A Ligation and Photorelease Strategy for the Temporal and Spatial Control of Protein Function in Living Cells

Development of O-acyl isopeptide method

During over a decade of study on aspartic protease inhibitors and water-soluble prodrugs, in 2003, we discovered that the presence of an O-acyl instead of N-acyl residue within the peptide backbone significantly changed the secondary structure of the native peptide. In addition, the target peptide was subsequently generated by an O-N intramolecular acyl migration reaction. These findings led to the development of a novel method, called "O-acyl isopeptide method," for the synthesis of peptides containing difficult sequence. Further application of the method to Alzheimer's Abeta1-42 revealed that the O-acyl isopeptide of Abeta1-42 could be effectively synthesized and stored without spontaneous self-assembly. Intact monomer Abeta1-42 could then be obtained from the isopeptide under physiological experimental conditions. We named the O-acyl isopeptide as "Click Peptide," because of its "quick and easy one-way conversion" to the parent Abeta1- 42. Application of the click peptide has provided a new basis for the investigation of the biological functions of Abeta1-42 by inducible activation of its self-assembly. The O-acyl isopeptide method has further evolved as a general method for peptides synthesis with our recent developments of "O-acyl isodipeptide units" and "racemization-free segment condensation methodology." Isodipeptide units have enabled routine use of the O-acyl isopeptide method by avoiding the often difficult esterification reaction on resin. "Racemizationfree segment condensation methodology" has been achieved by employing N-segments possessing a C-terminal urethaneprotected O-acyl Ser/Thr residues. The synthesis of long peptides/proteins by racemization-free segment condensation has thus become possible at Ser/Thr residues instead of Cterminal Gly/Pro residues. As the O-acyl isopeptide method becomes more widely utilized, we have composed this review to facilitate its application for the production of peptides and proteins.

Triptycene-Based Expanded Oxacalixarenes: Synthesis, Structure, and Tubular Assemblies in the Solid State

Owing to the unique 3D rigid structure of triptycene, two novel expanded oxacalixarenes 5a and 5b as a pair of diastereomers were efficiently synthesized in a single step by the SNAr reaction of 2,7-dihydroxytriptycene with 2,3,5,6-tetrachloropyridine in the presence of cesium carbonate. Similarly, two pairs of other triptycene-based expanded oxaxalixaenes 7a,7b and 9a,9b could also be obtained by the SNAr reactions of 2,7-dihydroxytriptycene with 1,5-difluoro-2,4-dinitrobenzene and cyanuric chloride, respectively. The structures of the expanded oxacalixarenes were studied by NMR, MS spectra, and X-ray crystal structure analyses. It was found that the expanded oxacalixarene 9b showed a dynamic interconversion between boat and chair conformations. Moreover, we also found that the expanded oxacalixarenes 5a, 5b, and 9a could all assemble into organic tubular structures and further porous architectures in the solid state, in which chlorine bonding, such as C-Cl...Cl, C-Cl...O, and C-Cl...pi interactions, played an important role.

Controlling multiple fluorescent signal output in cyclic peptide-based supramolecular systems

A multicomponent equilibrium network based on self-assembling alpha,gamma-cyclic peptides with controlled fluorescence output is described. The network takes advantage of the large association constant of alpha,gamma-cyclic peptides and the controlled formation homo- and heterodimers, making use for the first time of excimer/FRET effects in conjunction for studying complex interaction networks. In addition, we study the Dapoxyl/pyrene FRET pair for the first time.

Selective Labeling of Proteins by Using Protein Farnesyltransferase

The challenging task of identifying and studying protein function has been greatly aided by labeling proteins with reporter groups. Here, we present a strategy that utilizes an enzyme that labels a four-residue sequence appended onto the C terminus of a protein, with an alkyne-containing substrate. By using a bio-orthogonal cycloaddition reaction, a fluorophore that carried an azide moiety was then covalently coupled to the alkyne appended on the protein. FRET was used to calculate a Förster (R) distance of 40 A between the eGFP chromophore and the newly appended Texas Red fluorophore. This experimental value is in good agreement with the predicted R value determined by using molecular modeling. The small recognition tag, the high specificity of the enzyme, and the orthogonal nature of the derivatization reaction will make this approach highly useful in protein chemistry.

Photochemical control of biological processes

Photochemical regulation of biological processes offers a high level of control to study intracellular mechanisms with unprecedented spatial and temporal resolution. This report summarizes the advances made in recent years, focusing predominantly on the in vivo regulation of gene function using irradiation with UV light. The majority of the described applications entail the utilization of photocaging groups installed either on a small molecule modulator of biomolecular function or directly on a biological macromolecule itself.

Conformational Analysis of Some C2-Symmetric Cyclic Peptides Containing Tetrahydrofuran Amino Acids

Cyclic oligomers of tetrahydrofuran amino acids, cyclo-(Taa1-Leu-Val)2 (left), cyclo-(Taa2-Leu-Val)2 (middle), and cyclo-(Taa2-Phe-Leu)2 (right), displayed well-defined intramolecularly hydrogen-bonded structures with distorted "beta-beta corner" motifs similar to the tennis ball seam.