TY - JOUR
AU - Saitô, Hazime
AB - Cross‐polarization and dipolar‐decoupled magic‐angle spinning 13C‐NMR spectra of [3‐13C]Ala‐labelled bacteriorhodopsin were obtained for hydrated purple membrane in the temperatures range 23°C to –110°C. Well‐resolved 13C‐NMR signals were observed either at ambient temperature or at –20°C but were broadened considerably at lower temperature below –40°C. This situation was interpreted in terms of the presence of exchange processes with a rate constant of 102 S−1 at ambient temperature among several conformations slightly different from each other. We found that such an exchange process was strongly influenced by the manner of organization of the lipid bilayers depending upon the presence or absence of cations responsible for electric shielding of negative charge at the polar head groups. The manner of organization of the lipid bilayers was conveniently characterized by a characteristic temperature at which the methyl peaks of fatty acyl groups of lipids in the purple membrane were suppressed due to interference of motional frequency with the decoupling frequency (10–100 kHz) for preparations containing 10 mM NaCl or CaCl2. No such spectral change in the absence of these cations was noted even if a preparation was cooled to –110°C. The secondary structures of [3‐13C]Ala‐labelled bacteriorhodopsin was not always identical at temperatures between ambient and low temperatures, since the 13C chemical shifts and relative peak intensities for purple membrane preparations containing these salts changed with temperature in the range –110°C to 23°C. In particular, we found that some residues involving Ala residues at the αII‐helix and loop region were converted at temperatures below –60°C to a conformation involving αI‐helix. In other words, some portion of the α‐helical conformation of bacteriorhodopsin proposed from results obtained by cryoelectron microscopy, at very low temperatures, is not always retained at ambient temperature.
TI - Temperature‐Dependent Conformational Change of Bacteriorhodopsin as Studied by Solid‐State 13C NMR
JF - FEBS Journal
DO - 10.1111/j.1432-1033.1996.0294u.x
DA - 1996-07-01
UR - https://www.deepdyve.com/lp/wiley/temperature-dependent-conformational-change-of-bacteriorhodopsin-as-0LV6fD0xQE
SP - 294
EP - 301
VL - 239
IS - 2
DP - DeepDyve
ER -