title: Translational diffusion of fluorescent proteins by molecular fourier imaging correlation spectroscopy.
abstract: The ability to noninvasively observe translational diffusion of proteins and protein complexes is important to many biophysical problems. We report high signal/noise (>or=250) measurements of the translational diffusion in viscous solution of the fluorescent protein, DsRed. This is carried out using a new technique: molecular Fourier imaging correlation spectroscopy (M-FICS). M-FICS is an interferometric method that detects a collective Fourier component of the fluctuating density of a small population of fluorescent molecules, and provides information about the distribution of molecular diffusivities. A theoretical analysis is presented that expresses the detected signal fluctuations in terms of the relevant time-correlation functions for molecular translational diffusion. Furthermore, the role played by optical orientational degrees of freedom is established. We report Fickian self-diffusion of the DsRed tetramer at short timescales. The long-time deviation of our data from Fickian behavior is used to determine the variance of the distribution of the protein self-diffusion coefficient. We compare our results to the expected outcomes for 1), a bi-disperse distribution of protein species, and 2), dynamic disorder of the host solvent.
authors.affiliation: Department of Chemistry, Institute of Theoretical Sciences, University of Oregon, Eugene, USA.
authors.forename: Michael C
authors.initials: MC
authors.lastname: Fink
authors.forename: Kenneth V
authors.initials: KV
authors.lastname: Adair
authors.forename: Marina G
authors.initials: MG
authors.lastname: Guenza
authors.forename: Andrew H
authors.initials: AH
authors.lastname: Marcus
mesh_terms: D005455:Fluorescent Antibody Technique / Q000379:methods*; D005456:Fluorescent Dyes; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D008856:Microscopy, Fluorescence / Q000379:methods*; D015336:Molecular Probe Techniques; D021381:Protein Transport / Q000502:physiology*; D017550:Spectroscopy, Fourier Transform Infrared / Q000379:methods*
chemical_list: D005456:Fluorescent Dyes