Energy transfer spectroscopic ruler

These and other workers(46) have proposed that the energy transfer process can serve as a spectroscopic ruler (10-60 A) in biological systems. 

Stryer, L. (1978). Fluorescence energy transfer as a spectroscopic ruler. Annu. Rev. Biochem. 47, 819—46. 

The use of Forster non-radiative energy transfer for measuring distances at a supramolecular level (spectroscopic ruler) will be discussed in detail in Chapter 9. 

The Forster resonance energy transfer can be used as a spectroscopic ruler in the range of 10-100 A. The distance between the donor and acceptor molecules should be constant during the donor lifetime, and greater than about 10 A in order to avoid the effect of short-range interactions. The validity of such a spectroscopic ruler has been confirmed by studies on model systems in which the donor and acceptor are separated by well-defined rigid spacers. Several precautions must be taken to ensure correct use of the spectroscopic ruler, which is based on the use of Eqs (9.1) to (9.3) ... 

Chapter 9 is devoted to resonance energy transfer and its applications in the cases of donor-acceptor pairs, assemblies of donor and acceptor, and assemblies of like fluorophores. In particular, the use of resonance energy transfer as a spectroscopic ruler , i.e. for the estimation of distances and distance distributions, is presented. 

Energy transfer has been used extensively in biological work as a spectroscopic ruler (45 1 and in numerous other studies1-46" the underlying assumption being that the Forster expressions are valid in all situations. 

Stryer L, Haugland RP (1967) Energy transfer a spectroscopic ruler. Proc Nat Acad Sci USA 58 719-726... 

L. Stryer, Fluorescence Energy Transfer as a Spectroscopic Ruler, Annu. Rev. Biochem. 1978,47, 819 C. Berney and G. Danuser, FRET or No FRET A Quantitative Comparison, Biophys. J. 2003, 84, 3992 http //www.probes.com/ handbook/. 

Forster s theory [1], has enabled the efficiency of EET to be predicted and analyzed. The significance of Forster s formulation is evinced by the numerous and diverse areas of study that have been impacted by his paper. This predictive theory was turned on its head by Stryer and Haugland [17], who showed that distances in the range of 2-50 nm between molecular tags in a protein could be measured by a spectroscopic ruler known as fluorescence resonance energy transfer (FRET). Similar kinds of experiments have been employed to analyze the structure and dynamics of interfaces in blends of polymers. 

L. Stryer and R. Haugland, Energy transfer A spectroscopic ruler, Proc. Natl. Acad. Sci. USA 58, 719 (1967). 

The distance scale on which FRET occurs makes the technique very attractive in the life sciences because it corresponds well to relevant distances in biology for example, the distance between base pairs in double-stranded DNA is 0.3 nm. The potential of FRET to reveal proximity in biological macro molecules was already pointed out in 1967 by Stryer and Haugland in their article Energy Transfer A Spectroscopic Ruler [98]. In their pioneering experiment, they labeled poly-pro-line peptides of different lengths at both ends and demonstrated the R dependence of the energy-transfer efficiency. Today, FRET is a weU-established spectroscopic technique [57, 58]. For a review, see the article by Selvin [99]. 

Table III summarizes rate, helicity, and donor-acceptor distance data for the 16-mer bundle. Because of the observable trend in conformation versus rate in the electron transfer studies, it was decided to measure donor-acceptor distances in the 16-mer metalloprotein bundles. In order to study the effects of solution conditions on H, the donor-acceptor distance, Forster energy transfer was used as a spectroscopic ruler, according to...

Fluorescence resonance energy transfer (FRET) experiments commonly use the fluorescent spectrum and relaxation times of the Forster donor and acceptor chromophores to find the distances between fluorescent dyes at labeled sites in protein, DNA, RNA, etc. FRET is a type of spectroscopic ruler . The computation uses either experimental quantum yields or relaxation lifetimes to calculate the efficiency of resonance energy transfer Ej. 

The FRET efficiency, E, is given by Eq. 6 and is the ratio of the rate of FRET to all processes that depopulate the donor excited state [3]. From Eq. 2, the FRET efficiency reduces to a function of the Forster distance, Rq, and donor-acceptor separation, r. The relative distance dependence of FRET, E vs. r/Ro, is illustrated in Fig. Id. At donor-acceptor separations equal to the Forster distance, r = Rq, the energy transfer efficiency is = 50 %. It can also be seen that, for O.SRq FRET efficiency is very sensitive to the donor-acceptor separation and can serve as a spectroscopic molecular ruler to accurately measure distances at the biomolecular length scale. 

---