Namdoo Kim

Fluorescent indicators for simultaneous reporting of all four cell cycle phases

A robust method for simultaneous visualization of all four cell cycle phases in living cells is highly desirable. We developed an intensiometric reporter of the transition from S to G2 phase and engineered a far-red fluorescent protein, mMaroon1, to visualize chromatin condensation in mitosis. We combined these new reporters with the previously described Fucci system to create Fucci4, a set of four orthogonal fluorescent indicators that together resolve all cell cycle phases.

Rapid and facile synthesis of a (ZnxAgyInz)S2 nanocrystal library via sono-combichem method and its characterization including single nanocrystal analysis

We have developed a facile and rapid synthesis of a highly fluorescent nanocrystal (NC) library, based on ultrasonic and combinatorial chemistry. Among a total of 66 tZAIS ((ZnxAgyInz)S2) NCs, many NCs are highly fluorescent upon UV irradiation, and are categorized into blue, green, yellow, orange, and red by their distinct emission wavelength ranges. The tZAIS NCs not only have long fluorescence lifetimes, but also show comparable or even higher brightness than QDs without photoblinking in single NC analysis. Their unique photophysical properties together with less-toxic nature can permit the tZAIS system to be practically utilized in various bioimaging fields, especially single nanoparticle-based imaging and tracking.

Understanding CRY2 interactions for optical control of intracellular signaling

Arabidopsis cryptochrome 2 (CRY2) can simultaneously undergo light-dependent CRY2–CRY2 homo-oligomerization and CRY2–CIB1 hetero-dimerization, both of which have been widely used to optically control intracellular processes. Applications using CRY2–CIB1 interaction desire minimal CRY2 homo-oligomerization to avoid unintended complications, while those utilizing CRY2–CRY2 interaction prefer robust homo-oligomerization. However, selecting the type of CRY2 interaction has not been possible as the molecular mechanisms underlying CRY2 interactions are unknown. Here we report CRY2–CIB1 and CRY2–CRY2 interactions are governed by well-separated protein interfaces at the two termini of CRY2. N-terminal charges are critical for CRY2–CIB1 interaction. Moreover, two C-terminal charges impact CRY2 homo-oligomerization, with positive charges facilitating oligomerization and negative charges inhibiting it. By engineering C-terminal charges, we develop CRY2high and CRY2low with elevated or suppressed oligomerization respectively, which we use to tune the levels of Raf/MEK/ERK signaling. These results contribute to our understanding of the mechanisms underlying light-induced CRY2 interactions and enhance the controllability of CRY2-based optogenetic systems.Cryptochrome 2 (CRY2) can form light-regulated CRY2-CRY2 homo-oligomers or CRY2-CIB1 hetero-dimers, but modulating these interactions is difficult owing to the lack of interaction mechanism. Here the authors identify the interactions facilitating homo-oligomers and introduce mutations to create low and high oligomerization versions.

Electron affinity of phenanthrene and ion core structure of its anion clusters

We studied anion clusters of phenanthrene, Pnn− (n = 1–8), by mass distributions, photoelectron spectra, and theoretical calculations to determine the electron affinity of phenanthrene and the ion core structures of Pnn−. The electron affinity of phenanthrene was determined to be 0.12 eV. The parallel-displaced structures with a fully delocalized excess electron over the entire phenanthrene moieties, which were obtained as stable geometries in the theoretical calculations, implied the presence of dimeric and trimeric ion cores in Pn2− and Pn3−, respectively. For the tetramer and pentamer, photoelectron spectra with broad features and shoulders suggested the coexistence of ion cores. The magic number in the mass distributions and the unusual vertical detachment energy in the hexamer indicated the formation of a half-filled solvation shell.

Atomic selectivity in dissociative electron attachment to dihalobenzenes

We investigated electron attachment to three dihalobenzene molecules, bromochlorobenzene (BCB), bromoiodobenzene (BIB) and chloroiodobenzene (CIB), by molecular beam photoelectron spectroscopy. The most prominent product of electron attachment in the anion mass spectra was the atomic fragment of the less electronegative halogen of the two, i.e., Br(-) for BCB and I(-) for BIB and CIB. Photoelectron spectroscopy and ab initio calculations suggested that the approaching electron prefers to attack the less electronegative atom, a seemingly counterintuitive finding but consistent with the mass spectrometric result. For the iodine-containing species BIB and CIB, the photoelectron spectrum consists of bands from both the molecular anion and atomic I(-), the latter of which is produced by photodissociation of the former. Molecular orbital analysis revealed that a large degree of orbital energy reordering takes place upon electron attachment. These phenomena were shown to be readily explained by simple molecular orbital theory and the electronegativity of the halogen atoms.