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Title: Secondary Structures of Ubiquitin Ions Soft-Landed onto Self-Assembled Monolayer Surfaces

The secondary structures of multiply charged ubiquitin ions soft-landed onto self-assembled monolayer (SAM) surfaces were studied using in situ infrared reflection-absorption spectroscopy (IRRAS). Two charge states of ubiquitin, 5+ and 13+, were mass selected separately from a mixture of different charge states produced by electrospray ionization (ESI). The low 5+ charge state represents a native-like folded state of ubiquitin, while the high 13+ charge state assumes an extended, almost linear conformation. Each of the two charge states was soft-landed onto a CH3- and COOH-terminated SAM of alkylthiols on gold (HSAM and COOH-SAM). HSAM is a hydrophobic surface known to stabilize helical conformations of soft-landed protonated peptides, whereas COOH-SAM is a hydrophilic surface that preferentially stabilizes β-sheet conformations. IRRAS spectra of the soft-landed ubiquitin ions were acquired as a function of time during and after ion soft-landing. Similar to smaller peptide ions, helical conformations of ubiquitin are found to be more abundant on HSAM, while the relative abundance of β-sheet conformations increases on COOH-SAM. The initial charge state of ubiquitin also has a pronounced effect on its conformation on the surface. Specifically, on both surfaces, a higher relative abundance of helical conformations and lower relative abundance of β-sheet conformations is observedmore » for the 13+ charge state compared to the 5+ charge state. Time-resolved experiments indicate that the α-helical band in the spectrum of the 13+ charge state slowly increases with time on the HSAM surface and decreases in the spectrum of the 13+ charge state on COOH-SAM. These results further support the preference of the hydrophobic HSAM surface toward helical conformations and demonstrate that soft-landed protein ions may undergo slow conformational changes during and after deposition.« less
Publication Date:
OSTI Identifier:
Report Number(s):
Journal ID: ISSN 1520-6106; KC0302020
DOE Contract Number:
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Physical Chemistry. B, Condensed Matter, Materials, Surfaces, Interfaces and Biophysical Chemistry; Journal Volume: 120; Journal Issue: 22
American Chemical Society
Research Org:
Pacific Northwest National Laboratory (PNNL), Richland, WA (US)
Sponsoring Org:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
Country of Publication:
United States
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY Soft-landing; Protein folding; Secondary structure; Conformation; Ubiquitin; Electrospray ionization (ESI); Grazing angle infrared reflection-absorption spectroscopy (IRRAS); Self-assembled monolayers (SAMs)