Vapor treatment of electrospray droplets: evidence for the folding of initially denatured proteins on the sub-millisecond time-scale.
The exposure of electrospray droplets generated from either highly acidic or highly basic solutions to basic or acidic vapors, respectively, admitted into the counter-current drying gas, has been shown to lead to significant changes in the observed charge state distributions of proteins. In both cases, distributions of charge states changed from relatively high charge states, indicative of largely denatured proteins, to lower charge state distributions that are more consistent with native protein conformations. Ubiquitin, cytochrome c, myoglobin, and carbonic anhydrase were used as model systems. In some cases, bimodal distributions were observed that are not noted under any solution pH conditions. The extent to which changes in charge state distributions occur depends upon the initial solution pH and the pK(a) or pK(b) of the acidic or basic reagent, respectively. The evolution of charged droplets in the sampling region of the mass spectrometer inlet aperture, where the vapor exposure takes place, occurs within roughly 1 ms. The observed changes in the spectra, therefore, are a function of the magnitude of the pH change as well as the rates at which the proteins can respond to this change. The exposure of electrospray droplets in this fashion may provide means for accessing transient folding states for further characterization by mass spectrometry.
Department of Chemistry, Purdue University, 560 Oval Drive, West Lafayette, IN 47907-2084, USA.
Anastasia
A
Kharlamova
J Corinne
JC
DeMuth
Scott A
SA
McLuckey
D019342:Acetic Acid / Q000737:chemistry; D000818:Animals; D002417:Cattle; D005740:Gases / Q000737:chemistry; D006801:Humans; D006863:Hydrogen-Ion Concentration; D010880:Piperidines / Q000737:chemistry; D011487:Protein Conformation; D011489:Protein Denaturation; D058849:Protein Refolding; D011506:Proteins / Q000737:chemistry* / Q000378:metabolism; D021241:Spectrometry, Mass, Electrospray Ionization / Q000379:methods*; D055672:Static Electricity
D005740:Gases; D010880:Piperidines; D011506:Proteins; C032727:piperidine; D019342:Acetic Acid