An expanded genetic code facilitates antibody chemical conjugation involving the lambda light chain.

Most of the currently approved therapeutic antibodies are of the immunoglobulin gamma (IgG) κ isotype, leaving a vast opportunity for the use of IgGλ in medical treatments. The incorporation of designer amino acids into antibodies enables efficient and precise manufacturing of antibody chemical conjugates. Useful conjugation sites have been explored in the constant domain of the human κ-light chain (LCκ), which is no more than 38% identical to its LCλ counterpart in amino acid sequence. In the present study, we used an expanded genetic code for site-specifically incorporating Nε-(o-azidobenzyloxycarbonyl)-l-lysine (o-Az-Z-Lys) into the antigen-binding fragment (Fab) of an IgGλ, cixutumumab. Ten sites in the LCλ constant domain were found to support efficient chemical conjugation exploiting the bio-orthogonal azido chemistry. Most of the identified positions are located in regions that differ between the two light chain isotypes, thus being specific to the λ isotype. Finally, o-Az-Z-Lys was incorporated into the Fab fragments of cixutumumab and trastuzumab to chemically combine them; the resulting bispecific Fab-dimers showed a strong antagonistic activity against a cancer cell line. The present results expand the utility of the chemical conjugation method to the whole spectrum of humanized antibodies, including the λ isotype.

Extensive Survey of Antibody Invariant Positions for Efficient Chemical Conjugation Using Expanded Genetic Codes.

The site-specific chemical conjugation of proteins, following synthesis with an expanded genetic code, promises to advance antibody-based technologies, including antibody drug conjugation and the creation of bispecific Fab dimers. The incorporation of non-natural amino acids into antibodies not only guarantees site specificity but also allows the use of bio-orthogonal chemistry. However, the efficiency of amino acid incorporation fluctuates significantly among different sites, thereby hampering the identification of useful conjugation sites. In this study, we applied the codon reassignment technology to achieve the robust and efficient synthesis of chemically functionalized antibodies containing Nε-(o-azidobenzyloxycarbonyl)-l-lysine (o-Az-Z-Lys) at defined positions. This lysine derivative has a bio-orthogonally reactive group at the end of a long side chain, enabling identification of multiple new positions in Fab-constant domains, allowing chemical conjugation with high efficiency. An X-ray crystallographic study of a Fab variant with o-Az-Z-Lys revealed high-level exposure of the azido group to solvent, with six of the identified positions subsequently used to engineer "Variabodies", a novel antibody format allowing various connections between two Fab molecules. Our findings indicated that some of the created Variabodies exhibited agonistic activity in cultured cells as opposed to the antagonistic nature of antibodies. These results showed that our approach greatly enhanced the availability of antibodies for chemical conjugation and might aid in the development of new therapeutic antibodies.

Latching operation in a tunable wavelength filter using Si sampled grating waveguide with ferroelectric liquid crystal cladding.

A tunable wavelength filter fabricated with a latching function is proposed. The proposed tunable wavelength filter consists of a silicon sampled grating waveguide and ferro-electric liquid crystal (FLC) cladding. The sampled grating waveguide in a silicon-on-insulator (SOI) wafer achieved narrower stop bands than that with the conventional uniform grating structure. Enhanced wavelength shift was also obtained due to the increased effect in FLC by using a thinner silicon core. Bistable switching operation with the fabricated device, which was latching without state-sustaining power, was successfully demonstrated. Its switching and latching characteristics are also reported.

Three- and four-body corrected fragment molecular orbital calculations with a novel subdividing fragmentation method applicable to structure-based drug design.

We develop an inter-fragment interaction energy (IFIE) analysis based on the three- and four-body corrected fragment molecular orbital (FMO3 and FMO4) method to evaluate the interactions of functional group units in structure-based drug design context. The novel subdividing fragmentation method for a ligand (in units of their functional groups) and amino acid residues (in units of their main and side chains) enables us to understand the ligand-binding mechanism in more detail without sacrificing chemical accuracy of the total energy and IFIEs by using the FMO4 method. We perform FMO4 calculations with the second order Møller-Plesset perturbation theory for an estrogen receptor (ER) and the 17ß-estradiol (EST) complex using the proposed fragmentation method and assess the interaction for each ligand-binding site by the FMO4-IFIE analysis. When the steroidal EST is divided into two functional units including "A ring" and "D ring", respectively, the FMO4-IFIE analysis reveals their binding affinity with surrounding fragments of the amino acid residues; the "A ring" of EST has polarization interaction with the main chain of Thr347 and two hydrogen bonds with the side chains of Glu353 and Arg394; the "D ring" of EST has a hydrogen bond with the side chain of His524. In particular, the CH/π interactions of the "A ring" of EST with the side chains of Leu387 and Phe404 are easily identified in cooperation with the CHPI program. The FMO4-IFIE analysis using our novel subdividing fragmentation method, which provides higher resolution than the conventional IFIE analysis in units of ligand and each amino acid reside in the framework of two-body approximation, is a useful tool for revealing ligand-binding mechanism and would be applicable to rational drug design such as structure-based drug design and fragment-based drug design.

Intra- and intermolecular interactions between cyclic-AMP receptor protein and DNA: ab initio fragment molecular orbital study.

The ab initio fragment molecular orbital (FMO) calculations were performed for the cAMP receptor protein (CRP) complexed with a cAMP and DNA duplex to elucidate their sequence-specific binding and the stability of the DNA duplex, as determined by analysis of their inter- and intramolecular interactions. Calculations were performed with the AMBER94 force field and at the HF and MP2 levels with several basis sets. The interfragment interaction energies (IFIEs) were analyzed for interactions of CRP-cAMP with each base pair, DNA duplex with each amino acid residue, and each base pair with each residue. In addition, base-base interactions were analyzed including hydrogen bonding and stacking of DNA. In the interaction between DNA and CRP-cAMP, there was a significant charge transfer (CT) from the DNA to CRP, and this CT interaction played an important role as well as the electrostatic interactions. It is necessary to apply a quantum mechanical approach beyond the "classical" force-field approach to describe the sequence specificity. In the DNA intramolecular interaction, the dispersion interactions dominated the stabilization of the base-pair stacking interactions. Strong, attractive 1,2-stacking interactions and weak, repulsive 1,3-stacking interactions were observed. Comparison of the intramolecular interactions of free and complexed DNA revealed that the base-pairing interactions were stronger, and the stacking interactions were weaker, in the complexed structure. Therefore, the DNA duplex stability appears to change due to both the electrostatic and the CT interactions that take place under conditions of DNA-CRP binding.