Kinetics of gas‐phase hydrogen/deuterium exchange and gas‐phase structure of protonated phenylalanine, proline, tyrosine and tryptophan

Rožman, Marko; Kazazić, Saša; Klasinc̆, L.; Srzić, Dunja

doi:10.1002/rcm.1261

Cited by 14 publications

(22 citation statements)

References 19 publications

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“…Partial deuteration of the amino group is supported by a reduction in the intensity of the NH 2 scissoring band (1600 cm Ϫ1 ). Deuteration at the indole NH site is unlikely, as this site is known to exchange more slowly in [Trp ϩ H] ϩ [34], and given that HDX with CH 3 OD only resulted in a maximum of three deuterium exchanges out of a possible four sites. While a mixture of structures and sites of deuteration is present, it is difficult to establish the relative contribution of each sub-group.…”

Section: Resultsmentioning

confidence: 99%

Observation of zwitterion formation in the gas-phase H/D-exchange with CH₃OD: Solution-phase structures in the gas phase

Polfer

Dunbar

2007

J. Am. Soc. Mass Spectrom.

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Infrared spectroscopy of gas-phase singly deuterated [Trp ϩ K] ϩ (formed by H/D exchange with CH 3 OD) shows that some (ϳ20%) kinetically stable zwitterionic (ZW) conformer is formed, based on the diagnostic antisymmetric CO stretch of the deprotonated carboxylate moiety, as (CO 2 Ϫ ), at 1680 cm Ϫ1 . A majority of the deuterated [Trp ϩ K] ϩ is found to be in the charge solvation (CS) conformation, with deuterium exchange occurring on both the acid and amino groups, which is consistent with H/D scrambling. Interestingly, H/D exchange with the more basic ND 3 reagent did not result in the stabilization of a kinetically stable zwitterion, although it is not clear yet what causes this observation. The result for CH 3 OD shows that H/D exchange can in fact alter the structure of the analyte and, hence, care needs to be taken when interpreting gas-phase H/D exchange studies. Moreover, this result shows the possibility of forming solution-phase structures that are thermodynamically disfavored in the gas phase, thus opening a new area of study. (HDX) is one of the most popular techniques for the structural elucidation of biomolecules in mass spectrometry and has been widely implemented for both solution [1][2][3][4] and gas phase studies [5][6][7][8][9][10][11][12][13][14][15][16][17][18]. In solution, the extent of HDX can be directly related to the solvent accessibility of amino acid residues in proteins. However, in the gas phase there are many structural parameters apart from the surface availability that affect the HDX rates, as illustrated in a recent HDX study on ion-mobilityselected charge states of bovine ubiquitin [17]. Systematic studies on small peptide systems showed that the difference in proton affinity of the biomolecules and deuterated donor reagent plays a crucial role in the HDX mechanism [7][8][9][10]19]. Beauchamp and coworkers [9] suggested that lower basicity reagents, such as D 2 O and CH 3 OD, proceed via a "relay" mechanism [20] for protonated peptides, while the higher basicity ND 3 reagent gives rise to an "onium" mechanism [21]. In the case of amino acids cationized by an alkali metal ion rather than a proton, polar deuterating ligands such as D 2 O can exchange via a similar relay mechanism involving charge solvation-zwitterion (CS-ZW) isomerization [18]. Modeling of observed HDX processes and quantum chemical calculations of the potential surfaces have made a strong circumstantial case that ZW structures are traversed in many cases during HDX with basic partners like D 2 O, CH 3 OD, and ND 3 [14,16,18]. Nevertheless, computations also generally indicate that the bare ZW is sufficiently disfavored energetically that its equilibrium presence in the M ϩ /amino acid would be negligible [22,23].Here, we show unambiguous spectroscopic evidence that bare ZW can in fact be kinetically trapped as a result of the HDX of [Trp ϩ K] ϩ with CH 3 OD. Infrared multiple-photon dissociation (IR-MPD) spectroscopy of metal-tagged amino acids and peptides has already been shown to be a powerful probe for CS ...

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Section: Resultsmentioning

confidence: 99%

Observation of zwitterion formation in the gas-phase H/D-exchange with CH₃OD: Solution-phase structures in the gas phase

Polfer

Dunbar

2007

J. Am. Soc. Mass Spectrom.

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“…25 All experiments were carried out at room temperature of 300 K. H/D exchange experiments were performed according to the procedure mentioned in an earlier publication. 8 Data obtained from mass spectra consist of relative intensities of the mass peaks for D 0 , D 1 , ..., D n (where D n represents an ion species containing a total of n deuterium atoms) measured at a number of time points that correspond to different time delays for the exchange reaction. The kinetic system is treated as n independent exchangeable hydrogen atoms each following a simple pseudo-first-order rate law.…”

Section: Methodsmentioning

confidence: 99%

“…6 The gas-phase H/D exchange studies may give relative exchange rates for different reaction sites, [6][7][8] location of the charge, 7,8 and dependence on the deuterating agent. 6,8 Histidine is one of the 20 naturally occurring R-amino acids. It serves inter alia as a precursor of the hormone histamine, and it regulates the proper utilization of the trace metals and is essential in their rapid excretion, if they were present in excessive amounts.…”

Section: Introductionmentioning

confidence: 99%

Gas-Phase Structure of Protonated Histidine and Histidine Methyl Ester: Combined Experimental Mass Spectrometry and Theoretical ab Initio Study

et al. 2005

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Gas-phase H/D exchange experiments with CD 3 OD and D 2 O and quantum chemical ab initio G3(MP2) calculations were carried out on protonated histidine and protonated histidine methyl ester in order to elucidate their bonding and structure. The H/D exchange experiments show that both ions have three equivalent fast hydrogens and one appreciably slower exchangeable hydrogen assigned to the protonated amino group participating in a strong intramolecular hydrogen bond (IHB) with the nearest N(sp 2 ) nitrogen of the imidazole fragment and to the distal ring NH-group, respectively. It is taken for granted that the proton exchange in the IHB is much faster than the H/D exchange. Unlike in other protonated amino acids (glycine, proline, phenylalanine, tyrosine, and tryptophan) studied earlier, the exchange rate of the carboxyl group in protonated histidine is slower than that of the amino group. The most stable conformers and the enthalpies of neutral and protonated histidine and its methyl ester are calculated at the G3(MP2) level of theory. It is shown that strong intramolecular hydrogen bonding between the amino group and the imidazole ring nitrogen sites is responsible for the stability and specific properties of the protonated histidine. It is found that the proton fluctuates between the amino and imidazole groups in the protonated form across an almost vanishing barrier. Proton affinity (PA) of histidine calculated by the G3(MP2) method is 233.2 and 232.4 kcal mol -1 for protonation at the imidazole ring and at the amino group nitrogens, respectively, which is about 3-5 kcal mol -1 lower than the reported experimental value.

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“…The H/D exchange experiments were performed in a 3 T Fourier transform ion cyclotron resonance (FTICR) mass spectrometer (Extrel FTMS 2001, Madison, WI). The stabilized reagent gas pressure used in the exchange experiments was 2.67-1.33·10 Ϫ5 Pa at an ambient temperature of 300 K. The pressure measurement, H/D exchange experiments and determination of the site-specific reaction rate constants were performed by using the procedure described previously [18]. Repetitive H/D exchange experiments indicate a relative standard deviation of up to 30% for the reported site-specific rate constants.…”

Section: Methodsmentioning

confidence: 99%

“…(2) amino acids Cys and Met with side chains containing sulfur atoms. The absence of gas-phase H/D exchange in reactions of protonated amino acids with D 2 S suggests weak hydrogen bonding within the protonated amino acid-D 2 S complex [18]. Stabilization through formation of a weakly hydrogen bonded reaction complex with D 2 S was not sufficient to overcome the reaction barrier for isotopic exchange.…”

Section: H/d Exchange Of Protonated Aliphatic Amino Acidsmentioning

confidence: 96%

The gas-phase H/D exchange mechanism of protonated amino acids

Rožman

2005

J. Am. Soc. Mass Spectrom.

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A mass spectrometry and Density Functional Theory study of gas-phase H/D exchange in protonated Ala, Cys, Ile, Leu, Met, and Val is reported. Site-specific rate constants were determined and results identify the ␣-amino group as the protonation site. Lack of exchange on the Cys thiol group is explained by the absence of strong intramolecular hydrogen bonding within the reaction complex. In aliphatic amino acids the presence of a methyl group at the ␤-C atom was found to lower the site-specific H/D exchange rate for amino hydrogens. Study of the exchange mechanism showed that isotopic exchange occurs in two independent reactions: in one, only the carboxylic hydrogen is exchanged and in the other, both carboxylic and amino group hydrogens exchange. The proposed reaction mechanisms, calculated structures of various species, and a number of structural findings are consistent with experimental data. (J Am Soc Mass Spectrom 2005, 16, 1846 -1852

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Kinetics of gas‐phase hydrogen/deuterium exchange and gas‐phase structure of protonated phenylalanine, proline, tyrosine and tryptophan

Cited by 14 publications

References 19 publications

Observation of zwitterion formation in the gas-phase H/D-exchange with CH₃OD: Solution-phase structures in the gas phase

Observation of zwitterion formation in the gas-phase H/D-exchange with CH₃OD: Solution-phase structures in the gas phase

Gas-Phase Structure of Protonated Histidine and Histidine Methyl Ester: Combined Experimental Mass Spectrometry and Theoretical ab Initio Study

The gas-phase H/D exchange mechanism of protonated amino acids

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Kinetics of gas‐phase hydrogen/deuterium exchange and gas‐phase structure of protonated phenylalanine, proline, tyrosine and tryptophan

Cited by 14 publications

References 19 publications

Observation of zwitterion formation in the gas-phase H/D-exchange with CH3OD: Solution-phase structures in the gas phase

Observation of zwitterion formation in the gas-phase H/D-exchange with CH3OD: Solution-phase structures in the gas phase

Gas-Phase Structure of Protonated Histidine and Histidine Methyl Ester: Combined Experimental Mass Spectrometry and Theoretical ab Initio Study

The gas-phase H/D exchange mechanism of protonated amino acids

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Observation of zwitterion formation in the gas-phase H/D-exchange with CH₃OD: Solution-phase structures in the gas phase

Observation of zwitterion formation in the gas-phase H/D-exchange with CH₃OD: Solution-phase structures in the gas phase