Premium
Unfolding pathways of native bacteriorhodopsin depend on temperature
Author(s) -
Janovjak Harald,
Kessler Max,
Oesterhelt Dieter,
Gaub Hermann,
Müller Daniel J.
Publication year - 2003
Publication title -
the embo journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 7.484
H-Index - 392
eISSN - 1460-2075
pISSN - 0261-4189
DOI - 10.1093/emboj/cdg509
Subject(s) - bacteriorhodopsin , force spectroscopy , crystallography , protein secondary structure , biophysics , transmembrane protein , molecule , biology , protein structure , unfolded protein response , membrane , chemical physics , chemistry , biochemistry , endoplasmic reticulum , receptor , organic chemistry
The combination of high‐resolution atomic force microscopy (AFM) imaging and single‐molecule force‐spectroscopy was employed to unfold single bacteriorhodopsins (BR) from native purple membrane patches at various physiologically relevant temperatures. The unfolding spectra reveal detailed insight into the stability of individual structural elements of BR against mechanical unfolding. Intermittent states in the unfolding process are associated with the stepwise unfolding of α‐helices, whereas other states are associated with the unfolding of polypeptide loops connecting the α‐helices. It was found that the unfolding forces of the secondary structures considerably decreased upon increasing the temperature from 8 to 52°C. Associated with this effect, the probability of individual unfolding pathways of BR was significantly influenced by the temperature. At lower temperatures, transmembrane α‐helices and extracellular polypeptide loops exhibited sufficient stability to individually establish potential barriers against unfolding, whereas they predominantly unfolded collectively at elevated temperatures. This suggests that increasing the temperature decreases the mechanical stability of secondary structural elements and changes molecular interactions between secondary structures, thereby forcing them to act as grouped structures.