CHARACTERIZATION OF THE CONFORMATIONS OF ANTIGENIC PEPTIDES OF PROTEIN LACTATE-DEHYDROGENASE (LDH-C4) BY ELECTROSPRAY-IONIZATION MASS-SPECTROMETRY

The conformations of several rationally designed antigenic peptides th at mimic, to varying degrees, an antibody-binding region of protein la ctate dehydrogenase isozyme (LDH-C4) are investigated by deuterium/hyd rogen exchange and electrospray ionization mass spectrometry (ESI-MS), The approach involves monitoring the reverse-exchange of deuterium, i ncorporated at the labile sites in the peptides, with hydrogen as a fu nction of time by ESI-MS. Idealized forms of a segment of the native a ntigen are shown to be more conformationally restricted than the nativ e peptide based on level of deuterium that remains incorporated at the labile sites over time. From the number of amide groups of the peptid e backbone that retain deuterium, estimates of the helical content of each peptide have been measured that are in close agreement with those determined by Fourier transform infrared (FTIR) spectroscopy in separ ate experiments, A single amino acid substitution in the idealized hel ical construct results in a conformational change easily detected by t he deuterium exchange ESI-MS method, The approach is shown to be a via ble method for characterizing the conformations of protein antigens at the local level and for screening the conformations of antigenic pept ides designed to elicit optimal immune responses. (C) 1997 John Wiley & Sons, Ltd.