Shedding light on biomolecule conformational dynamics using fluorescence measurements of trapped ions.
Biomolecule conformational change has been widely investigated in solution using several methods; however, much less experimental data about structural changes are available for completely isolated, gas-phase biomolecules. Studies of conformational change in unsolvated biomolecules are required to complement the interpretation of mass spectrometry measurements and in addition, can provide a means to directly test theoretical simulations of biomolecule structure and dynamics independent of a simulated solvent. In this Feature Article, we review our recent introduction of a fluorescence-based method for probing local conformational dynamics in unsolvated biomolecules through interactions of an attached dye with tryptophan (Trp) residues and fields originating on charge sites. Dye-derivatized biomolecule ions are formed by electrospray ionization and are trapped in a variable-temperature quadrupole ion trap in which they are irradiated with either continuous or short pulse lasers to excite fluorescence. Fluorescence is measured as a function of temperature for different charge states. Optical measurements of the dye fluorescence include average intensity changes, changes in the emission spectrum, and time-resolved measurements of the fluorescence decay. These measurements have been applied to the miniprotein, Trp-cage, polyproline peptides and to a beta-hairpin-forming peptide, and the results are presented as examples of the broad applicability and utility of these methods. Model fits to Trp-cage fluorescence data measured as a function of temperature provide quantitative information on the thermodynamics of conformational changes, which are reproduced well by molecular dynamics. Time-resolved measurements of the fluorescence decays of Trp-cage and small polyproline peptides definitively demonstrate the occurrence of fluorescence quenching by the amino acid Trp in unsolvated biomolecules.
Iavarone
Anthony T
AT
The Rowland Institute at Harvard, 100 Edwin H. Land Boulevard, Cambridge, MA 02142, USA.
Duft
Denis
D
Parks
Joel H
JH
D005453:Fluorescence; D005456:Fluorescent Dyes / Q000737:chemistry*; D007477:Ions; D007834:Lasers; D008968:Molecular Conformation; D036103:Nanotechnology; D010455:Peptides / Q000737:chemistry*; D013050:Spectrometry, Fluorescence / Q000295:instrumentation; D021241:Spectrometry, Mass, Electrospray Ionization / Q000295:instrumentation / Q000379:methods; D014364:Tryptophan / Q000737:chemistry*
D005456:Fluorescent Dyes; D007477:Ions; D010455:Peptides; C508725:Trp-cage peptide; D014364:Tryptophan