Microbial and synthetic DNA rich in CpG dinucleotides stimulates Toll-like receptor 9 (TLR9), whereas DNA lacking CpG either is inert or can inhibit TLR9 activation. The molecular mechanisms by which TLR9 becomes activated or is inhibited are not well understood. Here we show that TLR9 bound to stimulatory and inhibitory DNA; however, only stimulatory DNA led to substantial conformational changes in the TLR9 ectodomain. In the steady state, 'inactive' TLR9 homodimers formed in an inactivated conformation. Binding of DNA containing CpG, but not of DNA lacking CpG, to TLR9 dimers resulted in allosteric changes in the TLR9 cytoplasmic signaling domains. In endosomes, conformational changes induced by DNA containing CpG resulted in close apposition of the cytoplasmic signaling domains, a change that is probably required for the recruitment of signaling adaptor molecules. Our results indicate that the formation of TLR9 dimers is not sufficient for its activation but instead that TLR9 activation is regulated by conformational changes induced by DNA containing CpG.

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Riboflavin transporters (RFTs) and the riboflavin carrier protein (RCP) are highly upregulated in many tumor cells, tumor stem cells, and tumor neovasculature, which makes them attractive targets for nanomedicines. Addressing cells in different tumor compartments requires drug carriers, which are not only able to accumulate via the EPR effect but also to extravasate, target specific cell populations, and get internalized by cells. Reasoning that antibodies are among the most efficient targeting systems developed by nature, we consider their size (∼10-15 nm) to be ideal for balancing passive and active tumor targeting. Therefore, small, short-circulating (10 kDa, ∼7 nm, t ∼ 1 h) and larger, longer-circulating (40 kDa, ∼13 nm, t ∼ 13 h) riboflavin-targeted branched PEG polymers were synthesized, and their biodistribution and target site accumulation were evaluated in mice bearing angiogenic squamous cell carcinoma (A431) and desmoplastic prostate cancer (PC3) xenografts. The tumor accumulation of the 10 kDa PEG was characterized by rapid intercompartmental exchange and significantly improved upon active targeting with riboflavin (RF). The 40 kDa PEG accumulated in tumors four times more efficiently than the small polymer, but its accumulation did not profit from active RF-targeting. However, RF-targeting enhanced the cellular internalization in both tumor models and for both polymer sizes. Interestingly, the nanocarriers' cell-uptake in tumors was not directly correlated with the extent of accumulation. For example, in both tumor models the small RF-PEG accumulated much less strongly than the large passively targeted PEG but showed significantly higher intracellular amounts 24 h after iv administration. Additionally, the size of the polymer determined its preferential uptake by different tumor cell compartments: the 10 kDa RF-PEGs most efficiently targeted cancer cells, whereas the highest uptake of the 40 kDa RF-PEGs was observed in tumor-associated macrophages. These findings imply that drug carriers with sizes in the range of therapeutic antibodies show balanced properties with respect to passive accumulation, tissue penetration, and active targeting. Besides highlighting the potential of RF-mediated (cancer) cell targeting, we show that strong tumor accumulation does not automatically mean high cellular uptake and that the nanocarriers' size plays a critical role in cell- and compartment-specific drug targeting.

The main function of the transmembrane light-harvesting complexes in photosynthetic organisms is the absorption of a light quantum and its subsequent rapid transfer to a reaction center where a charge separation occurs. A combination of freeze-thaw and dialysis methods were used to reconstitute the detergent-solubilized Light Harvesting 2 complex (LH2) of the purple bacterium Rhodopseudomonas acidophila strain 10050 into preformed egg phosphatidylcholine liposomes, without the need for extra chemical agents. The LH2-containing liposomes opened up to a flat bilayer, which were imaged with tapping and contact mode atomic force microscopy under ambient and physiological conditions, respectively. The LH2 complexes were packed in quasicrystalline domains. The endoplasmic and periplasmic sides of the LH2 complexes could be distinguished by the difference in height of the protrusions from the lipid bilayer. The results indicate that the complexes entered in intact liposomes. In addition, it was observed that the most hydrophilic side, the periplasmic, enters first in the membrane. In contact mode the molecular structure of the periplasmic side of the transmembrane pigment-protein complex was observed. Using Föster's theory for describing the distance dependent energy transfer, we estimate the dipole strength for energy transfer between two neighboring LH2s, based on the architecture of the imaged unit cell.

The effect of confinement on dynamics and rheology of dilute deoxyribose nucleic acid solutions. II. Effective rheology and single chain dynamics