Quantitative prediction of fluorescence quantum yields in proteins: Tryptophan
Tryptophan fluorescence intensity is widely used to monitor almost any imaginable change in protein structure. Tryptophan fluorescence intensity is widely used to monitor almost any imaginable change in protein structure. Using hybrid quantum mechanics-molecular mechanics (QM-MM) simulations we have recently shown that the full 30-fold range of Trp fluorescence quantum yields (and lifetimes) observed in proteins is due primarily to different rates of electron transfer from the excited indole ring to one of two nearest backbone amides. This heretofore puzzling dependence on protein environment arises mainly from the average local electric potential difference between the Trp ring and acceptor amide and from the amplitude of potential difference fluctuation caused by protein and solvent motions.
- We continue to pursue stronger documentation of the precise nature of the charge transfer state on the amide through higher level quantum calculations.
- We continue to apply our method to test and predict Trp fluorescence in a growing array of proteins.
- We are refining similar predictions for quenching caused by other protein residues, including protonated histidine, disulfide, amide side chains, and cysteine.
- We are studying the nature of the electron transfer quantum mechanical matrix element, which is a major factor in the quenching process.
Callis PR, Liu T, "Quantitative predictions of fluorescence quantum yields for tryptophan in proteins ." J. Phys. Chem. B 108 4248-4259 (2004)
Xu J, Toptygin D, Graver KJ, Albertini RA, Savtchenko RS, Meadow ND, Roseman S, Callis PR, Brand L, Knutson JR , "Ultrafast Fluorescence Dynamics of Tryptophan in theProteins Monellin and IIAGlc." J. Am. Chem. Soc. 128 ASAP (2006)
Callis PR, Vivian JT, "Understanding the variable fluorescence quantum yield of tryptophan in proteins using QM-MM simulations. Quenching by charge transfer to the peptide backbone." Chem. Phys. Letters 369 409-414 (2003)+A49
Biophysical, Protein Chemistry