 50 to 20 Da below the precursor mass. A peak density filter was used with no more than 30 peaks per 200 Da and a maximum number of peaks of 65.