Nam Ki Lee

Ab initio calculations were carried out for the naphthalene dimer and naphthalene–anthracene complex to determine their stable geometries and binding energies. Two medium-size basis sets of 6-31G*(0.25) and 6-31+G* were employed at the MP2 level. Five local minima were found for the naphthalene dimer, three of which were parallel-displaced type and the other two T-shaped type. The global minimum geometry was a parallel-displaced structure of a two-layer graphitic type (Ci point group), not the c

Single-molecule fluorescence resonance energy transfer (smFRET) is one of the powerful techniques for deciphering the dynamics of unsynchronized biomolecules. However, smFRET is limited in its temporal resolution for observing dynamics. Here, we report a novel method for observing real-time dynamics with submillisecond resolution by tethering molecules to freely diffusing 100-nm-sized liposomes. The observation time for a diffusing molecule is extended to 100 ms with a submillisecond resolution,

The folding of 8-17 deoxyribozyme was investigated by three-color alternating-laser excitation (3c-ALEX), a new single-molecule fluorescence resonance energy transfer (FRET) method we recently developed. Since 3c-ALEX has the capability of simultaneously sorting fluorescent molecules based on their labeling status and monitoring three interprobe distances of a biomolecule by employing three-color FRET, it is an ideal tool to study folding of multibranched molecules. The 8-17 deoxyribozyme, a DNA

Molecular emitters simultaneously generating light at different wavelengths have wide applications. With a small molecule, however, it is challenging to realize two independent radiative pathways. We invented the first examples of dual-emissive single-benzene fluorophores (SBFs). Two emissive tautomers are generated by synthetic modulation of the hydrogen bond acidity, which opens up pathways for excited-state proton transfer. White light is produced by a delicate balance between the energy and

Z-DNA, a noncanonical helical structure of double-stranded DNA (dsDNA), plays pivotal roles in various biological processes, including transcription regulation. Mechanical stresses on dsDNA, such as twisting and stretching, help to form Z-DNA. However, the effect of DNA bending, one of the most common dsDNA deformations, on Z-DNA formation is utterly unknown. Here, we show that DNA bending induces the formation of Z-DNA, that is, more Z-DNA is formed as the bending force becomes stronger. We reg

The stable geometries and binding energies of the benzene–naphthalene complex were studied by the point-by-point method using ab initio calculations at the MP2/6-31G*(0.25) and MP2/6-31+G* levels. Medium-size basis sets were employed not only to save computational time but also to compensate for the tendency of the MP2 method to overestimate the electron correlation energy of aromatic clusters. The use of the 6-31G*(0.25) and 6-31+G* basis sets in the test calculation for the benzene dimer yield

Neuronal communication depends on exquisitely regulated membrane fusion between synaptic vesicles and presynaptic neurons, which results in neurotransmitter release in precisely timed patterns. Presynaptic dysfunctions are known to occur prior to the onset of neurodegenerative diseases, including Parkinson's disease. Synaptic accumulation of α-synuclein (α-Syn) oligomers has been implicated in the pathway leading to such outcomes. α-Syn oligomers exert aberrant effects on presynaptic fusion mach

Cellular processes occur through the orchestration of multi-step molecular reactions. Reaction progress kinetic analysis (RPKA) can provide the mechanistic details to elucidate the multi-step molecular reactions. However, current tools have limited ability to simultaneously monitor dynamic variations in multiple complex states at the single molecule level to apply RPKA in living cells. In this research, a single particle tracking-based reaction progress kinetic analysis (sptRPKA) was developed t

Interactions between membrane proteins are poorly understood despite their importance in cell signaling and drug development. Here, we present a co-immunoimmobilization assay (Co-II) enabling the direct observation of membrane protein interactions in single living cells that overcomes the limitations of currently prevalent proximity-based indirect methods. Using Co-II, we investigated the transient homodimerizations of epidermal growth factor receptor (EGFR) and beta-2 adrenergic receptor (β2-AR

We present a single-molecule diffusional-mobility-shift assay (smDIMSA) for analyzing the interactions between membrane and water-soluble proteins in the crowded membrane of living cells. We found that ligand-receptor interactions decreased the diffusional mobility of ErbB receptors and β-adrenergic receptors, as determined by single-particle tracking with super-resolution microscopy. The shift in diffusional mobility was sensitive to the size of the water-soluble binders that ranged from a few

Using a single-molecule fluorescence method uniquely suitable for binding assay, alternating-laser excitation fluorescence resonance energy transfer (ALEX-FRET), we accurately measured the cleavage rate of 8-17 deoxyribozyme, an RNA-cleaving enzyme, at the single-molecule level in real time with a minimum consumption of samples, i.e., at least three orders of magnitude smaller than used in the conventional ensemble FRET method.

Bending with high curvature is one of the major mechanical properties of double-stranded DNA (dsDNA) that is essential for its biological functions. The emergence of a kink arising from local melting in the middle of dsDNA has been suggested as a mechanism of releasing the energy cost of bending. Herein, we report that strong bending induces two types of short dsDNA deformations, induced by two types of local melting, namely, a kink in the middle and forks at the ends, which we demonstrate using

Using a single-molecule method, we directly distinguish among oligomers from monomers to tetramers and determine their quaternary structures. Using this method, we found that RecR forms a stable dimer and its oligomeric form is modulated by its own concentration and the interaction with RecO.