European Spallation Source
Life Science at the European Spallation Source
The European Spallation Source (ESS) is a project to build a multi-disciplinary research laboratory based on the world’s most powerful neutron source. That facility will enable researchers to use neutrons to study a broad range of materials, from polymers and pharmaceuticals, to membranes and molecules. The source will be as much as 100 times brighter than existing facilities, opening up new possibilities for researchers studying all kinds of soft matter, particular biological structures and life science research.
Life science research faces numerous challenges in the study of biological processes that occur on the atomic to cellular scale, such as large macromolecular complexes, the function of water in enzyme mechanisms and drug/substrate/product binding, and the role of biological macromolecules in membranes. These processes present themselves in diverse applications, from biofuels to cancer research.
Neutrons are ideal probes to study biological samples. They are very sensitive to hydrogen rich materials, and even better reporters on hydrogen’s isotope, deuterium. In the past, exploiting the full value neutrons for life science has for several reasons. There are very instruments designed specifically for the use of life science experiments. Existing neutron sources produce very few neutrons, which means performing an experiment requires very large samples and a lot of time. In addition, most existing facilities don’t have the kind of laboratories necessary to prepare the samples.
The European Spallation Source will change all that. With a combination of unparalleled neutron production, and sophisticated support facilities, ESS will open up the field of life sciences to neutrons and make an entirely new set of science and experiments possible.
Atomic Resolution Macromolecular Structures
The historical workhorse for working with atomic resolution determination of protein and DNA/RNA structures is X-ray crystallography. Unfortunately, X-ray crystallography cannot easily be used to see hydrogen atom positions in biomolecules. Those atoms make up ~50% of all atoms in proteins and are functionally involved with a variety of processes such as hydrogen-bonding, protein folding, enzyme catalysis, and hydration.
Neutrons are complementary to X-ray crystallography and help us see deuterium atom positions, for example, in a human enzyme such as carbonic anhydrase. This kind of information can be used to understand and improve enzyme kinetics or to design better drugs with clinical applications. Since ESS will produce more neutrons than we can get a today’s sources, Neutron Macromolecular Crystallography is expected to be very interesting developing field. With dedicated instruments in this field, it will become possible to apply this method to a much wider range of biological problems or to study things that are currently intractable due to sample size limitations.
Solution Structure Of Large Macromolecular Complexes
Large, complex biological systems cannot be studied with crystallography due to their size and inherent flexibility. These kinds of samples are very well suited to another technique called small angle neutron scattering (SANS). Using an approach called contrast matching, researcher can mask parts of large groups of molecules and highlight areas of interest. In this way one can extract a lot of information about the size, structure, and binding behavior of molecules in a complex while being able to change the environment through pH, ionic strength, or even substituting different binding partners.
The SANS technique is highly complementary to electron microscopy and small angle X-ray scattering methods, but it has one big advantage. Neutrons enable isotope labeling, something not distinguishable with X-ray techniques alone. The high brightness of the ESS will increase the range of problems that can be studied.
Dynamic Measurements Of Biomolecules
Proteins are by their nature not perfectly rigid, static molecules and many times studying the dynamics of these molecules is important to understand their proper function. These dynamics can occur over many time and length scales, making them difficult to study.
To study these complicated motions scientists combine a variety of techniques, such as nuclear magnetic resonance (NMR) and optical spectroscopy, neutron and X-ray scattering. Two methods that are well suited to these kinds of studies are inelastic and quasi-elastic neutron scattering methods (IQNS and QENS, respectively). They cover length scales from the Ångstrom to nanometer scale, and from the pico- to milli-second time range.
It has been possible to use IQNS and QENS to study protein folding and dynamics, giving detailed and unique insight into the kinds of transitions that unfolded and partially folded proteins undergo. These methods can also be used to understand how organisms and proteins adapt to living in extreme environments. To address these and other issues, a diverse set of neutron instruments, such as back scattering and spin-echo spectrometers, are needed. Again with the increased brightness that ESS offers, more accurate measurements will be feasible on far smaller biological samples than what was needed before.
Structure And Dynamics Of Biomembranes
Biological membranes are composed of complex lipids, glycolipids, and integral proteins that comprise the physical barrier between organelles and the extracellular environment from the cytosol. Membranes are involved in a wide range of functional and dynamic roles and mediate a number of physiologically relevant roles, such as trans membrane transport of nutrients and waste, maintaining ion gradients that drive a number of processes, and they are the mediators of xenobiotic efflux.
This last function is very important for the study of antibiotic resistant bacteria, a growing public health concern. In recent decades, the functional relationship between proteins and lipids has been explained by the existence of lipid rafts. There has been a lot of focus on the role of lipid composition and domain co-existence in the context of the cell membrane.
Methods that are used to study membrane structure and dynamics include SANS, neutron reflectometry, in combination with selective deuterium labeling. These approaches allow the observation of nuclear scattering length density profiles perpendicular to the membrane surface. This gives information about the internal functional organization of membrane proteins under physiological conditions.
Time-of-flight SANS and reflectometry can be used to study mechanisms of molecular interactions and transfer processes at biological interfaces. Neutron reflectometry studies of the anti-cancer and anti-HIV plant peptides showed how they aggregate and insert into the membrane. This is not possible with traditional X-ray or optical based methods, highlighting the unique and powerful niche that neutrons occupy.
With the proposed sophisticated suite of instrument at the ESS, it will be possible to measure a number of different length and time scales on a given biological membrane system, with smaller samples and higher time resolution. This will help scientists to better understand biochemical reactions are the membrane interface and will assist with the design of new therapeutic agents.
Biological imaging using neutrons is another area that will benefit greatly from the brightness of ESS. Neutrons, with their high penetrating power, absence of radiation damage to biological samples, and sensitivity to light atoms present in biological tissues/organisms, provide great opportunities for study in this field.
A landmark neutron imaging study looked at living plants and how they take up water through the root system. A recent study also looked at maize and switch grass in this non-invasive way. The results showed that it is possible to use neutron to determine root functionality, water uptake and redistribution in young plants, at sub-millimeter resolution. These living plants can be studied under natural conditions and can be observed through soil, a difficult feat with traditional optical imaging techniques.
Neutron imagining is complementary to NMR, X-ray, and gamma imaging techniques. With higher flux such studies will be more rapid and have improved time resolution.