Conformational studies of bioactive peptides by mass spectrometry

This dissertation research aims to develop and apply mass spectrometry (MS)-based methods to investigate the conformational states of bioactive peptides. Two protocols, charge-state distribution (CSD) and hydrogen/deuterium exchange (HDX), were employed to monitor the conformational changes of the peptides induced by trifluoroethanol (TFE)---a membrane-mimetic solvent. This dissertation consists of three distinct projects: (i) structural characterization of methionine enkephalin and leucine enkephalin by H/D exchange and electrospray ionization tandem mass spectrometry (ESI/MS/MS) (Chapter 3); (ii) conformational characterization of dynorphin A (1--13) by CSD and HDX-MS (Chapter 4); and (iii) conformational studies of human corticotropin-releasing factor (hCRF) by ESI- and matrix-assisted laser desorption/ionization (MALDI)-MS (Chapter 5). Chapters 1 and 2 describe the general background about proteins/peptides and mass spectrometry techniques used in this research.; Conformational changes in two endogenous opioid active pentapeptides methionine enkephalin (Met-enk) and leucine enkephalin (Leu-enk) induced by TFE were identified using hydrogen/deuterium exchange, coupled with electrospray ionization mass spectrometry. The exchange features in individual amino acid residues were characterized by acquiring tandem mass spectra of the deuterated peptides. The exact identity of the labile hydrogens involved in HDX reveals that the monomeric form of both peptides adopts an unfolded conformation in aqueous solvent, but prefers the 5→2 beta-turn secondary structure under the membrane-mimetic environment. The ESI mass spectra of Met-enk and Leu-enk also reveal that the dimer structure of these peptides coexists with the monomer. The extent of the dimer structure is dependent upon the peptide concentration and nature of the solvent. Non-polar solvents facilitate dimer formation.; Dynorphin A (1--13) is a kappa-selective opioid peptide, with the first five N-terminal residues identical to that of leucine enkephalin. Charge-state distribution, time-resolved H/D exchange, and H/D exchange coupled with tandem mass spectrometry were applied to elucidate the structure of dynorphin A (1--13). It has no orderly structure in aqueous solvent, but in TFE, the N-terminal segment from residues 1--9 adopts a folded structure and the remaining four residues at the C-terminus are in a random conformation.; The conformational changes of human corticotropin-releasing factor induced by TFE are characterized using charge-state distribution and H/D exchange measurements coupled with ESI and MALDI mass spectrometry techniques. Back-exchange with ESI and forward-exchange with MALDI were employed respectively to monitor the conformational changes. The results show that CRF is predominantly a random coil flexible structure in aqueous solvent, but assumes a helical structure in TFE/water medium. The degree of helicity is estimated to be 65% in 50% TFE.