Magnetoreception of Photoactivated Cryptochrome 1 in Electrochemistry and Electron Transfer

Abstract

Cryptochromes are flavoproteins whose photochemistry is important for crucial functions associated with phototropism and circadian clocks. In this report, we, for the first time, observed a magnetic response of the cryptochrome 1 (CRY1) immobilized at a gold electrode with illumination of blue light. These results present the magnetic field-enhanced photoinduced electron transfer of CRY1 to the electrode by voltammetry, exhibiting magnetic responsive rate constant and electrical current changes. A mechanism of the electron transfer, which involves photoinduced radicals in the CRY, is sensitive to the weak magnetic field; and the long-lived free radical FAD^•- is responsible for the detected electrochemical Faradaic current. As a photoreceptor, the finding of a 5.7% rate constant change in electron transfer corresponding to a 50 μT magnetic field may be meaningful in regulation of magnetic field signaling and circadian clock function under an electromagnetic field.

Figure 1

Illustration of the protocol for the SAM formation and CRY1s immobilization on the gold slide electrode and a schematic of the home-setup, optomagnetic electrochemical system used for the electrochemical study of the immobilized CRY1s with a blue light illumination.

Figure 2

(A) Cyclic voltammograms for the gold slide surface immobilized with CRY1 with and without blue light excitation in the absence of the magnetic field and with blue light excitation under different magnetic fields at the scan rate of 4 V s^–1. (B) Time profiles for the surface concentration of immobilized CRY1 with blue light excitation at the scan rate of 4 V s^–1 in the absence of the magnetic field.

Figure 3

(A) Linear dependence of the peak current on the voltage scan rate under different magnetic fields. (B) Dependence of the peak potential on log(scan rate, ν) under different magnetic fields and fits of the data to the extended Marcus model for electron transfer (at λ = 0.8 eV). Note that the scan rates (ν) are 0.2, 0.5, 1, 2, 4, 6, and 8 V s^–1.

Figure 4

Proposed electrochemical reaction and electron transfer pathways of CRY1 immobilized at the gold electrode based on the photocycle scheme of CRYs and the magnetic sensitive radical pair mechanism.

Figure 5

Magnetic sensitivity of (A) peak current (at 4 V s^–1 scan rate) vs field strength and (B) plot of ln(k_m/k₀) vs field strength for the gold slide surface immobilized with CRY1 under blue light excitation with a linear fit. Note that k_m and k₀ are the calculated rate constant k⁰ values in the presence and absence of magnetic fields, respectively.