A mechanistic study of the H/D exchange reactions of protonated arginine and arginine-containing Di- and tripeptides

Abstract

The gas-phase H/D exchange reactions of arginine (R) and arginine-containing di-and tri-peptide (gly-arg (GR), arg-gly (RG), gly-gly-arg (GGR), gly-arg-gly (GRG) and arg-gly-gly (RGG)) [M ϩ H] ϩ ions with deuterated ammonia (ND 3 ) were investigated by using Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR), ion mobility-mass spectrometry (IM-MS), ab initio and density functional theory-based molecular orbital calculations and molecular modeling. Three exchanges are observed for arginine and argininecontaining tri-peptide [M ϩ H] [15]. Valentine and Clemmer used ion mobility-mass spectrometry to examine the conformation dependence of H/D exchange reactions, and suggested that ion conformation has a significant effect on H/D exchange [16,17].Compared with the intensive investigations carried out on the conformational characterization of peptides and proteins using solution-phase H/D exchange reaction chemistry, the corresponding gas-phase studies are much less comprehensive. The key question regarding gas-phase H/D exchange is: does the "solvent molecule," i.e., H/D exchange reagent, sample the entire "available surface area" of the peptide/protein ion, or is H/D exchange limited by other factors? For example, are all solution phase labile hydrogen atoms exchangeable in the gas phase and are the reactivities of all exchangeable hydrogen atoms similar? Dookeran and Harrison studied the H/D exchange reactions of 18 naturally occurring amino acids and selected di-and tripeptides with ND 3 , and reported that amino acid [M ϩ H] ϩ ions containing hydroxyl, carboxyl, and amine side chains exchange all labile hydrogen atoms, whereas the side-chain hydrogen atoms of glutamine, asparagine, and histidine [M ϩ H] ϩ ions exchange less readily, and tyrosine and arginine [M ϩ H] ϩ ions do not undergo significant exchange [18]. In a separate study, Lebrilla et al. found that the carboxylic acid group of glycine and aliphatic amino acid [M ϩ H] ϩ ions (alanine, valine, leucine, isoleucine, and proline) undergo H/D exchange three to 10 times faster than the NAddress reprint requests to Dr.

Gas Phase Hydrogen/Deuterium Exchange of Arginine and Arginine Dipeptides Complexed with Alkali Metals

“…Sample mass spectra for exchange of Gly-Arg-K + as a function of time with D 2 O, demonstrating the typical isotopic resolution obtained in the quadrupole ion trap for exchange of these peptides complexed with metals are included in the Supporting Information. Figure shows the H/D exchange of protonated Arg-Gly and Gly-Arg, which partially exchange 1 of 9 labile hydrogens with D 2 O in 20 s. This is similar to the extent of exchange observed for these compounds with ND 3 . This slow exchange has been attributed to the high proton affinity of arginine, ,, although more extensive exchange has been observed for larger protonated arginine-containing peptides, and is attributed to SB formation. ,, …”

“…Figure shows the H/D exchange of protonated Arg-Gly and Gly-Arg, which partially exchange 1 of 9 labile hydrogens with D 2 O in 20 s. This is similar to the extent of exchange observed for these compounds with ND 3 . This slow exchange has been attributed to the high proton affinity of arginine, ,, although more extensive exchange has been observed for larger protonated arginine-containing peptides, and is attributed to SB formation. ,, …”

“…20 Exchange with ND 3 in a Fourier transform ion cyclotron resonance spectrometer of protonated arginine and small arginine peptides combined with ab initio calculations shows slow exchange (between one and three exchanges in 1 s) through a proposed "solvated salt bridge" intermediate. 15 Similar slow exchange results for protonated dipeptides Arg-Gly and Gly-Arg with ND 3 were observed in a collision cell of a tandem mass spectrometer. 21 The rapid H/D exchange of bradykinin and its derivatives with D 2 O has been used to infer the presence of a zwitterion.…”

“…Figure 2 shows the H/D exchange of protonated Arg-Gly and Gly-Arg, which partially exchange 1 of 9 labile hydrogens with D 2 O in 20 s. This is similar to the extent of exchange observed for these compounds The Journal of Physical Chemistry A ARTICLE with ND 3 . 15 This slow exchange has been attributed to the high proton affinity of arginine, 15,21,44 although more extensive exchange has been observed for larger protonated argininecontaining peptides, and is attributed to SB formation. 4,6,9 The rate of H/D exchange of both Gly-Arg and Arg-Gly increased significantly when complexed with alkali metals compared to the protonated form, as shown in Figure 3 for Gly-Arg and Figure 4 for Arg-Gly.…”

Probing the mechanisms and dynamics of gas phase hydrogen–deuterium exchange reactions of sodiated polyglycines

“…Even though it is intuitively appealing to consider that, in analogy with condensed phase experiments, the more compact the structure, the fewer the accessible exchangeable hydrogens and therefore the smaller the number of exchanges to be observed, there are several recent reports which provide counter examples. [8][9][10][11][12] It can be argued that the electrostatic stabilization which arises from the association of the charged analyte and the H-D exchange reagent may be enough to trigger conformational changes in the analyte, precluding any direct relationship between the rate and number of H-D exchanges and a specific structure. [13][14][15] It remains, however, that reactions occurring at different rates within a family of related species may be interpreted as showing that starting structures are different.…”