title: An experimental study of the solvent-dependent self-assembly/disassembly and conformer preferences of gramicidin A.
abstract: The solvent dependence of self-assembly/disassembly kinetics and conformer preferences of the gramicidin A (GA) dimer is investigated using a combination of techniques, viz., electrospray ionization-ion mobility-mass spectrometry (IM-MS), collision-induced dissociation (CID), and hydrogen/deuterium exchange (HDX)-MS. IM-MS measurements reveal that there are possibly three distinct GA dimeric species, detected as sodium ion adduct ions [2GA + 2Na](2+), and these are assigned as the parallel β-helix, antiparallel β-helix, and head-to-head dimer. The monomerization kinetics and equilibrium abundances of the dimer ions depend upon solvent polarity. The antiparallel β-helix was the thermodynamically preferred species in less polar solvents. HDX measurements and collision-induced dissociation (CID) of the intermediate complex confirm the well-protected dimer geometry with strong intermolecular hydrogen bonds. This combined IM-HDX-CID methodology provides a comprehensive view of GA self-assembly/disassembly in low dielectric solutions, showing its potential utility in solving solution-phase protein self-assembly/disassembly kinetics and providing structural information of the multimers at the same time.
authors.affiliation: Laboratory for Biological Mass Spectrometry, Department of Chemistry, Texas A&M University, College Station, Texas 77843, United States.
authors.forename: Liuxi
authors.initials: L
authors.lastname: Chen
authors.forename: Shu-Hua
authors.initials: SH
authors.lastname: Chen
authors.forename: David H
authors.initials: DH
authors.lastname: Russell
mesh_terms: D000595:Amino Acid Sequence; D006096:Gramicidin / Q000737:chemistry*; D008969:Molecular Sequence Data; D011487:Protein Conformation; D012997:Solvents / Q000737:chemistry*; D021241:Spectrometry, Mass, Electrospray Ionization / Q000379:methods*
chemical_list: D012997:Solvents; D006096:Gramicidin