I am personally interested in molecular mechanisms, how education and other experiences during human development influence cognitive ability and personality in the adult. For understanding brain and other biological functions from molecular level, structure analyses of membrane proteins are important and electron microscopy is a good candidate for structure analyses of membrane proteins. Radiation damage of biological material is however extremely serious. We therefore developed a helium cooled cryo–EM. Based on electron crystallography utilizing the cryo–EM, for example, we could discriminate 8 water molecules in water channel AQP4, while their densities were blurred in the higher resolution structure by X–ray crystallography. The counterintuitive notion could be attributed to the difference of surround atmosphere for structure analyses of membrane proteins. The characteristic distribution of the dielectric constants in membrane produces large dipole moment of the two short helices of water channel, whereas the dipole moment without lipid bilayer is very small. In cooperation with the electrostatic field of two short helices, the arrangement of carbonyl groups in the channel acts as binding sited in the narrow channel with highly hydrophobic surfaces and lowers the energy barrier for water molecules entering narrow water channel. The water stable positions guided by the polypeptide carbonyl and amide groups of highly conserved NPA motifs may make 3 billion water molecules pass through the channel in a second. The results strongly suggest that electron crystallography is very powerful method for understanding physiological functions of membrane proteins. The necessity of crystallization, however, makes this method less popular in structural biology. Now, many structures have been analyzed by single particle analysis. Actually, we could analyze structure of gap junction channel of invertebrate in very short period, while we could analyze no high resolution structure of it by crystallography. The good quality map at 3.3 Å resolution by cryo–EM single particle analysis enables us to make de novo chain tracing. Very effective and fast structure analysis of membrane protein may facilitate to develop a new strategy named drug rescuing.

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Mammalian cells are known to communicate with distant cells through extracellar vesicles such as exosomes and microvesicles. While microvesicles are formed by shedding of plasma membranes, exosomes are generated by the fusion of multivesicular endosomes (MVEs) with plasma membranes and release their internal intralumenal vesicles (ILVs) as exosomes. Recently, exosome research attracts great attention since exosomes play important roles in antigen presentation, propagation of cancer malignancy, and spread of neurodegenerative diseases. This review will present recent knowledge of the mechanism underlying exosome biogenesis based on sphingolipid metabolites including ceramide and sphingosine 1–phosphate (S1P). Current topics on neurodegenerative disorders such as alpha-synucleopathy in terms of insufficiency of S1P signaling is also briefly introduced.

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Lipid bilayer of bacterial cell membrane is mainly composed of phospholipids with various head groups and fatty acyl groups. These phospholipids are synthesized from phosphatidic acid via CDP–diacylglycerol in the de novo pathway. In the biosynthesis of phosphatidic acid, two acyl groups at the sn–1 and sn–2 positions are introduced sequentially in this order by the action of PlsB (or PlsX/PlsY) and PlsC, respectively. Recently, new types of PlsCs, which introduce polyunsaturated fatty acyl groups and branched–chain fatty acyl groups into phospholipids, were discovered from a marine bacterium, Shewanella livingstonensis Ac10. Occurrence of a great diversity of phospholipids in bacterial cell membrane suggests that individual phospholipids have their own specific physiological function. Indeed, eicosapentaenoic acid–containing phospholipids, for example, were shown to be involved in cell division and membrane protein biogenesis in S. livingstonensis Ac10. Recent topics in the field of bacterial membrane phospholipid research, in particular those from our group, are described in this review.

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Autophagy is an intracellular degradation pathway, in which degradation targets are sequestered by a double membrane vesicle called the autophagosome, transported to, and degraded in the lysosome or vacuole. Recent studies revealed that some organelles, such as mitochondria and peroxisomes, are marked by “autophagy receptors”, and selectively engulfed by the autophagosome. Here, I describe our recent discovery of selective autophagy of the endoplasmic reticulum and nucleus in the budding yeast Saccharomyces cerevisiae.

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The recent status of studies on temperature–sensitive water-soluble polymers is briefly reviewed. The concept of cooperative dehydration, defined as simultaneous dissociation of the water molecules bound to a polymer chain in correlated sequences, has been applied to study the collapse transition and LCST phase separation of temperaturesensitive polymer, poly(N–isopropylacrylamide), in water and in mixed solvents of water and methanol. The transition becomes sharper as the cooperativity of (de)hydration increases. The sharp depression by the LCST co–nonsolvency in the mixed solvents is shown to be caused by the competitive hydrogen bonding of water and methanol seeking for hydrogen–bonding sites on the polymer chains. The degree of hydration and of methanol binding, preferential adsorption coefficients, LCST cloud–point depression are theoretically calculated and compared with the experiments. The shifts of LCST induced by added salts (salting–in and salting-out effect) are briefly discussed from the viewpoint of competing polymer hydration and ionic hydration, with focus on anion binding.

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In living systems, there are many autonomous and oscillatory phenomena to sustain life such as heart beating. We developed “self–oscillating” polymer gels that undergo spontaneous cyclic swelling–deswelling changes without any on–off switching of external stimuli, as with heart muscle. The self–oscillating gels were designed by utilizing the Belousov–Zhabotinsky (BZ) reaction, an oscillating reaction, as a chemical model of the TCA cycle. We have systematically studied these self–oscillating polymer gels since they were first reported in 1996. In this review, our recent progress on the self–oscillating polymer gels is summarized.

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We have recently developed a novel type of polymer network called slide–ring materials by cross–linking polyrotaxane, the supramolecular architecture with topological characteristics. In the network, polymer chains are topologically interlocked by figure–of–eight cross–links. Hence, these cross–links can pass along the polymer chains freely to equalize the tension of the threading polymer chains similarly to pulleys. The structure and physical properties of the polymeric materials are drastically different from conventional cross–linked or noncross–linked materials. For instance, the slide–ring gel membrane shows nonlinear penetration flow properties. The concept of the slide-ring materials is not limited to cross–linked gels but includes elastomer, cross-linked polymeric materials without solvent.

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Lipid nanodiscs are discoidal particles with a planar phospholipid bilayer enwrapped by polypeptide chains such as apolipoprotein A–I, membrane scaffold protein (MSP), and amphiphilic class A α– helical peptides. Nanodiscs have been widely used for analyzing structures and functions of membrane proteins by dispersing them in solution. They are expected to be used as drug carriers and therapeutic agents. This review focuses on the nanodisc-forming amphiphilic peptides. An amphiphilic self–polymerizing peptide termed ASPP1, which polymerizes by intermolecular native chemical ligation, was synthesized. ASPP1 spontaneously formed nanodiscs when added to phospholipid vesicles without using detergents. The diameter of the planar lipid bilayer in the nanodiscs was controlled within a range of 15 to 30 nm by the lipid : peptide molar ratio. ASPP1–nanodiscs exhibited greater stability at high temperatures or in the presence of urea than nanodiscs formed by the non–polymerizing amphiphilic peptide or apolipoprotein A–I. These results show that the lipid–peptide nanodiscs provide promise for future applications.

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Arginine–rich peptides directly penetrate into cells across cell membranes via spontaneous energy–independent process. We demonstrated that interaction of arginine–rich peptides with sulfated glycosaminoglycans (GAGs) at the cell surface plays a critical role in their cell membrane penetrations: the high–affinity binding of arginine–rich peptides to GAGs is driven by favorable enthalpy contributions, resulting in the efficient cell membrane penetration. The enthalpy gain is possibly derived from a unique property of the guanidino group in arginine to form multidentate hydrogen bonding with sulfate and carboxylate groups of GAGs. Such GAG interaction can be accompanied with charge neutralization of arginine–rich peptides, promoting their cell membrane penetration. Taken together with our finding that arginine–rich peptides cross the lipid membranes through membrane perturbation, a mechanism for the cell membrane penetration has been proposed: the mechanism involves (1) binding to GAG at the cell surface, followed by (2) the transfer to the cell membrane and (3) the entry into cytosol.

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We conducted exploratory research of high–efficient membrane processes for gas separation using a sweep counter flow module (SCM). Calculated results for biogas upgrading example were compared by using economic efficiency indexes. When a sweep ratio (SR) is less than 0.1, SCM can be designed resulting to keep the same level of power requirement and reduce the membrane area than that of normal counter flow module (NCM). A recovery of methane, however, can’t exceed over that of NCM. To improve the recovery without losing economical advantage of NCM two stage series (TSS) processes were newly designed by employing a SCM as the first stage (TSFSC) or the second stage (TSSSC). These two processes can yield higher recovery as increasing recycle ratios (RR) of permeates from the second to feeds of the first. Especially, TSSSC designed by SR＝ 0.1 and RR＝ 0.7 ～ 1 using a membrane of α＊≧ 30 is significantly efficient and economical, in which methane recovery is more than 0.9 and membrane area requirement is less than that of NCM keeping the same level of specific power requirement.

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