EPR of Cu²⁺ Prion Protein Constructs at 2 GHz Using the g_⊥ Region to Characterize Nitrogen Ligation

Authors

James S. Hyde, Medical College of Wisconsin
Brian Bennett, Marquette UniversityFollow
Eric D. Walter, University of California - Santa Cruz
Glenn L. Millhauser, University of California - Santa Cruz
Jason Walter Sidabras, Medical College of Wisconsin
William E. Antholine, Medical College of Wisconsin

Document Type

Article

Language

eng

Format of Original

9 p.

Publication Date

4-2009

Publisher

Elsevier

Source Publication

Biophysical Journal

Source ISSN

0006-3495

Original Item ID

doi: 10.1016/j.bpj.2009.01.034

Abstract

A double octarepeat prion protein construct, which has two histidines, mixed with copper sulfate in a 3:2 molar ratio provides at most three imidazole ligands to each copper ion to form a square-planar Cu²⁺ complex. This work is concerned with identification of the fourth ligand. A new (to our knowledge) electron paramagnetic resonance method based on analysis of the intense features of the electron paramagnetic resonance spectrum in the g_⊥ region at 2 GHz is introduced to distinguish between three and four nitrogen ligands. The methodology was established by studies of a model system consisting of histidine imidazole ligation to Cu²⁺. In this spectral region at 2 GHz (S-band), g-strain and broadening from the possible rhombic character of the Zeeman interaction are small. The most intense line is identified with the M_I = +1/2 extra absorption peak. Spectral simulation demonstrated that this peak is insensitive to cupric A_x and A_y hyperfine interaction. The spectral region to the high-field side of this peak is uncluttered and suitable for analysis of nitrogen superhyperfine couplings to determine the number of nitrogens. The spectral region to the low-field side of the intense extra absorption peak in the g_⊥ part of the spectrum is sensitive to the rhombic distortion parameters A_x and A_y. Application of the method to the prion protein system indicates that two species are present and that the dominant species contains four nitrogen ligands. A new loop-gap microwave resonator is described that contains ∼1 mL of frozen sample.

Comments

Published Version. Biophysical Journal, Vol. 96, No. 8 (April 2009): 3354-3362. DOI. © 2009 Elsevier (Cell Press). Used with permission.

Brian Bennett was affiliated with Medical College of Wisconsin at the time of publication.

Recommended Citation

Hyde, James S.; Bennett, Brian; Walter, Eric D.; Millhauser, Glenn L.; Sidabras, Jason Walter; and Antholine, William E., "EPR of Cu²⁺ Prion Protein Constructs at 2 GHz Using the g_⊥ Region to Characterize Nitrogen Ligation" (2009). Physics Faculty Research and Publications. 67.
https://epublications.marquette.edu/physics_fac/67