Gas-phase memory of solution-phase protein conformation: H/D exchange and Fourier transform ion cyclotron resonance mass spectrometry of the N-terminal domain of cardiac troponin C

Electrospray ionization, followed by gas-phase hydrogen/deuterium exchange and Fourier transform ion cyclotron resonance mass analysis provide a means for correlating the gas-phase and solution-phase conformations of a protei n. Multiple gas-phase conformations (based on different rate and extent of deuterium incorporation) are found for each of the 6+, 7+, and 8+ charge st ates of the N-terminal domain of cardiac muscle troponin C (cNTnC). We anal yze the effects of variations in ion accumulation period and capillary temp erature on protein ions of the same charge state following electrospray fro m either aqueous or methanolic solvent. The deuterium exchange-resolved con formations of the 8+ charge state are essentially the same for cNTnC electr osprayed from either solvent. However, the 6+ and 7+ charge states of cNTnC exhibit different gas-phase conformation (reflected in different deuterium uptake profiles) when electrosprayed from aqueous solution and highly orga nic solutions. The present experiments constitute same of the most direct e vidence that gas-phase protein ions can retain some "memory" of their solut ion-phase conformation. (C) 1999 Elsevier Science B.V.