A database of 660 peptide ion cross sections: Use of intrinsic size parameters for bona fide predictions of cross sections

An ion trap/ion mobility/time-of-flight mass spectrometry technique has been used to measure collision cross sections for 660 peptide ions generated by tryptic digestion of 34 common proteins. Measured cross sections have been compiled into a database that contains peptide molecular weight and sequence information. The database is used to generate average intrinsic contributions to cross section (size parameters) for different amino acid residues by solving systems of equations that relate the unknown contributions of individual residues to the sequences and cross sections of database peptides. Size parameters are combined with information about amino acid composition to calculate cross sections for database peptides. Bona fide cross section predictions (made prior to measurement) for peptides observed in tryptic digests of sperm whale myoglobin and yeast enolase are made. Eight of 10 predicted cross sections are within 2% of the experimental values and all 10 are within 3.2%. The utility of size parameters for cross section prediction is explored and discussed.