Following a Folding Transition with Capillary Electrophoresis and Ion Mobility Spectrometry.
Ion mobility spectrometry (IMS) is increasingly used to describe solution-phase phenomena and has recently been used to establish the presence of multiple intermediates during the folding of a model polypeptide, polyproline. These observations, however, are made on gas-phase structures. Capillary electrophoresis (CE) is a complementary solution-phase technique, also based on the separation of charged species as a function of size and charge. Here, both ion mobility and capillary electrophoresis are used to follow the folding transition of a 13-mer polyproline peptide from the all-cis polyproline I (PPI) conformation to the all-trans polyproline II (PPII) conformation upon immersion in aqueous solvent. Synchronous folding processes are observed using both techniques. Eight conformers are observed using ion mobility. Although only five peaks are observed using capillary electrophoresis, these peaks can be modeled as sums of the observed IMS conformers; this is strong evidence that ion mobility is sampling solution-phase structures. CE measurements provide the first direct evidence that multiple folding intermediates are present in solution.
Department of Chemistry, Moravian College , Bethlehem, Pennsylvania 18018, United States.
John D
JD
Barr
Department of Chemistry, Indiana University , Bloomington, Indiana 47405, United States.
Liuqing
L
Shi
Department of Chemistry, Texas A&M University , College Station, Texas 77843, United States.
David H
DH
Russell
Department of Chemistry, Indiana University , Bloomington, Indiana 47405, United States.
David E
DE
Clemmer
Department of Chemistry, Moravian College , Bethlehem, Pennsylvania 18018, United States.
Alison E
AE
Holliday