Conformational changes in β‐endorphin as studied by electrospray ionization mass spectrometry

Abstract

Because of a wide range of physiological functions, the structure of beta-endorphin (BE) is of great interest. In this study, conformational changes in BE induced by methanol are explored with electrospray ionization-mass spectrometry (ESI-MS). Differences in the charge-state distribution (CSD) and the extent of hydrogen/deuterium (H/D) exchange were used to monitor the conformational changes. The latter experiments were conducted via time-resolved ESI-MS in a continuous-flow apparatus. Both these techniques demonstrate that BE exists in a random coil open structure in aqueous media, but it acquires a more compact conformation with increased concentration of methanol. The H/D exchange experiments reveal that BE forms 61% alpha-helix in mixed solvents.

The study of protein conformation in solution via direct sampling by desorption electrospray ionization mass spectrometry

“…Another example in this regard is the study of the methanol induced conformational change of a polypeptide β-endorphin, an endogenous opioid that acts as a neuropeptide in the central nervous system [39], by DESI. β-Endorphin has six basic sites consisting of five lysine residues and one N-terminal amino group.…”

“…Table 1 gives the relative abundance of all ions measured under different amounts of methanol in solution. It is known that the alcohol such as methanol can induce helicity of β-endorphin, which will further reduce the number of accessible basic sites in peptides [39]. In other words, β-endorphin has a more compact structure in methanol/ water than in water.…”

Trifluoroethanol-induced conformational changes in α- and β-neoendorphins monitored using hydrogen/deuterium exchange mass spectrometry and circular dichroism spectroscopy

“…The time-resolved HX experiments further support the existence of secondary structures for neoendorphins in the presence of TFE. In water, all of the labile hydrogens were exchanged within 30 s. This type of fast HX behavior is a common phenomenon for several other peptides [28][29][30][31][32][33][34][35]. The HX rates were relatively slower in 50% and 80% solvent systems.…”

“…This methodology has been successfully used to probe the higher-order structures of proteins and peptides [24][25][26][27]. We have also applied these methodologies (HX-ESI-MS and HX-ESI-MS/MS) to investigate solvent-induced conformational changes in adrenocorticotropic hormone (ACTH), ␤-endorphin, methionine and leucine enkephalins, dynorphin (1-13) and lipid vesicles-bound angiotensins [28][29][30][31][32].…”

Protein Folding and Protein-Ligand Interactions Monitored by Electrospray Mass Spectrometry

“…Proteins adopting tightly folded structures generally show relatively low charge states, whereas unfolding in solution greatly enhances the degree of protonation during ESI [73,74]. Based on this empirical relationship, ESI-MS has become a widely used method for probing protein conformational changes in solution [43,[75][76][77][78][79][80][81]. Interestingly, ESI-MS experiments carried out in positive ion mode appear to be more sensitive to protein structural changes than in negative ion mode [82].…”