title: Terbium luminescence-lifetime heterogeneity and protein equilibrium conformational dynamics.
abstract: The fluorescence decay of the rare earth terbium when bound to the protein calmodulin changes from a simple exponential decay to a complex nonexponential decay as the temperature is lowered below 200 K. We have fit the observed decay curves by assuming that the terbium emission is a forced electric dipole transition and proteins have a distribution of continuous conformational states. Quantitative fits to the data indicate that the root-mean-square configurational deviation of the atoms surrounding the terbium ion is 0.2 A, in good agreement with other measurements. We further point out that because the protein seems to undergo a glass transition yet retains configurational order at room temperature, the proper name for the physical state of a protein at room temperature is the rubber-like state.
authors.forename: R H
authors.initials: RH
authors.lastname: Austin
authors.forename: D L
authors.initials: DL
authors.lastname: Stein
authors.forename: J
authors.initials: J
authors.lastname: Wang
mesh_terms: D002147:Calmodulin; D008163:Luminescent Measurements; D011487:Protein Conformation; D013696:Temperature; D013725:Terbium
chemical_list: D002147:Calmodulin; D013725:Terbium