Stability of a highly charged noncovalent complex in the gas phase: holomyoglobin

Abstract

Gas phase holomyoglobin (hMb) ions in charge states +7 to +21 were formed by electrospray ionization in combination with a continuous-flow mixing apparatus. Collision cross section measurements show that the highly charged ions are somewhat unfolded in comparison to low charge states but still retain a considerable degree of folding. A new collision model is presented which calculates the relative energies transferred to complexes in tandem mass spectrometry. Tandem mass spectrometry and ion trapping experiments both show that the energies required to dissociate heme from the highly charged heme-protein complexes in the gas phase are similar to those of low charge states, previously shown in literature ion cyclotron resonance experiments to be 0.7-1.0 eV. These energies are comparable to those of the heme binding energy in solution. The results suggest that even for the highly charged hMb ions which have unfolded somewhat, the heme-protein interactions remain relatively unperturbed.

Ion/ion chemistry of high-mass multiply charged ions

“…26 with a random walk simulation of (AG) 8 ions formed initially with average energy at 300 K plus 4 eV in the presence of 1 mtorr helium, which includes dissociation and ion cooling. Figure 26 shows a plot of the fraction of undissociated (AG) 8 ions (diamonds) and the fraction of ion internal energy that remains in the (AG) 8 ions (solid line) as a function of time. At t ϭ 0, k uni is 3700 s Ϫ1 , and k app ϭ 610 s Ϫ1 .…”

“…By 100 s, k uni drops to 1800 s Ϫ1 as a result of energy lost via collisions and, by 500 s, k uni drops to 790 s Ϫ1 . By 1 ms, virtually all ions that will fragment have done so, over 50% of the initial (AG) 8 ion population is left intact. In the absence of a cooling mechanism, only 2-3% of the initial ion population would survive to 1 ms.…”

“…Perhaps the major difference between the energy diagram associated with (MϩnH) nϩ /I Ϫ and those associated with (MϩnH) nϩ /PDCH anions (a combination that yields 100% proton transfer and no adduct formation) is the well-depth FIGURE 26. Composite cooling curve and corresponding fraction of surviving (AG) 8 ions as a function of time, following the input of 4 eV into a 300 K ion. The phenomenologic cooling rate, k app , is 610 s Ϫ1 and the observed dissociation rate, k diss , is 2900 s Ϫ1 .…”

Evidence for the Preservation of Native Inter- and Intra-Molecular Hydrogen Bonds in the Desolvated FK-Binding Protein·FK506 Complex Produced by Electrospray Ionization

“…Excellent calibration fits were also achieved here and have been included in the Supplementary Information of this manuscript (S1). Collision cross sections were used to estimate the amount of internal energy gained by the ions as they traverse the collision cell, according to the model of Douglas et al [34]. Briefly, drag coefficients were calculated based on the diffuse scattering model proposed by Henderson [36].…”

“…The same trend was also observed for the 7+ complexes (see Figure 2c and d, and Table 1). To gain a more quantitative understanding of the degree of destabilization resulting from removal of these interactions, the internal energy (ΔE INT ) transferred to the FKBP·FK506 complex ions was estimated using the method of Douglas et al [34,37]. The results, expressed as a difference between the WT and mutant Ec 50 s, termed ΔΔE INT , are shown in Table 1.…”