ISSN:
1573-5001
Keywords:
Bacteriorhodopsin
;
Conformational exchange
;
Dynamics
;
Helix-helix interaction
;
Micelles
;
Relaxation
;
Spatial structure
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
,
Chemistry and Pharmacology
Notes:
Summary The backbone dynamics of uniformly 15N-labelled fragments (residues 1–71 and 1–36) of bacterioopsin, solubilized in two media (methanol-chloroform (1:1), 0.1 M 2HCO2NH4, or SDS micelles) have been investigated using 2D proton-detected heteronuclear 1H-15N NMR spectroscopy at two spectrometer frequencies, 600 and 400 MHz. Contributions of the conformational exchange to the transverse relaxation rates of individual nitrogens were elucidated using a set of different rates of the CPMG spin-lock pulse train and were essentially suppressed by the high-frequency CPMG spin-lock. We found that most of the backbone amide groups of (1–71)bacterioopsin in SDS micelles are involved in the conformational exchange process over a rate range of 103 to 104 s-1. This conformational exchange is supposed to be due to an interaction between two α-helixes of (1–71)bacterioopsin, since the hydrolysis of the peptide bond in the loop region results in the disappearance of exchange line broadening. 15N relaxation rates and 1H-15N NOE values were interpreted using the model-free approach of Lipari and Szabo [Lipari, G. and Szabo, A. (1982) J. Am. Chem. Soc., 104, 4546–4559]. In addition to overall rotation of the molecule, the backbone N-H vectors of the peptides are involved in two types of internal motions: fast, on a time scale 〈20 ps, and intermediate, on a time scale close to 1 ns. The intermediate dynamics in the α-helical stretches was mostly attributed to bending motions. A decrease in the order parameter of intermediate motions was also observed for residues next to Pro50, indicating an anisotropy of the overall rotational diffusion of the molecule. Distinctly mobile regions are identified by a large decrease in the order parameter of intermediate motions and correspond to the N- and C-termini, and to a loop connecting the α-helixes of (1–71)bacterioopsin. The internal dynamics of the α-helixes on the millisecond and nanosecond time scales should be taken into account in the development of a model of the functioning bacteriorhodopsin.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00211774
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