Efficiencies of the incorporation of various nonnatural amino acids carrying aromatic side groups into streptavidin were examined. The aromatic amino acids were linked to a mixed dinucleotide, pdCpA, and the resulting aminoacyl pdCpAs were coupled with tRNAcccg(−CA) to afford chemically aminoacylated tRNAcccg's. Mutant streptavidin mRNA containing a CGGG 4 base codon at the Tyr83 site was prepared and added to an Escherichia coli in vitro translation system with the aminoacyl tRNAcccg. The expression of the full-length mutant streptavidins was confirmed by a Western blot analysis, and their biotin binding activity was examined by a dot blot analysis. The Western blot analysis indicated that the efficiencies of the incorporation were higher for aromatic groups with straight configurations than those with widely expanded or bend configurations. The incorporation efficiencies were also examined in a rabbit reticulocyte lysate. In the latter system, the efficiencies were markedly improved for nonnatural amino acids with large side groups such as pyrene and anthraquinone.

We designed and synthesized new, fluorescent, non-natural amino acids that emit fluorescence of wavelengths longer than 500 nm and are accepted by an Escherichia coli cell-free translation system. We synthesized p-aminophenylalanine derivatives linked with BODIPY fluorophores at the p-amino group and introduced them into streptavidin using the four-base codon CGGG in a cell-free translation system. Practically, the incorporation efficiency was high enough for BODIPYFL, BODIPY558 and BODIPY576. Next, we incorporated BODIPYFL-aminophenylalanine and BODIPY558-aminophenylalanine into different positions of calmodulin as a donor and acceptor pair for fluorescence resonance energy transfer (FRET) using two four-base codons. Fluorescence spectra and polarization measurements revealed that substantial FRET changes upon the binding of calmodulin-binding peptide occurred for the double-labeled calmodulins containing BODIPY558 at the N terminus and BODIPYFL at the Gly40, Phe99 and Leu112 positions. These results demonstrate the usefulness of FRET based on the position-specific double incorporation of fluorescent amino acids for analyzing conformational changes of proteins.

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In this review, we introduce two kinds of bio-related nanoarchitectonics, DNA nanoarchitectonics and cellmacromolecular nanoarchitectonics, both of which are basically controlled by chemical strategies. The former DNA-based approach would represent the precise nature of the nanoarchitectonics based on the strict or "digital" molecular recognition between nucleic bases. This part includes functionalization of single DNAs by chemical means, modification of the main-chain or side-chain bases to achieve stronger DNA binding, DNA aptamers and DNAzymes. It also includes programmable assemblies of DNAs (DNA Origami) and their applications for delivery of drugs to target sites in vivo, sensing in vivo, and selective labeling of biomaterials in cells and in animals. In contrast to the digital molecular recognition between nucleic bases, cell membrane assemblies and their interaction with macromolecules are achieved through rather generic and "analog" interactions such as hydrophobic effects and electrostatic forces. This cell-macromolecular nanoarchitectonics is discussed in the latter part of this review. This part includes bottom-up and top-down approaches for constructing highly organized cell-architectures with macromolecules, for regulating cell adhesion pattern and their functions in twodimension, for generating three-dimensional cell architectures on micro-patterned surfaces, and for building synthetic/natural macromolecular modified hybrid biointerfaces.

Incorporation of nonnatural amino acids into proteins is a powerful technique in protein research. Amber suppression has been used to this end, but this strategy does not allow multiple incorporation of nonnatural amino acids into single proteins. In this article, we developed an alternative strategy for nonnatural mutagenesis by using four-base codons. The four-base codons AGGU, CGGU, CCCU, CUCU, CUAU, and GGGU were successfully decoded by the nitrophenylalanyl-tRNA containing the complementary four-base anticodons in an Escherichia coli in vitro translation system. The most efficient four-base decoding was observed for the GGGU codon, which yielded 86% of the full-length protein containing nitrophenylalanine relative to the wild-type protein. Moreover, highly efficient incorporation of two different nonnatural amino acids was achieved by using a set of two four-base codons, CGGG and GGGU. This work shows that the four-base codon strategy is more advantageous than the amber suppression strategy in efficiency and versatility.

R-Helical polypeptides containing a pair of L-1-pyrenylalanine and L-p-nitrophenylalanine that are separated by 0-8 amino acid units were synthesized. The rates of photoinduced electron transfer (ET) from the pyrenyl group to the nitrophenyl group were evaluated from the decay curves of pyrenyl fluorescence recorded at different temperatures from -58 to +30 °C. The rate constants showed a complex dependence on the number of spacer amino acids. In particular, recoveries of the ET rates with increasing the number of spacer amino acids from 1 to 2 and from 5 to 6 were found. The ET rate constants, however, exhibited a simple exponential dependence on the edge-to-edge distance between the two chromophores, with a distance decay factor β ) 0.66 ( 0.1 (Å -1 ). The ET data on the R-helical polypeptides were analyzed on the basis of the tunneling pathway model. The optimum ET pathways from the pyrenyl group to the nitrophenyl group were searched, and the relative values of the ET matrix elements were evaluated for each polypeptide with different number of the spacer units. The calculated distance dependence was in reasonable agreement with the experimental one when jumps through hydrogen bonds were taken into account.

Nonnatural amino acids have been introduced into proteins using expanded protein biosynthesis systems. However, some nonnatural amino acids, especially those containing large aromatic groups, are not efficiently incorporated into proteins. Reduced binding efficiency of aminoacylated tRNAs to elongation factor Tu (EF-Tu) is likely to limit incorporation of large amino acids. Our previous studies suggested that tRNAs carrying large nonnatural amino acids are bound less tightly to EF-Tu than natural amino acids. To expand the availability of nonnatural mutagenesis, EF-Tu from the E. coli translation system was improved to accept such large amino acids. We synthesized EF-Tu mutants, in which the binding pocket of the aminoacyl moiety of aminoacyl-tRNA was enlarged. L-1-Pyrenylalanine, L-2-pyrenylalanine, and DL-2-anthraquinonylalanine, which are hardly or only slightly incorporated with the wild-type EF-Tu, were successfully incorporated into a protein using these EF-Tu mutants.