Transmission of extramembrane conformational change into current: construction of metal-gated ion channel

Interaction with Fe(III) induces the reversible conformational switch of the extramembrane segment in the artificial receptor channel, which is transmitted into membranes as an increase in channel current (ion flux).     

Surface phase behavior of di-n-tetradecyl hydrogen phosphate in Langmuir monolayers at the air-water interface

Surface phase behavior of di-n-tetradecyl hydrogen phosphate, DTP, has been studied by measuring pi-A isotherms with a film balance and observing monolayer morphology with a Brewster angle microscopy (BAM) at different temperatures. A generalized phase diagram, which shows a triple point for gas (G), liquid-expanded (LE) and liquid-condensed (LC) phases at about 32 degrees C, is constructed for the amphiphile. Below the triple point, a first-order G-LC phase transition has been shown to occur, whereas a first-order G-LE phase transition followed by another first-order LE-LC transition has been found to take place at a temperature above the triple point. The amphiphile shows the fingering LC domains with uniform brightness indicating the presence of untilted molecules. The domain shapes are independent of the change in temperature and compression rate. The existence of similar fingering domains over a wide range of temperature is rather uncommon in the monolayer systems and is considered to be due to the restricted movement of the molecules incorporating into the LC phase. Because the two-alkyl chains are directly attached to two covalent bonds of the phosphate head group, the rearrangement of the molecules, which is an essential condition for the circular domain formation, needs the movement of the whole molecules including the hydration sphere. The difficulty related to such a movement of the molecules causes fingering domains, which are independent of external variables.     

Lateral organization of a membrane protein in a supported binary lipid domain: direct observation of the organization of bacterial light-harvesting complex 2 by total internal reflection fluorescence microscopy

A unique method is described for directly observing the lateral organization of a membrane protein (bacterial light-harvesting complex LH2) in a supported lipid bilayer using total internal reflection fluorescence (TIRF) microscopy. The supported lipid bilayer consisted of anionic 1,2-dioleoyl-sn-glycero-3-[phospho-rac-(1'-glycerol)] (DOPG) and 1,2-distearoly-sn-3-[phospho-rac-(1'-glycerol)] (DSPG) and was formed through the rupture of a giant vesicle on a positively charged coverslip. TIRF microscopy revealed that the bilayer was composed of phase-separated domains. When a suspension of cationic phospholipid (1,2-dioleoyl-sn-glycero-3-ethylphosphocholine: EDOPC) vesicles (approximately 400 nm in diameter), containing LH2 complexes (EDOPC/LH2 = 1000/1), was put into contact with the supported lipid bilayer, the cationic vesicles immediately began to fuse and did so specifically with the fluid phase (DOPG-rich domain) of the supported bilayer. Fluorescence from the incorporated LH2 complexes gradually (over approximately 20 min) spread from the domain boundary into the gel domain (DSPG-rich domain). Similar diffusion into the domain-structured supported lipid membrane was observed when the fluorescent lipid (1,2-dioleoyl-sn-glycero-3-phosphoethanolamine-N-lissamine-rhodamine B sulfonyl: N-Rh-DOPE) was incorporated into the vesicles instead of LH2. These results indicate that vesicles containing LH2 and lipids preferentially fuse with the fluid domain, after which they laterally diffuse into the gel domain. This report describes for first time the lateral organization of a membrane protein, LH2, via vesicle fusion and subsequent lateral diffusion of the LH2 from the fluid to the gel domains in the supported lipid bilayer. The biological implications and applications of the present study are briefly discussed.     

Synthesis and ring size effect of macrocyclic ethynylhelicene oligomers

[reaction: see text] The cyclization of acyclic ethynylhelicene oligomers with decyl 3,5-diiodobenzoate under optimized conditions gave the corresponding optically active [n+n]cycloalkynes (n = 4-8) in high yields. Their structures were compared in terms of ring size by using (1)H NMR, UV-vis, and CD spectroscopies and vapor pressure osmometry (VPO). The UV-vis spectra exhibited an increase in absorbance in proportion to n. In contrast, the CD spectra of the macrocycles exhibited a large ring size effect, comparable Deltaepsilon values despite the increase in n and temperature-dependent properties of the [8+8]cycloalkyne. It was concluded that [4+4]cycloalkyne, [5+5]cycloalkyne, [6+6]cycloalkyne, and [7+7]cycloalkyne have rigid structures, while [8+8]cycloalkyne has a flexible structure.     

Synthesis of a 1α-C-methyl analogue of 25-hydroxyvitamin D3: interaction with a mutant vitamin D receptor Arg274Leu

Vitamin D₃ analogues have been developed for a mutant vitamin D receptor (VDR), Arg274Leu. The mutant VDR has a mutation at Arg274, which forms an important hydrogen bond with 1α-OH of 1α,25-dihydroxyvitamin D₃ to anchor the ligand tightly in the VDR ligand binding pocket. Stereoselective synthesis of the A-ring part of the novel vitamin D analogue, 2α-(3-hydroxypropyl)-1α-methyl-25-hydroxyvitamin D₃ (4), from d-galactose was accomplished with the key steps of the introduction of the methyl and allyl groups to the chiral building blocks. The new analogue 4 is ca. 7.3-fold more active than the natural hormone 1α,25-dihydroxyvitamin D₃ (1).