Biology subjects

Morigaki, K.

Publications and source records attributed to Morigaki, K..

3 recordsLinked to original sources

bioRxiv2022

Enhancing the spectral range of plant and bacterial Light-Harvesting pigment-protein complexes with various synthetic chromophores incorporated into lipid vesicles

The Light-Harvesting (LH) pigment-protein complexes found in photosynthetic organisms have the role of absorbing solar energy with high efficiency and transferring it to reaction centre complexes. LH complexes contain a suite of pigments that each absorb light at specific wavelengths, however, the natural combinations of pigments within any one protein complex do not cover the full range of solar radiation. Here, we provide an in-depth comparison of the relative effectiveness of five different organic "dye" molecules (Texas Red, ATTO, Cy7, Dil, DiR) for enhancing the absorption range of two different LH membrane protein complexes (the major LHCII from plants and LH2 from purple phototrophic bacteria). Proteoliposomes were self-assembled from defined mixtures of lipids, proteins and dye molecules and their optical properties were quantified by absorption and fluorescence spectroscopy. Both lipid-linked dyes and alternative lipophilic dyes were found to be effective excitation energy donors to LH protein complexes, without the need for direct chemical or generic modification of the proteins. The Forster theory parameters (e.g., spectral overlap) were compared between each donor-acceptor combination and found to be good predictors of an effective dye-protein combination. At the highest dye-to-protein ratios tested (over 20:1), the effective absorption strength integrated over the full spectral range was increased to ~180% of its natural level for both LH complexes. Lipophilic dyes could be inserted into pre-formed membranes although their effectiveness was found to depend upon favourable physicochemical interactions. Finally, we demonstrated that these dyes can also be effective at increasing the spectral range of surface-supported models of photosynthetic membranes, using fluorescence microscopy. The results of this work provide insight into the utility of self-assembled lipid membranes and the great flexibility of LH complexes for interacting with different dyes.

biophysics↗

bioRxiv2020

Understanding the photophysics and structural organization of photosynthetic proteins using model lipid membranes assembled from natural plant thylakoids

The light-harvesting (LH) biomembranes from photosynthetic organisms perform solar energy absorption and transfer with high efficiency. There is great interest in the nanoscale biophysics of photosynthesis, however, natural membranes are complex and highly curved so can be challenging to study. Here we present model photosynthetic "hybrid membranes" assembled from a combination of natural LH membranes and synthetic lipids deposited into a patterned polymerized lipid template on glass. This arrangement offers many advantages over previous model systems including: a sufficiently complex mixture of natural proteins to mimic the biological processes, a modular self-assembly mechanism, and a stabilizing template promoting the formation of supported lipid bilayers from complex natural membranes with high protein content (that would not otherwise form). These hybrid membranes can be used as a platform to delineate the complex relationship between LH energy pathways and membrane organization. Atomic force microscopy and fluorescence lifetime microscopy revealed that hybrid membranes have an elongated fluorescence lifetime ([~]4 ns) compared to native membranes ([~]0.5 ns), a direct consequence of reduced protein density and an uncoupling of protein-protein interactions. We observed the real time self-assembly and migration of LH proteins from natural membrane extracts into the hybrid membranes and monitored the photophysical state of the membranes at each stage. Finally, experiments utilizing our hybrid membranes suggest that assays currently used in the photosynthesis community to test the electron transfer activity of Photosystem II may have non-specific interactions with other proteins, implying that new methods are needed for reliable quantification of electron transfers in photosynthesis.

biophysics↗

bioRxiv2019

Affinity of rhodopsin to raft enables the aligned oligomer formation from dimers: Coarse-grained molecular dynamics simulation of disk membranes

The visual photopigment protein rhodopsin (Rh) is a typical G protein-coupled receptor (GPCR) that initiates the phototransduction cascade in retinal disk membrane of rod-photoreceptor cells. Rh molecule has a tendency to form dimer, and the dimer tends to form rows, which is suggested to heighten phototransduction efficiency in single-photon regime. In addition, the dimerization confers Rh an affinity for lipid raft, i.e. raftophilicity. However, the mechanism by which Rh-dimer raftophilicity contributes to the organization of the higher order structure remains unknown. In this study, we performed coarse-grained molecular dynamics simulations of a disk membrane model containing unsaturated lipids, saturated lipids with cholesterol, and Rh-dimers. We described the Rh-dimers by two-dimensional particle populations where the palmitoyl moieties of each Rh exhibits raftophilicity. We simulated the structuring of Rh in a disk for two types of Rh-dimer, i.e., the most and second most stable Rh dimers, which exposes the raftophilic regions at the dimerization-interface (H1/H8 dimer) and two edges away from the interface (H4/H5 dimer), respectively. Our simulations revealed that only the H1/H8 dimer could form a row structure. A small number of raftophilic lipids recruited to and intercalated in a narrow space between H1/H8 dimers stabilize the side-by-side interaction between dimers in a row. Our results implicate that the nano-sized lipid raft domains act as a "glue" to organize the long row structures of Rh-dimers.

biophysics↗