Biophysics of proteins
Professor
Office: Room 55 Chemistry and Biochemistry Building
Lab: Room 46 Chemistry and Biochemistry Building
P.O. Box 173400
Bozeman, MT 59717
Ph: 406 994 5414
Fax: 406 994 5407
pcallis montana.edu
Research Group: http://www.chemistry.montana.edu/callis
B.S. Oregon State University, Corvallis, Oregon
Ph.D. in Physical Chemistry, University of Washington, 1965
N.I.H. Postdoctoral Fellow, Cal Tech, 1966-68
Courses:
· CHMY 564 ADVANCED QUANTUM CHEMISTRY
· CHMY 361 ELEMENTS OF PHYSICAL CHEMISTRY
· CHMY 373 PHYSICAL CHEMISTRY II
Awards:
Wiley Award for Meritorious Research, 1990
Cox Award for Teaching and Scholarship, 1992
Phi Kappa Phi Anna Krueger Fridley Award for Distinguished Teaching, 1994
Callis Group Overview
We are currently studying the internal structure and dynamics of proteins through hybrid quantum mechanics-molecular dynamics (QM-MM) simulations and ultraviolet spectroscopy. Our computations are closely coupled to a vast database of UV fluorescence quenching through electron transfer. These electron transfer rates a extremely sensitive to local electrostatic. The results should be transferable for use in understanding mechanisms of enzyme action, molecular recognition, and ground state redox reactions.
Keywords:
Biophysical, Spectroscopy
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.
1. We continue to pursue stronger documentation of the precise nature of the charge transfer state on the amide through higher level quantum calculations.
2. We continue to apply our method to test and predict Trp fluorescence in a growing array of proteins.
3. We are refining similar predictions for quenching caused by other protein residues, including protonated histidine, disulfide, amide side chains, and cysteine.
4. We are studying the nature of the electron transfer quantum mechanical matrix element, which is a major factor in the quenching process.
Selected Publications
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
Keywords:
Biophysical, Protein Chemistry
Quantitative prediction of fluorescence quantum yields in proteins: Flavins and dyes
Oxidized flavin cofactors exhibit an even wider range of fluorescence intensities and lifetimes than tryptophan. The source of this quenching is better understood: flavin quenching is almost always by electron transfer from nearby unexcited tryptophan and tyrosine to the excited state of the flavin. The same appears to be the case for many of the fluorescent dyes that are attached to proteins for various imaging and diagnostic purposes. We are modeling the efficiency of this process with the same tools we use for modeling Trp fluorescence.
Selected Publications
Callis PR, Liu T :
Short Range Photoinduced Electron Transfer in Proteins: QM-MM Simulations of Tryptophan and Flavin Fluorescence Quenching in Proteins
Chemi Phys. (2006) in press+A60+A25
Keywords:
Biophysical, Protein Chemistry
Quantitative prediction of fluorescence spectra and spectral relaxation of tryptophan in proteins.
The tryptophan fluorescence spectrum in proteins depends sensitively on the local environment covering the range 308-355 nm. We have previously shown that the wavelength can be predicted from QM-MM simulations. One must sum over all charged atoms of the protein and solvent to find the electric potential different from the 5- to the 6-membered ring of the Trp. Recently, there is considerable interesting in how rapidly the solvent and protein environment responds to the suddent large dipole increase caused by excitation of Trp. We are modelling the dynamics of this shift with our QM-MM simulations to see why controversial, long relaxation times appear in some experiments.
Selected Publications
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)
Vivian JT, Callis PR:
Mechanisms of Tryptophan Fluorescence Shifts in Proteins
Biophys. J. 80 2093-2109 (2001)
Keywords:
Biophysical
· View All Publications
|
