20– 22 Following the trigger, 2D IR spectra can be used to probe the resulting conformational changes to arbitrarily long times. Triggers include cis–trans isomerizations, conformational change, temperature or pH jumps, bond breakage, and other methods that induce conformational changes. 19ĢD IR spectroscopy can also be used to study kinetics longer than the intrinsic picosecond time resolution by triggering a conformational change. 18 It is a probable cause of amyloid polymorphs. 4 Structural heterogeneity is important in stability, such as side chains that stabilize protein structures. 12, 14– 17 Structural heterogeneity, by which we mean the populations of protein structures, plays a role in enzymes, since the active sites are very sensitive to geometry. 11– 13 Regarding the protein structures themselves, the 2D lineshapes reflect the distribution of protein structures in the ensemble, thereby providing a measure of structural heterogeneity. 7– 10 Hydration can be mapped in membrane proteins and ion channels and other biomolecular assemblies, such as DNA. Water and ion dynamics is critical for biological function and many researchers have utilized the picosecond dynamics of 2D IR spectroscopy to measure water structure in liquids and in biological systems. Collecting multiple 2D IR spectra as a function of time turns these static snapshots into a movie. 1, 6, 7 Thus, a 2D IR spectrum provides a snapshot of water and ion dynamics around static protein structures. About the only things that move on a 1 ps time scale are water molecules and ions as they make and break hydrogen bonds protein backbones are essentially fixed in space, as are side chains, on this picosecond time scale. With a subpicosecond time resolution, there is essentially no protein or biological structural change that is too fast for it to follow. 2D IR spectroscopy provides the ideal time resolution to measure structural change.
4, 5 Of course, for a technique to measure kinetics, the time resolution of the technique needs to be shorter than the time scale of structural change. 1– 3 Knowledge of the kinetics of the interconversion between members of a structural ensemble can lead to fundamental insights into the mechanisms of these processes. The structural evolution of proteins, designed to accomplish precise functions, is at the heart many processes in biology.
0 kommentar(er)
