Optical control of the primary step of photoisomerization of the retinal molecule in bacteriorhodopsin from the all-trans to the 13-cis state was demonstrated under weak field conditions (where only 1 of 300 retinal molecules absorbs a photon during the excitation cycle) that are relevant to understanding biological processes. By modulating the phases and amplitudes of the spectral components in the photoexcitation pulse, we showed that the absolute quantity of 13-cis retinal formed upon excitation can be enhanced or suppressed by +/-20% of the yield observed using a short transform-limited pulse having the same actinic energy. The shaped pulses were shown to be phase-sensitive at intensities too low to access different higher electronic states, and so these pulses apparently steer the isomerization through constructive and destructive interference effects, a mechanism supported by observed signatures of vibrational coherence. These results show that the wave properties of matter can be observed and even manipulated in a system as large and complex as a protein.

Bacteriorhodopsin-like proteins provide archaea and eubacteria with a unique bioenergetic pathway comprising light-driven transmembrane proton translocation by a single retinal-binding protein.Recently, homologous proteins were found to perform photosensory functions in lower eukaryotes, but no active ion transport by eukaryotic rhodopsins was detected. By demonstrating lightdriven proton pumping in a fungal rhodopsin from Leptosphaeria maculans, we present a case of a retinal-based proton transporter from a eukaryote. This result implies that in addition to oxidative phosphorylation and chlorophyll photosynthesis, some lower eukaryotes may have retained the archaeal route of building an electrochemical transmembrane gradient of protons.proton transport ͉ sensory rhodopsins

Alzheimer's disease pathology has demonstrated amyloid plaque formation associated with plasma membranes and the presence of intracellular amyloid-␤ (A␤) accumulation in specific vesicular compartments. This suggests that lipid composition in different compartments may play a role in A␤ aggregation. To test this hypothesis, we have isolated cellular membranes from human brain to evaluate A␤40/42-lipid interactions. Plasma, endosomal, lysosomal, and Golgi membranes were isolated using sucrose gradients. Electron microscopy demonstrated that A␤ fibrillogenesis is accelerated in the presence of plasma and endosomal and lysosomal membranes with plasma membranes inducing an enhanced surface organization. Alternatively, interaction of A␤ with Golgi membranes fails to progress to fibril formation, suggesting that A␤-Golgi head group interaction stabilizes A␤. Fluorescence spectroscopy using the environment-sensitive probes 1,6-diphenyl-1,3,5-hexatriene, laurdan, N-⑀-dansyl-L-lysine, and merocyanine 540 demonstrated variations in the inherent lipid properties at the level of the fatty acyl chains, glycerol backbone, and head groups, respectively. Addition of A␤40/42 to the plasma and endosomal and lysosomal membranes decreases the fluidity not only of the fatty acyl chains but also the head group space, consistent with A␤ insertion into the bilayer. In contrast, the Golgi bilayer fluidity is increased by A␤40/42 binding which appears to result from lipid head group interactions and the production of interfacial packing defects.Alzheimer's disease is an age-related disorder that is characterized by progressive cognitive decline and neurodegeneration (1, 2). Pathological examinations have demonstrated that one of the key features is the presence of amyloid plaques associated with neuritic degeneration. Senile plaques are composed predominantly of a 40 -42-residue peptide, amyloid-␤ (A␤40/42). The development of Alzheimer's disease pathology has been proposed to be the result of A␤ 1 deposition in association with membrane structures. Recent studies have demonstrated that plaque formation may be initiated in a plasma membrane form (3, 4) and that A␤ deposition in aged dogs is associated with the extracellular leaflet of the plasma membrane (5). Furthermore, the intracellular accumulation of A␤ in lysosomal or late endosomal vesicles in vitro suggest that these compartments may be involved in neurotoxicity (6 -9). A␤ is generated from the proteolytic cleavage of the amyloid precursor protein in the endoplasmic reticulum to generate A␤42 and the trans-Golgi network to generate A␤40 (10 -14). It has also been suggested that A␤40/42 may also be generated at the plasma membrane surface. The presence of A␤ in distinct compartments and the proposal that lipid association is important for both neurotoxicity and fibrillogenesis suggest that the lipid composition and characteristics of these compartments may play vital roles in the disease process. Previous studies (15,16) have demonstrated accumulation of A␤42 in lysosomal compartm...

Neurospora rhodopsin (NR, also known as NOP-1) is the first rhodopsin of the haloarchaeal type found in eucaryotes. NR demonstrates a very high degree of conservation of the amino acids that constitute the proton-conducting pathway in bacteriorhodopsin (BR), a light-driven proton pump of archaea. Nevertheless, NR does not appear to pump protons, suggesting the absence of the reprotonation switch that is necessary for the active transport. The photocycle of NR is much slower than that of BR, similar to the case of pharaonis phoborhodopsin (ppR), an archaeal photosensory protein. The functional and photochemical differences between NR and BR should be explained in the structural context. In this paper, we studied the structural changes of NR following retinal photoisomerization by means of low-temperature Fourier transform infrared (FTIR) spectroscopy and compared the obtained spectra with those for BR. For the spectroscopic analysis, we established the light-adaptation procedure for NR reconstituted into 1,2-dimyristoyl-sn-glycero- 3-phosphocholine/1,2-dimyristoyl-sn-glycero-3-phosphate (DMPC/DMPA) liposomes, which takes approximately 2 orders of magnitudes longer than in BR. The structure of the retinal chromophore and the hydrogen-bonding strength of the Schiff base in NR are similar to those in BR. Unique spectral features are observed for the S-H stretching vibrations of cysteine and amide-I vibrations for NR before and after retinal isomerization. In NR, there are no spectral changes assignable to the amide bands of alpha helices. The most prominent difference between NR and BR was seen for the water O-D stretching vibrations (measured in D(2)O). Unlike for haloarchaeal rhodopsins such as BR and ppR, no O-D stretches of water under strong hydrogen-bonded conditions (<2400 cm(-1)) were observed in the NR(K) minus NR difference spectra. This suggests a unique hydrogen-bonded network of the Schiff base region, which may be responsible for the lack of the reprotonation switch in NR.