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KillerRed is the only known fluorescent protein that demonstrates notable phototoxicity, exceeding that of the other green and red fluorescent proteins by at least 1,000-fold. KillerRed could serve as an instrument to inactivate target proteins or to kill cell populations in photodynamic therapy. However, the nature of KillerRed phototoxicity has remained unclear, impeding the development of more phototoxic variants. Here we present the results of a high resolution crystallographic study of KillerRed in the active fluorescent and in the photobleached non-fluorescent states. A unique and striking feature of the structure is a waterfilled channel reaching the chromophore area from the end cap of the ␤-barrel that is probably one of the key structural features responsible for phototoxicity. A study of the structure-function relationship of KillerRed, supported by structure-based, site-directed mutagenesis, has also revealed the key residues most likely responsible for the phototoxic effect. In particular, Glu 68 and Ser 119, located adjacent to the chromophore, have been assigned as the primary trigger of the reaction chain. The green fluorescent protein (GFP)2 and related proteins have become efficient noninvasive tools in cell biology and biomedicine for visualizing and monitoring the internal processes within cells or whole organisms (1-8). The multicolor labeling technologies, based on fluorescent proteins (FPs), have found important biomedical applications in the studies of various aspects of cancer, including primary tumor growth, tumor cell motility and invasion, metastatic seeding, colonization, and angiogenesis (9 -11).The recent development of the first genetically encoded photosensitizer, KillerRed (SWISS-PROT/TrEMBL data base sequence ID Q2TCH5), a highly phototoxic red fluorescent protein (12, 13), opened a new area of FP application. KillerRed is a red fluorescent protein characterized by excitation and emission maxima at 585 and 610 nm, respectively. This genetic variant was engineered from non-fluorescent and non-phototoxic chromoprotein anm2CP from Hydrozoa jellyfish (sequence ID Q6RYS4). Upon irradiation by green light at the wavelength of 520 -590 nm, KillerRed generates the reactive oxygen species (ROS), accompanied by profound self photobleaching. The ROS-induced phototoxicity of KillerRed is at least 3 orders of magnitude higher than that of other fluorescent proteins exhibiting low background phototoxicity (12). Such a unique property of KillerRed could find use in light-induced inactivation of target proteins and in precise cell killing. Unlike chemical photosensitizers, KillerRed can be directly expressed by a target cell, both individually and in fusion with a target protein. The most exciting future application of KillerRed may be in photodynamic therapy of cancer. This phototoxic agent, precisely delivered to solid tumors by a viral vector, could serve as an intrinsically generated photosensitizer, causing light-induced tumor destruction. Therefore, understanding the relationship between...

Memristors are widely considered as promising elements for the efficient implementation of synaptic weights in artificial neural networks (ANNs) since they are resistors that keep memory of their previous conductive state. Whereas demonstrations of simple neural networks (e.g., a single-layer perceptron) based on memristors already exist, the implementation of more complicated networks is more challenging and has yet to be reported. In this study, we demonstrate linearly nonseparable combinational logic classification (XOR logic task) using a network implemented with CMOS-based neurons and organic memrisitive devices that constitutes the first step toward the realization of a double layer perceptron. We also show numerically the ability of such network to solve a principally analogue task which cannot be realized by digital devices. The obtained results prove the possibility to create a multilayer ANN based on memristive devices that paves the way for designing a more complex network such as the double layer perceptron.

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Polyaniline (PANI) based memristive devices have emerged as promising candidates for hardware implementation of artificial synapses (the key components of neuromorphic systems) due to their high flexibility, low cost, solution processability, three-dimensional stacking capability, and biocompatibility. Here, we report on a way of the significant improvement of the switching rate and endurance of PANI-based memristive devices. The reduction of the PANI active channel dimension leads to the increase in the resistive switching rate by hundreds of times in comparison with the conventional one. The miniaturized memristive device was shown to be stable within at least 104 cyclic switching events between high- and low-conductive states with a retention time of at least 103 s. The obtained results make PANI-based memristive devices potentially widely applicable in neuromorphic systems.

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From the base structure of tetragonal lysozyme crystals, the octamer cluster was selected as the possible element of crystal growth. The proposed model was verified by small-angle X-ray scattering (SAXS) measurements of lysozyme solutions. The results showed a noticeable presence of lysozyme dimers and octamers under crystallization conditions and the total absence of oligomers under conditions where crystal growth was impossible.