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An Experimental Study of the Solvent-Dependent Self-Assembly/Disassembly and Conformer Preferences of Gramicidin A
journal contribution
posted on 2013-08-20, 00:00 authored by Liuxi Chen, Shu-Hua Chen, David H. RussellThe 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.