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Crystal phase and morphology of biominerals may be precisely regulated by controlled nucleation and selective crystal growth through biomineralization on organic templates such as a protein. We herein propose new control factors of selective crystal growth by the biomineralization process. In this study, a designed β-sheet Ac-VHVEVS-CONH2 peptide was used as a multifunctional template that acted as mineral source supplier and having crystal phase control ability of calcium carbonate (CaCO3) during a self-supplied mineralization. The peptides formed three-dimensional nanofiber networks composed of assembled bilayer β-sheets. The assembly hydrolyzed urea molecules to one carbonate anion and two ammonium cations owing to a charge relay effect between His and Ser residues under mild conditions. CaCO3 was selectively mineralized on the peptide assembly using the generated carbonate anions on the template. Morphology of the obtained CaCO3 was fiber-like structure, similar to that of the peptide template. The mineralized CaCO3 on the peptide template had aragonite phase. This implies that CaCO3 nuclei, generated using the carbonate anions produced by the hydrolysis of urea on the surface of the peptide assembly, preferentially grew into aragonite phase, the growth axis of which aligned parallel to the direction of the β-sheet fiber axis.

We studied the effect of surface-functional-group position on precipitate morphology in the earliest stage of calcium phosphate biomineralization and determined the detailed mechanism of precipitation starting from nucleation to precipitate growth. The biomineralization template was a β-sheet peptide scaffold prepared by adsorption with carboxyl groups arranged at strict 7 Å intervals. Phosphate was then introduced. Within 10 s, highly ordered embryos of calcium phosphate were formed and confined by a peptide nanofiber pattern. They repeatedly nucleated and dissolved, with the larger embryos absorbing the smaller ones in a clear demonstration of an Ostwald-ripening-like phenomenon, then aggregated in a line pattern, and finally formed highly ordered nanofibers of amorphous calcium phosphate. This multistep growth process constitutes the earliest stage of biomineralization.

Gold nanoparticles having sequential alternating amphiphilic peptide chains, Phe-(Leu-Glu)8, on the surface have been prepared. We describe structural control of the amphiphilic peptide coated gold nanoparticle assembly by a conformational transition of the surface peptides. Under the acidic condition, the conformation of the surface amphiphilic peptide was converted to a beta-sheet structure from an aggregated alpha-helix by incubation. Under this condition, the amphiphilic peptide coated gold nanoparticles formed a nanosheet assembly. The plasmon absorption maximum of the gold nanoparticles shifted to a shorter wavelength with the formation of the beta-sheet assembly of the surface peptide. This suggests that the structure of the peptide coated gold nanoparticle assembly could be controlled by the conformational transition of the surface peptide. Furthermore, the core gold nanoparticle could be fixed in the beta-sheet assembly in the state that stood alone. This system may be useful for novel molecular devices that exhibit quantized properties.

One of the essential parts in the molecular mechanism of biological properties is the structural changes of proteins induced by stimuli. An amphiphilic copolymer, poly(L-leucine) grafted polyallylamine as a simple model of proteins, has been prepared by NCA polymerization with free amino groups of polyallylamine as an initiator. Here, we report the pH-induced reversible conformational and morphological regulation of the amphiphilic copolymer, whose hydrophobic peptide graft chains have no pH-sensitive groups, in an aqueous solution containing 50 vol % trifluoroethanol. The conformation of the poly(L-leucine) graft chain was found to be strongly pH dependent. Under acidic conditions, where electrostatic repulsion existed between the neighboring protonated amine moieties of the polyallylamine main chain, the rapid aggregation of the poly(l-leucine) graft chains was disturbed, and the peptide graft chains formed a beta-sheet structure owing to the intramolecular hydrogen bonding among the graft chains. Under this condition, the amphiphilic polymer formed amyloid-like fibrils, and then the fibrils grew into a planer plate composed of staked beta-sheets. On the other hand, under basic conditions, the poly(L-leucine) graft chains showed conformational transitions from a beta-sheet structure to an alpha-helical conformation owing to a distortion of the regular arrangement of the peptide graft chains by the conformational change of the polyallylamine main chain, whose amino groups were deprotonated. The conformational transition resulted in a disturbance of the regular sheet assembly of the amphiphilic copolymer and induced morphological changes to the amorphous globular aggregates. The pH-induced conformational and morphological changes of the poly(L-leucine) graft polyallylamine were reversible and synchronized with the protonation of the polyallylamine main chain.

Poly(γ-methyl l-glutamate)s with Asp, Tyr, Trp, and Ser residues at the amino terminal as the binding sites in the nicotinic acetylcoline receptor and γ-aminobutyric acid receptor, respectively, we...

An amphiphilic polymer, poly(allylamine) (Mw = 10 000) containing 37 mol % poly(l-alanine) hydrophobic graft chains (PAAgPAla), was prepared. The average degree of polymerization of the poly(l-alanine) graft chains was determined to be 13. The amphiphilic polymer was observed to form a monolayer at the air−water interface. We investigated the structure and molecular recognition properties of the monolayer using π−A isotherm measurement, reflection−absorption Fourier transform infrared spectroscopy, fluorescence anisotropy, atomic force microscopy, and surface plasmon resonance. The structure of the monolayer was found to be strongly pH dependent in an aqueous solution. In acidic conditions, the protonated allylamine moieties of PAAgPAla dissolved readily into the aqueous phase, while the hydrophobic poly(l-alanine) graft chains acted as anchors to keep the monolayer at the interface, resulting in the formation of a collapsed monolayer. In alkaline conditions, the PAAgPAla chains were located entirely at t...

We prepared a photoresponsive polypeptide, M n = 10 630, composed of two amphiphilic α-helical copolypeptides, poly[(γ-methyl L-glutamate)-co-(L-glutamic acid)], joined by an azobenzene (am.-MAzoM) as a molecular photoreceptor. Dipalmitoylphosphatidylcholine monolayers containing the am.-MAzoM were formed at the air-water interface. We investigated photoinduced changes in the structure of the polypeptide-lipid monolayer systems. The α-helical rod of am.-MAzoM was laid at the air-water interface when the monolayer was in a liquid state. While in the solid condensed monolayer, the polypeptide molecules arranged perpendicular to the membrane (the air-water interface) and formed a bundle by self-association. The bundle of am.-MAzoM could be observed as an intramembranous particle ca. 4 nm in diameter with atomic force microscopy. UV light irradiation induced the destabilization of the bundle structure in the monolayer. This behavior arose from the photoinduced denaturation of the amphiphilic character of the polypeptide owing to a bending of the polypeptide in the main chain by a cis-trans photoisomerization of the azobenzene moiety. After removal of the light, the am.-MAzoM in the solid condensed monolayer returned to the original bundle structure.