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Physics of biology and medicine
Reference:

Magnetic sensor based on DNA

Hore Peter

ORCID: 0000-0002-8863-570X

PhD, Fellows of the Royal Society, Professor, University of Oxford

., Great Britain, Oxford, South Parks Road, .

peter.hore@chem.ox.ac.uk

DOI:

10.7256/2730-0560.2023.1.40610

EDN:

SWLCAN

Review date:

28-04-2023


Publish date:

08-06-2023


Abstract: The following article, offered to the reader in Russian translation, was written by a famous English scientist, Professor Peter Hore coordinates research abroad in the field of spin-chemical mechanisms, which are believed to underlie the ability of some animal species to navigate in the Earths magnetic field and use the geomagnetic landscape in seasonal migrations. P. Hore, a Fellow of the Royal Society, is a British chemist. He is a Professor of Chemistry at the University of Oxford and fellow of Corpus Christi College, Oxford. P. Hore is the author of many research articles and textbooks, primarily in the area of NMR, EPR, spin chemistry, and magnetoreception during bird migration. Original article in English is an open access article published under an ACS AuthorChoice License, which permits copying and redistribution of the article or any adaptations for non-commercial purposes. This translation is an unofficial adaptation of an article that appeared in an ACS publication. ACS has not endorsed the content of this adaptation or the context of its use. The translation into Russian has been made by V. Binhi in accordance with the terms of the License and is as literal as possible.


Keywords:

magnetobiology, photolyase, DNA repair, magnetic compass, cryptochrome, spin chemistry, retina, magnetoreception, quantum biology, radical pair mechanism

This article is automatically translated. You can find original text of the article here.

This is an open access article published under the ACS AuthorChoice License, which authorizes the copying and distribution of the article or any of its adaptations for non-commercial purposes.

Published on March 13, 2018

DOI: 10.1021/acscentsci.8b00091
ACS Cent. Sci. 2018, 4, 318?320

How to quote this article:

ACS Cent. Sci.2018, 4, 3, 318320
Publication Date: March 13, 2018
https://doi.org/10.1021/acscentsci.8b00091
Copyright 2018 American Chemical Society


The sensitivity of DNA repair enzymes to weak magnetic fields may be related to the mechanism by which birds sense the Earth's magnetic field.

Northern kamenka are small migratory songbirds, whose weight is approximately equal to the weight of an AA battery, annually fly 30,000 km from Alaska through Asia to Kenya and back [1]. Their ability to do this depends crucially on the presence of an internal magnetic compass, with which you can sense the Earth's magnetic field. It seems that all migratory birds have such a light-dependent compass. Although it is clear that the primary magnetoreceptors are located in the retina of birds, the chemical identity of the sensors and the biophysical sensory mechanism remain a mystery [2]. Recently, Jacqueline Barton and her colleagues from the California Institute of Technology, in collaboration with Dongping Zhong from Ohio State University, intriguingly suggested that a DNA repair enzyme may be responsible for this [3].

The enzyme in question is photolyase, a photoactive protein containing flavinadenine dinucleotide (FAD) as the main chromophore. Photoliases repair DNA damage, for example, by cleavage of cyclobutane-pyrimidine (CPD) dimers, which can be formed by neighboring thymine bases after absorption of ultraviolet light (Fig. 1). The repair mechanism includes photoexcitation by FADH-blue light, which is a fully restored state of the cofactor, followed by electron transfer from flavin to damaged DNA with the formation of a pair of radicals, with one unpaired electron on CPD and another on flavin (FADH*). Then the cyclobutane bonds binding the two thymines are sequentially broken, and the electron returns to the flavin. The whole process is completed within a nanosecond [4].

Fig. 1. The mechanism of photoliase DNA repair mediated by FAD. Reprinted with permission, see [11]. Copyright owned by Macmillan Publishers Limited, 2015

Hyperlink to Fig. 1:

https://www.nature.com/articles/ncomms8302/figures/1

A new study by Zwang et al. [3] uses a fine electrochemical method to monitor CPD damage repair in monolayers of DNA duplexes of 29 base pairs associated with Escherichia coli photolyase. It is noteworthy that the rate of repair, or restoration, depends on the intensity and direction of the external magnetic field created by a neighboring Nd-Fe-B alloy magnet. Even weaker magnetic fields than those on Earth (about 40 T in the Barton laboratory) have a noticeable effect on the recovery efficiency.

Individual molecules are so weakly magnetic that their interaction with a magnetic field of 40 T is usually completely suppressed by their chaotic thermal movements, the energy of which is a million times greater. However, radical pairs have unique properties: they can exist in long-lived coherent spin states and enter into spin-selective chemical reactions. These features make them sensitive to the smallest magnetic interactions [2]. Indeed, the currently popular hypothesis of the mechanism of compass magnetoreception is based on light-induced radical pairs in a closely related protein, cryptochrome [5]. Cryptochromes are widely found in nature, including in the retina of birds [6], have a set of functions and are usually considered the evolutionary descendants of photolyases. They also contain the FAD chromophore, but form magnetically sensitive radical pairs in another light-dependent way: by electron transfer from aromatic amino acid residues to fully oxidized FAD [7]. For the most part, cryptochromes do not have the function of DNA repair.

Barton's study is the first to report the effect of a magnetic field on photoliasemediated DNA repair, and the results seem to be consistent with the magnetochemical mechanism of radical pairs. The magnetic field inhibits DNA repair, as one would expect from a radical pair created in a singlet state, and the effect reaches saturation at a plausible field strength (?3 MT). Also, as expected, the change in the repair rate does not depend on the magnetic field inversion, but is otherwise sensitive to the angle between the field vector and the alignment axis of protein-DNA complexes. What is important for a potential compass sensor, the Barton magnetic effect is significantly greater than anything previously reported for cryptochromes, where effects were observed only for magnetic fields of more than 1 MT [7].

However, there are some mysterious aspects. Considering the lifetime and the separation of radicals in photolyase, it is surprising that the effect of the magnetic field can be observed at all. All radicals disappear within 1 ns, and in particular the radical pair, which is most likely magnetically sensitive. This is a pair containing the FAD radical and the CPD molecule, in which the C5-C5' bond is broken, but not the C6-C6' bond. According to ultrafast spectroscopic measurements, it lives less than 100 ps [8]. But in order to react significantly to the magnetic field of 40 T, a radical pair must exist at least 1 microsecond [9].

Moreover, the two radicals are located quite close to each other: the edge of the isoalloxazine ring FAD is removed by 0.8 nm from the 5' side of CPD and only 0.43 nm from the 3' side [8]. At these distances, one can expect a strong electron exchange interaction that would lock the radical pair in its original singlet spin state and block any effect of much weaker interactions that cause dependence on the magnetic field. This problem becomes even more serious if, as assumed [3], the radical pair is limited by the pyrimidine dimer. For example, biradical 1,4, formed as a result of homolytic breakage of the C5-C5' bond (fig. 5 in Zwang et al. [3]), will have an even greater exchange interaction than the more traditional pair FADH* + CPD*-.

One of the ways to resolve some of these uncertainties may be to use D. Zhong's femtosecond methods [3] to search for the influence of the magnetic field on both the lifetime of ~100-ps of the FADH*+[TT]*- state and the branching coefficient of its straight line (-> FADH*+T+T*-) and reverse (-> FADH-+[TT])reaction stages. In addition, if this is not already known, it might be worth establishing the presence and distribution of photolyases in the retina of migratory songbirds.



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