Direct observation of peptide hydrogel self-assembly. Issue 34 (16th August 2022)

• Record Type: Journal Article
• Authors: Adams, Zoë C.; Olson, Erika J.; Lopez-Silva, Tania L.; Lian, Zhengwen; Kim, Audrey Y.; Holcomb, Matthew; Zimmermann, Jörg; Adhikary, Ramkrishna; Dawson, Philip E.
• Is Part Of: Chemical science. Volume 13:Issue 34(2022)
• Page Start: 10020
• Page End: 10028
• Publication Date: 2022-08-16
• Subjects: Chemistry -- Periodicals; 540.5
• DOI: 10.1039/d1sc06562a
• Languages: English
• ISSNs: 2041-6520

Abstract

Abstract : To facilitate the characterization of phase-transitioning molecules, site-specific non-perturbative infrared probes are leveraged for continuous observation of the self-assembly of fibrils in a peptide hydrogel following stopped-flow initiation. Abstract : The characterization of self-assembling molecules presents significant experimental challenges, especially when associated with phase separation or precipitation. Transparent window infrared (IR) spectroscopy leverages site-specific probes that absorb in the "transparent window" region of the biomolecular IR spectrum. Carbon–deuterium (C–D) bonds are especially compelling transparent window probes since they are non-perturbative, can be readily introduced site selectively into peptides and proteins, and their stretch frequencies are sensitive to changes in the local molecular environment. Importantly, IR spectroscopy can be applied to a wide range of molecular samples regardless of solubility or physical state, making it an ideal technique for addressing the solubility challenges presented by self-assembling molecules. Here, we present the first continuous observation of transparent window probes following stopped-flow initiation. To demonstrate utility in a self-assembling system, we selected the MAX1 peptide hydrogel, a biocompatible material that has significant promise for use in drug delivery and medical applications. C–D labeled valine was synthetically introduced into five distinct positions of the twenty-residue MAX1 β-hairpin peptide. Consistent with current structural models, steady-state IR absorption frequencies and linewidths of C–D bonds at all labeled positions indicate that these side chains occupy a hydrophobic region of the hydrogel and that the motion of side chains located in the middle of the hairpin is more restricted than those located on the hairpin ends. Following a rapid change in ionic strength to initiate self-assembly, the peptide absorption spectra were monitored as function of time, allowing determination of site-specific time constants. We find that within the experimental resolution, MAX1 self-assembly occurs as a cooperative process. These studies suggest that stopped-flow transparent window FTIR can be extended to other time-resolved applications, such as protein folding and enzyme kinetics.