Scientific Opportunities: Life Sciences
Structure and Dynamics in Solutions and Membranes
However, the central question in biophysics still remains: What is the connection between the structure and function of biological macromolecules such as proteins, DNA, RNA, polysaccharides, and their complexes? Answering this question requires understanding the dynamics of macromolecular structures in their natural environment, where flexibility of the molecules and water, pH, and ion concentration play determinant roles. Examples include protein and nucleic acid folding and unfolding, polymer collapse upon change of solvent, electron transfer, and large-scale fluctuations in macromolecules.
Studies of the structure and dynamics of molecules in solutions and membranes are an essential complement to macromolecular crystallography. Such studies are poised to provide new insights into the function, control, and dynamics of individual macromolecules and large molecular complexes. Solutions and membranes are the media where many of the most intriguing and complex biological processes take place, including molecular recognition, signal transduction, chemical sensing, transport, synthesis, degradation, replication, and defense.
The high brightness of NSLS-II will give x-ray scattering and spectroscopy studies of biomolecules and membranes unparalleled sensitivity and time resolution, enabling more precise structure determinations and extending measurements of dynamics down to the microsecond time range.
The time scale of the folding process varies from picoseconds to nanoseconds (when the initial secondary structure starts to form) to milliseconds to seconds (when the folding process is completed). With the development of more accurate force fields that simulate the interactions that govern the folding process, and construction of more powerful computers, computational biologists are lengthening their calculations to the time scale of microseconds. The high brightness of NSLS-II will extend the time resolution of solution-scattering measurements down to this time scale. Computations and experiments will then overlap and provide better tests of our understanding of the physics of the underlying interactions.
Structural Kinetics in Biological Macromolecular Complexes
In contrast, small angle solution scattering can provide structural information that reveals global conformation changes in biomolecules and molecular complexes in solution, and is thus complementary to protein crystallography. Solution scattering is an effective technique for determining the low-resolution, basic shape of these complexes (see figure). This approach also holds great potential for resolving the structural kinetics of macromolecular complexes using time resolved solution scattering to produce low-resolution movies of events such as the assembly and operation of molecular machines.
The high brightness of NSLS-II will provide high intensity, highly collimated, and small x-ray beams, resulting in high quality data necessary for accurate shape determinations. NSLS-II will also enable time resolved measurements at microsecond time resolutions.
Extending Solution Scattering to Membrane Proteins
All of the solution scattering techniques used for proteins are equally applicable to the 2D liquid of membrane proteins, including low-resolution shape determination and time resolved measurement. The high brightness of NSLS-II will enable solution scattering experiments to provide information about these structural transitions. These phenomena are related directly to the function of the membrane proteins, and therefore are central to many branches of life-science research.
Study of Metalloproteins with X-ray Absorption Spectroscopy
Traditionally, XAS, like most other spectroscopies, has been used as a static probe of structure. NSLS-II provides the opportunity to extend x-ray absorption measurements into the time-resolved realm, potentially revolutionizing the study of biochemical and bioinorganic systems. For example, proteins containing metal, called metalloproteins (hemoglobin is an example), react over extremely quick time scales - sometimes as fast as a picosecond. NSLS II will allow much faster time scales to be probed than XAS is currently capable of.
Electron Delocalization in Biomolecules
As an example, consider the light harvesting complex (LHC) protein-chromophore (see figure) of the photosynthetic bacterium rhodobacter sphaeroides. Light is first absorbed by a circular aggregate of bacteriochlorophyll molecules and carotenoids held together by proteins, LH-II. Energy is then transferred to a circular antenna complex, LH-I, surrounding the reaction center, and finally to the reaction center (RC) where it starts the respiratory cycle of the cell. The structures of LH-II and RC are known to atomic resolution from x-ray diffraction experiments. However, the mechanism and dynamics of electron energy transfer remains a mystery.
The high brightness and flux of NSLS-II, together with new optical schemes, will enable inelastic x-ray experiments that will open new windows into the electronic properties of biomolecules.
Last Modified: April 2, 2013