H. Kandori et al., Local and distant protein structural changes on photoisomerization of the retinal in bacteriorhodopsin, P NAS US, 97(9), 2000, pp. 4643-4648
Citations number
34
Categorie Soggetti
Multidisciplinary
Journal title
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
The photoisomerization of the retinal in bacteriorhodopsin is selective and
efficient and yields perturbation of the protein structure within femtosec
onds. The stored light energy in the primary intermediate is then used for
the net translocation of a proton across the membrane in the microsecond to
millisecond regime. This study is aimed at identifying how the protein cha
nges on photoisomerization by using the O-H groups of threonines as interna
l probes. Polarized Fourier-transform IR spectroscopy of [3-O-18]threonine-
labeled and unlabeled bacteriorhodopsin indicates that 3 of the threonines
(of a total of 18) change their hydrogen bonding. One is exchangeable in D2
O, but two are not. A comprehensive mutation study indicates that the resid
ues involved are Thr-89, Thr-17, and Thr-121 (or Thr-90). The perturbation
of only three threonine side chains suggests that the structural alteration
at this stage of the photocycle is local and specific. Furthermore, the st
ructural change of Thr-17, which is located >11 A from the retinal chromoph
ore, implicates a specific perturbation channel in the protein that accompa
nies the retinal motion.