DEUTERIUM-EXCHANGE OF ALPHA-HELICES AND BETA-SHEETS AS MONITORED BY ELECTROSPRAY-IONIZATION MASS-SPECTROMETRY

Deuterium exchange was monitored by electrospray ionization mass spect rometry (ESI-MS) to study the slowly exchanging (hydrogen bonded) pept ide hydrogens of several alpha-helical peptides and beta-sheet protein s. Polypeptides were synthetically engineered to have mainly disordere d, alpha-helical, or beta-sheet structure. For 3 isomeric 31-residue a lpha-helical peptides, the number of slowly exchanging hydrogens as me asured by ESI-MS in 50% CF3CD2OD (pD 9.5) provided estimates of their alpha-helicities (26%, 40%, 94%) that agreed well with the values (17% , 34%, 98%) measured by circular dichroic spectroscopy in the same non deuterated solvent. For 3 betabellins containing a pair of beta-sheets and a related disordered peptide, their order of structural stability (12D > 12S > 14D > 14S) shown by their deuterium exchange rates in 10 % CD3OD/0.5% CD3CO2D (pD 3.8) as measured by ESI-MS was the same as th eir order of structural stability to unfolding with increasing tempera ture or guanidinium chloride concentration as measured by circular dic hroic spectroscopy in water. Compared to monitoring deuterium exchange by proton NMR spectrometry, monitoring deuterium exchange by ESI-MS r equires much less sample (1-50 mu g), much shorter analysis time (10-9 0 min), and no chemical quenching of the exchange reaction.