Detecting molecular fluctuations in biological samples

All biological molecules require some form of movement that is essential to their function. Molecules or parts of molecules show a wide range of vibrations ranging from several billion times a second (for example the movement of an amino acid within a protein) to movements of molecules over seconds (for example the rearrangement of elastic fibres in the aorta during a heartbeat). Measuring and observing such a wide range of molecular motions has been a difficult and challenging aspect of science and a full picture of molecular motion will only emerge eventually in the future by taking an interdisciplinary approach. One aspect of this approach that shows early promise is the technique of X-ray photon correlation spectroscopy. The interaction of X-rays with matter through diffraction and scattering is now the principal technique for molecular structure determination. The collection of data usually takes a period of seconds or even minutes and an 'average' picture of the molecular structure is observed. If it were possible to reduce the time required to collect the data, then it may be possible to view molecules as they move, this would give far more information about the mechanisms of biological processes than a static image ever could. These diffraction patterns taken at very rapid collection rates contain grainy images where their speckling is due to local fluctuations in structure, analysis of this speckling tells us about the motion of molecules within a tissue or a solution. One of the main challenges we need to overcome is the production of X-ray detectors that can collect and output data at a rate, which is comparable to the molecular motions that need to be investigated. The purpose of this project is to put together detectors developed by researchers involved in particle physics with projects devised by biological scientists. The project will optimise the possible use of current detectors and aim to study motion in a variety of molecules and tissues. To begin with, we shall focus on examining the movements of collagen, the most abundant protein in animals and also of economic importance in tissue engineering, wound healing and food industries. The molecular movements of collagen molecules in the millisecond to microsecond timescale are important for defining molecular structure and mechanical properties of this all important molecule. Researching the optimal way to use currently available X-ray detectors to record the dynamic processes within such samples will be a firm step toward using this technique for determining motion in a far wider range of tissues and molecules.

X-ray photon correlation spectroscopy is emerging as a technique capable of imaging dynamic processes in a variety of physical systems. The main effort in research has so far been in observation of slow diffusive processes in solutions of simple organic systems or hydrogels relevant to the physical sciences, however the technique could be developed to observe dynamic behaviour of molecules in the millisecond and microsecond timeframes, this gives access to important frequency modes in many biological tissues and has the advantage that specific dynamic processes could be observed within an intact tissue. The constraints on the time resolution lie mostly with the required development of detector technology, where readout time and photon efficiency need to be improved. This project has to be seen as a specific development within UK detector development, now focussed at RAL. We will match the capability of currently available detector technology with experiments on biological materials where the results from preliminary data will be meaningful to a wide range of researchers in the fields of biomaterials and macromolecular research. Detector development from RAL will provide the basis for recording diffracted photons giving direct dynamic observations of fibrillar assemblies of collagen. The equatorial region of the diffraction pattern describes the lateral packing of collagen molecules within a fibril. Our studies indicate that there is a temperature dependent liquid like disorder in the lateral packing, and we seek to observe the temperature dependent dynamics in this selected part of the diffraction pattern. The project planning will focus on developing the best match between the detector capability and the proposed experiment, this will form the technical basis for a series of experiments at synchrotron sources to measure the dynamics of collagen and if successful optimise the technology for other materials and macromolecules.