Takatoshi Kinoshita

Polypeptide membranes at an interface

Abstract A main focus of this review is to examine the possibility of controlling the surface and interface structure at the nanometer-scale, i.e. self-organized nanostructures, such as size, shape, density and orientation using mainly rod-like α-helical polypeptides. The molecular arrangement of these polypeptides, such as normal and/or parallel orientation of the helix to the membrane face, side-by-side helix self-assembling monolayer and well-defined nanometer-layered structure on the substrate, is directly reflected in the functions of the molecular membrane systems. For example, the guest-induced oscillatory membranes, nanopatterned monolayer structure and structural color formation of Langmuir–Blodgett films will be introduced as a recent topic on the structure–function relationships of polypeptide molecular membranes at various interfaces.

Biomembrane mimetic systems

Abstract Based on the determination of the biological design of membrane protein two approaches for mimicking the intelligent function of biological members are proposed: (1) molecular design of structural module of membrane proteins and the functional analysis of the designed elements incorporated in membrane systems; (2) functional modeling of biological membranes such as stimulus-response coupling, information transfer, energy transformation, membrane recognition, and so on. This review will summarize recent developments in biomembrane mimetic systems based on this fundamental concept for mimicking the biological membranes. Model systems concerning ion channels and chemo- and photosensory systems in biological membranes will be discussed in some detail.

Studies on visual sensor from self-assembled polypeptides

Abstract A silane terminated poly (ε-benzyloxycarbonyl-L-lysine) was synthesized and deposited as a self-assembled monolayer on the pre-colored silica substrate which was fabricated by Langmuir–Blodgett (LB) method. The monolayer was covalently attached to silica surface through terminal silane groups. The secondary structure of polymer, α-helix, was confirmed by circular dichroism spectroscopy. Furthermore, the conversion of the monolayer surface from non-ionic to cationic was accomplished by removal of ε-benzyloxycarbonyl group (Z group). The uniform monolayer on silica substrate and the changes occurring in the tethered monolayer were analyzed by atomic force microscopy (AFM). RNA aptamer with 72 sequences of nucleotides could be immobilized on the poly (L-lysine) cationic surface through electrostatic interaction. The superior recognition capability of RNA aptamer with specific microorganism is becoming a promising candidate in detection of bacteria. In this study, the binding of target bacteria, Sphingobium yanoikuyae, to the resulting RNA probe leads to a color change at the surface which is visually observed by real-time and confirmed through UV-reflective spectrophotometer. The RNA probes can be used as a high efficiency and versatile tool to visually sense the bacterial contamination in the food products.

Construction of Polypeptide-based Nano-template

Self-organization of the ordered nano-structures composed of amphiphilic polypeptides is focused in this review. Two-dimensional arrangement of rod-like block type copolypeptides at interface has been investigated by Langmuir–Blodgett (LB) method. A diblock helical copolypeptide formed stripe pattern in the LB film based on nano-phase separation. In the case of triblock helical copolypeptide, more sophisticated nano-stripe pattern was produced. The triblock copolypeptide LB film was applied as a nano-template, i.e., iron nano-particles fabricated their joined nano-wire reflecting the lane-like pattern in the LB film.LB films of monodispersed triblock copolypeptides having leucine zipper helices at the termini (helix–loop–helix type) with designed sequence indicated not only a sophisticated nano-stripe pattern over a wide range but also a quantitative increase in the stripe interval depending on the size of loop segment. It was also shown that the mixed LB film consisting of the helix–loop–helix copolypeptide and leucine zipper helical polypeptide provided a unique phase separated structure, having a uniform rectangular-like domain. Furthermore, it was reported that the monodispersed amphiphilic β-sheet peptide formed three-dimensionally self-organized nano-fiber scaffold, yielding a transparent hydrogel containing extremely higher water content (>99.5%).The well-defined amphiphilic polypeptides with designed sequence and conformation emerging into various intra- and inter-molecular interactions into self-assembled nano-organization will likely have great impact on the future of materials. These hierarchical ordering structures including location and arrangement of functional units on nanometer-scale will be developed for a wide range of application as a nano-template.

pH-Regulated formation of amyloid-like β-sheet assemblies from polyglutamate grafted polyallylamine

A novel artificial protein with simple primary structure, poly(gamma-methyl-L-glutamate)-grafted polyallylamine, has been prepared and the resultant peptide has shown a unique property of pH-regulated conformation and morphology.

Fabrication of vertically and unidirectionally oriented polypeptide assemblies on self-assembled monolayers by stepwise polymerization

A polypeptide assembly prepared by stepwise polymerization on a self-assembled monolayer consisting of amino-alkanethiol and dialkyl disulfide oriented vertically and unidirectionally to the surface.