Kattnig Group

Here you will find a brief summary of our research interests in spin-dependent biophysics.

Fundamentally, biological systems rely on the rules of quantum mechanics as they are ultimately defined at the molecular and sub-molecular scale where quantum phenomena become evident. However, going beyond fundamental presence, quantum biology asks the question: does life crucially rely on quantum phenomena by utilising it to an advantage for physiological function? Recently, studies to address this question have seen rapid growth due to an increase in computational and experimental capability, and the development of advanced theoretical techniques. Yet, there remain many open questions that must be solved. Here, in the Kattnig group we focus on the theoretical description, computational simulation, and experimental assessment of magnetic field effects (MFEs) that are dependent on the property of quantum spin in chemical reactions underlying biological processes and investigating the role that quantum mechanics plays.

Spin-dependent Magnetoreception

Magnetoreception, the ability of some animals to sense the Earth’s weak ~50 micro-tesla magnetic field is one of the grand puzzles of modern science and represents a prominent biological magnetic field effect. One leading hypothesis, centred on the radical pair mechanism (RPM), suggests a compass sense that depends on the magnetic field sensitive quantum spin dynamics of a pair of radicals (a molecule containing at least one unpaired electron) that are formed by a photo-induced electron transfer reaction in the flavoprotein cryptochrome (see Fig. 1). Our magnetoreception research includes: investigating the limit of realistic system complexity, relative orientation of radicals, and inter-radical interactions, understanding the role of the external environment, extending to new models, controlling sensitivity and quantum features, and experimental tests. An overall aim of ours is to elucidate the potentially quantum nature of magnetoreception and more generally understand principles of spin dynamics that can be utilised in future technologies, such as quantum sensors, and medical applications.

Fig. 1: Structure of an avian cryptochrome (PDB identifier: 6PU0, Columba livia), including the central electron transfer chain comprising four tryptophans (W) labelled A (W395), B (W372), C (W318) and D (W369) and ending in the surface exposed tyrosine Y319. Photo-excitation of FAD in cryptochrome initiates consecutive electron transfer reactions of adjacent donors/acceptor pairs (red arrows), producing sequential radical pairs of the form [FAD•− / W•+] and possibly [FAD•− / Y•]. The well separated radical pairs involving WC and WD implicated with magnetoreception. Alternative radical pairs have been discussed.

Open quantum systems

The nontrivial contribution that the external environment often plays in quantum biology necessitates our treatment of systems as so-called open quantum systems (OQS). A prime example of this is radical pair dynamics within the protein cryptochrome. Quantum phenomena such as spin coherence are thought to be washed out through their coupling to any hot, wet and noisy environment, as they are in most quantum technology applications. This would suggest a diminishing of magnetosensitivity in cryptochrome. Surprisingly, studies suggest that the spin relaxation resulting from the protein environment can, under certain conditions, enhance the performance of a cryptochrome-based magnetic compass sensor. In the group we are working on understanding the role of the external environment under the Markovian (memoryless) limit of these studies and beyond to non-Markovian behaviour, which we hypothesise can act as a driver of spin dynamics (see Fig. 2) to counterintuitively enhance the coherence and sensitivity of the system. We employ OQS theory, supported by simulations of protein dynamics, to decipher magnetoreception based on radical-pairs and triads, and more generally understand OQS spin dynamics and optimisation.

Fig. 2: Driven radical motion r(t) of a radical pair of cryptochrome allows the magnetic field sensitivity to be restored, and even enhanced, despite the presence of detrimental inter-radical interactions. We are now investigating if enhancements such as these may be realised by components of the motion of the protein environment.

Three-radical effects

While a model of magnetic field sensitivity based on radical pairs is well established (i.e. the Radical Pair Mechanism), magnetic field effects (MFEs) on radical pairs in low magnetic fields are often strongly attenuated by inter-radical interactions and decoherence processes. Our research suggests that the magneto-sensitivity of radical reactions can be significantly amplified in systems of three and more radicals. In our group we have investigated models of radical triads (see Fig. 3) showing that: remarkable MFEs can be realised due to “bystander radicals” via the dipolar interaction. That principles generalise to n-radical systems for which geometrical symmetry-breaking can further amplify the magnetic field sensitivity. Even more remarkably, the extension of radical pairs by a third reactive “scavenger radical” can overcome the sensitivity suppression arising from inter-radical interactions and render the reaction immune to fast spin relaxation in one of the radicals. This models may credibly facilitate light-independent oxidation reaction schemes for cryptochrome magnetoreception and other biological processes, the existence of which is still discussed controversially due to its necessary involvement of quickly relaxing species. Our ongoing study of these models includes understanding and controlling benefits of driving and protein motion. Beyond magnetoreception we are exploring three-radical MFEs in other biological processes (e.g. lipid-peroxidation and hypomagnetic field effects on neurogenesis), and how they may provide principles for quantum sensing devices.

Fig. 3: (a) Structure of pigeon cryptochrome 4 (PDB: 6PU0). (b) The tryptophan tetrad and relevant radical sites are enlarged and the reaction pathways, including both photoreduction and re-oxidation, are shown by the arrows. Electron-electron dipolar interactions (EED) and radical scavenging can vastly enhance the magnetosensitivity.

Openings

We are always looking for enthusiastic talents to join our group!

PhD Studentships

Fully funded PhD studentships for UK and international applicants are available on a regular basis. Places are competitively filled. Please get in touch if interested to discuss opportunities and project topics.

Postdoc Opportunities

No opportunities are currently available.

Fellowship Applications

We are happy to support applications and host recipients of personal research fellowships (e.g. URF, Marie Curie, 1851, Newton International).