Mass Spectrometry and Ion Mobility Characterization
of Bioactive Peptide–Synthetic Polymer Conjugates
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Abstract
The
bioconjugate BMP2-(PEO-HA)<sub>2</sub>, composed of a dendron
with two monodisperse poly(ethylene oxide) (PEO) branches terminated
by a hydroxyapatite binding peptide (HA), and a focal point substituted
with a bone growth stimulating peptide (BMP2), has been comprehensively
characterized by mass spectrometry (MS) methods, encompassing matrix-assisted
laser desorption ionization (MALDI), electrospray ionization (ESI),
tandem mass spectrometry (MS<sup>2</sup>), and ion mobility mass spectrometry
(IM-MS). MS<sup>2</sup> experiments using different ion activation
techniques validated the sequences of the synthetic, bioactive peptides
HA and BMP2, which contained highly basic amino acid residues either
at the N-terminus (BMP2) or C-terminus (HA). Application of MALDI-MS,
ESI-MS, and IM-MS to the polymer–peptide biomaterial confirmed
its composition. Collision cross-section measurements and molecular
modeling indicated that BMP2-(PEO-HA)<sub>2</sub> exists in several
folded and extended conformations, depending on the degree of protonation.
Protonation of all basic sites of the hybrid material nearly doubles
its conformational space and accessible surface area