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Quantifying the Binding Interactions Between Cu(II) and Peptide Residues in the Presence and Absence of Chromophores
Published on: April 5, 2022
Evidence for the cation-pi interaction between Cu2+ and tryptophan
Hanami Yorita1, Kohei Otomo, Hirotsugu Hiramatsu
1Graduate School of Pharmaceutical Sciences, Tohoku University, Aobayama, Sendai 980-8578, Japan.
Journal of the American Chemical Society
|October 23, 2008
Summary
This study provides the first spectral evidence of cation-pi interactions between copper(II) ions (Cu2+) and tryptophan (Trp). These interactions, observed in a protein motif, are detectable via circular dichroism and UV absorption spectroscopy.
Area of Science:
- Biochemistry
- Spectroscopy
- Protein Structure
Background:
- Cation-pi interactions are crucial noncovalent forces in molecular structures and functions.
- Transition metal cations like Cu2+ are typically excluded from cation-pi interactions due to oxidation and covalency concerns.
Purpose of the Study:
- To provide the first spectral evidence of cation-pi interaction between Cu2+ and tryptophan (Trp).
- To characterize the spectral signatures of this interaction using circular dichroism (CD) and UV absorption.
Main Methods:
- Circular dichroism (CD) spectroscopy to detect spectral changes.
- UV absorption spectroscopy to observe intensity shifts.
- Site-directed mutagenesis and ion substitution to confirm the interaction.
Main Results:
- A distinct negative band at 223 nm in CD spectra was observed for Cu2+-Trp interaction.
- UV absorption showed characteristic intensity changes at 222/231 nm.
- The spectral signals disappeared upon Trp mutation/depletion or Cu2+ replacement with Ni2+.
Conclusions:
- The study presents the first spectral evidence for cation-pi interaction between Cu2+ and Trp.
- The observed CD band at 223 nm can serve as a marker for Cu2+-Trp cation-pi interactions.
- Coordination of negatively charged ligands to Cu2+ may facilitate cation-pi interactions.
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