title: The "long tail" of the protein tumbling correlation function: observation by (1)H NMR relaxometry in a wide frequency and concentration range.
abstract: Inter-protein interactions in solution affect the auto-correlation function of Brownian tumbling not only in terms of a simple increase of the correlation time, they also lead to the appearance of a weak slow component ("long tail") of the correlation function due to a slowly changing local anisotropy of the microenvironment. The conventional protocol of correlation time estimation from the relaxation rate ratio R1/R2 assumes a single-component tumbling correlation function, and thus can provide incorrect results as soon as the "long tail" is of relevance. This effect, however, has been underestimated in many instances. In this work we present a detailed systematic study of the tumbling correlation function of two proteins, lysozyme and bovine serum albumin, at different concentrations and temperatures using proton field-cycling relaxometry combined with R1ρ and R2 measurements. Unlike high-field NMR relaxation methods, these techniques enable a detailed study of dynamics on a time scale longer than the normal protein tumbling correlation time and, thus, a reliable estimate of the parameters of the "long tail". In this work we analyze the concentration dependence of the intensity and correlation time of the slow component and perform simulations of high-field (15)N NMR relaxation data demonstrating the importance of taking the "long tail" in the analysis into account.
authors.affiliation: Institut für Physik, Martin-Luther-Universität Halle-Wittenberg, Betty-Heimann-Str. 7, 06120, Halle, Germany.
authors.forename: Matthias
authors.initials: M
authors.lastname: Roos
authors.affiliation: Universität Bayreuth, Lehrstuhl Experimentalphysik II, Universitätsstr. 30, 95440, Bayreuth, Germany.
authors.forename: Marius
authors.initials: M
authors.lastname: Hofmann
authors.affiliation: Institut für Physik, Martin-Luther-Universität Halle-Wittenberg, Betty-Heimann-Str. 7, 06120, Halle, Germany.
authors.forename: Susanne
authors.initials: S
authors.lastname: Link
authors.affiliation: Institut für Physik, Martin-Luther-Universität Halle-Wittenberg, Betty-Heimann-Str. 7, 06120, Halle, Germany.
authors.forename: Maria
authors.initials: M
authors.lastname: Ott
authors.affiliation: Institut für Physik, Martin-Luther-Universität Halle-Wittenberg, Betty-Heimann-Str. 7, 06120, Halle, Germany.
authors.forename: Jochen
authors.initials: J
authors.lastname: Balbach
authors.affiliation: Universität Bayreuth, Lehrstuhl Experimentalphysik II, Universitätsstr. 30, 95440, Bayreuth, Germany.
authors.forename: Ernst
authors.initials: E
authors.lastname: Rössler
authors.affiliation: Institut für Physik, Martin-Luther-Universität Halle-Wittenberg, Betty-Heimann-Str. 7, 06120, Halle, Germany. kay.saalwaechter@physik.uni-halle.de.
authors.forename: Kay
authors.initials: K
authors.lastname: Saalwächter
authors.affiliation: Institut für Physik, Martin-Luther-Universität Halle-Wittenberg, Betty-Heimann-Str. 7, 06120, Halle, Germany. krushelnitsky@physik.uni-halle.de.
authors.forename: Alexey
authors.initials: A
authors.lastname: Krushelnitsky
mesh_terms: D000818:Animals; D030161:Avian Proteins / Q000737:chemistry*; D002645:Chickens; D017666:Deuterium Oxide / Q000737:chemistry; D009113:Muramidase / Q000737:chemistry*; D019906:Nuclear Magnetic Resonance, Biomolecular / Q000379:methods; D011487:Protein Conformation; D012996:Solutions; D012997:Solvents / Q000737:chemistry
chemical_list: D030161:Avian Proteins; D012996:Solutions; D012997:Solvents; D009113:Muramidase; D017666:Deuterium Oxide
keywords: Brownian tumbling; Correlation function; Field-cycling; Inter-protein interactions; Relaxation