Kaori Fukuzawa

Fragment molecular orbital method: use of approximate electrostatic potential

Recently, we have proposed the fragment molecular orbital (FMO) method; an approximate MO method for calculating large molecules such as proteins. The method has been shown to reproduce ab initio total energies and geometries of molecules in good accuracy. The most time consuming part in the method, the calculations of environmental electrostatic potentials, were speeded up by employing the Mulliken approximation for two-electron integrals and a fractional point charge approximation. Numerical calculations on several polypeptides revealed that the approximations brought no significant loss of accuracy in the total energy of molecules and were of practical use.

Ab initio quantum mechanical study of the binding energies of human estrogen receptor α with its ligands: An application of fragment molecular orbital method

We have theoretically examined the relative binding affinities (RBA) of typical ligands, 17β‐estradiol (EST), 17α‐estradiol (ESTA), genistein (GEN), raloxifene (RAL), 4‐hydroxytamoxifen (OHT), tamoxifen (TAM), clomifene (CLO), 4‐hydroxyclomifene (OHC), diethylstilbestrol (DES), bisphenol A (BISA), and bisphenol F (BISF), to the α‐subtype of the human estrogen receptor ligand‐binding domain (hERα LBD), by calculating their binding energies. The ab initio fragment molecular orbital (FMO) method, which we have recently proposed for the calculations of macromolecules such as proteins, was applied at the HF/STO‐3G level. The receptor protein was primarily modeled by 50 amino acid residues surrounding the ligand. The number of atoms in these model complexes is about 850, including hydrogen atoms. For the complexes with EST, RAL, OHT, and DES, the binding energies were calculated again with the entire ERαLBD consisting of 241 residues or about 4000 atoms. No significant difference was found in the calculated binding energies between the model and the real protein complexes. This indicates that the binding between the protein and its ligands is well characterized by the model protein with the 50 residues. The calculated binding energies relative to EST were very well correlated with the experimental RBA (the correlation coefficient r = 0.837) for the ligands studied in this work. We also found that the charge transfer between ER and ligands is significant on ER–ligand binding. To our knowledge, this is the first achievement of ab initio quantum mechanical calculations of large molecules such as the entire ERαLBD protein.

Fragment molecular orbital method: application to molecular dynamics simulation, 'ab initio FMO-MD'

Abstract A quantum molecular simulation method applicable to biological molecules is proposed. Ab initio fragment molecular orbital method-based molecular dynamics (FMO-MD) combines molecular dynamics simulation with the ab initio fragment molecular orbital method. Here, FMO computes the force acting on each atom’s nucleus while MD computes the nuclei’s time-dependent evolutions. FMO-MD successfully simulated a small polypeptide, demonstrating the method’s applicability to biological molecules.

VISCANA : Visualized cluster analysis of protein-ligand interaction based on the ab initio fragment molecular orbital method for virtual ligand screening

We have developed a visualized cluster analysis of protein-ligand interaction (VISCANA) that analyzes the pattern of the interaction of the receptor and ligand on the basis of quantum theory for virtual ligand screening. Kitaura et al. (Chem. Phys. Lett. 1999, 312, 319-324.) have proposed an ab initio fragment molecular orbital (FMO) method by which large molecules such as proteins can be easily treated with chemical accuracy. In the FMO method, a total energy of the molecule is evaluated by summation of fragment energies and interfragment interaction energies (IFIEs). In this paper, we have proposed a cluster analysis using the dissimilarity that is defined as the squared Euclidean distance between IFIEs of two ligands. Although the result of an ordered table by clustering is still a massive collection of numbers, we combine a clustering method with a graphical representation of the IFIEs by representing each data point with colors that quantitatively and qualitatively reflect the IFIEs. We applied VISCANA to a docking study of pharmacophores of the human estrogen receptor alpha ligand-binding domain (57 amino acid residues). By using VISCANA, we could classify even structurally different ligands into functionally similar clusters according to the interaction pattern of a ligand and amino acid residues of the receptor protein. In addition, VISCANA could estimate the correct docking conformation by analyzing patterns of the receptor-ligand interactions of some conformations through the docking calculation.

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.

Ab initio fragment molecular orbital study of molecular interactions in liganded retinoid X receptor: specification of residues associated with ligand inducible information transmission.

The ab initio fragment molecular orbital calculations were performed for the alpha-subtype of the human retinoid X receptor (hRXRalpha) complex with its natural ligand 9- cis retinoic acid (9cRA) to quantitatively specify the key residues with important roles for the ligand inducible information transmission of RXR. In the RXR-9cRA complex, the transactivation helix 12 (H12) adopts a canonical agonist conformation, which just corresponds to the transcriptional activation function 2 activating domain core (AF2C). Through the analyses of molecular interactions by the second-order Møller-Plesset perturbation (MP2) method, it was proved that Trp305 and Leu436 of the AF2C binding pocket would be important for the stabilization of the H12 canonical agonist conformation, and, at the same time, for the recognition of the 9cRA molecule. Besides, through the analyses of orbital interactions by the local MP2 (LMP2) method, it was found that Trp305 and Leu436 would recognize the 9cRA molecule especially at its C19 methyl group, which has been most notably targeted to modify for agonist and antagonist design. Moreover, on the basis of the relationships of molecular interactions, it was suggested that the interactions of Trp305 and Leu436 with AF2C residues would be significantly influenced by the interactions of Trp305 and Leu436 with 9cRA. Taken together, our findings quantitatively demonstrated that Trp305 and Leu436 would be the possible key residues for the information transmission in liganded RXR, accounting for their importance suggested by experiments. Altogether, these results substantiated that our approach is useful for the understanding of the detailed molecular mechanism underlying the transcriptional regulation of RXR and related nuclear receptors at the quantum mechanical level.

Theoretical analysis of binding specificity of influenza viral hemagglutinin to avian and human receptors based on the fragment molecular orbital method

The hemagglutinin (HA) protein of the influenza virus binds to the host cell receptor in the early stage of viral infection. A change in binding specificity from avian 2-3 to human 2-6 receptor is essential for optimal human-to-human transmission and pandemics. Therefore, it is important to reveal the key factors governing the binding affinity of HA-receptor complex at the molecular level for the understanding and prediction of influenza pandemics. In this work, on the basis of ab initio fragment molecular orbital (FMO) method, we have carried out the interaction energy analysis of HA-receptor complexes to quantitatively elucidate the binding specificity of HAs to avian and human receptors. To discuss the binding property of influenza HA comprehensively, a number of HAs from human H1, swine H1, avian H3 and avian H5 viruses were analyzed. We performed detailed investigations about the interaction patterns of complexes of various HAs and receptor analogues, and revealed that intra-molecular interactions between conserved residues in HA play an important role for HA-receptor binding. These results may provide a hint to understand the role of conserved acidic residues at the receptor binding site which are destabilized by the electrostatic repulsion with sialic acid. The calculated binding energies and interaction patterns between receptor and HAs are consistent with the binding specificities of each HA and thus explain the receptor binding mechanism. The calculated results in the present analysis have provided a number of viewpoints regarding the models for the HA-receptor binding specificity associated with mutated residues. Examples include the role of Glu190 and Gln226 for the binding specificity of H5 HA. Since H5 HA has not yet been adapted to human receptor and the mechanism of the specificity change is unknown, this result is helpful for the prediction of the change in receptor specificity associated with forthcoming possible pandemics.

Possibility of Mutation Prediction of Influenza Hemagglutinin by Combination of Hemadsorption Experiment and Quantum Chemical Calculation for Antibody Binding

We have performed a quantum-chemical MP2/6-31G* calculation for the hemagglutinin (HA) antigen-antibody system of the H3N2 influenza virus with the fragment molecular orbital method, which provides one of the worlds largest ab initio electron-correlated calculations for biomolecular systems. On the basis of the calculated interfragment interaction energies (IFIEs) representing the molecular interactions between the amino acid residues in the antigen-antibody complex, we have identified those residues in the antigenic region E of HA protein that are significantly recognized by the Fab fragment of antibody with strongly attractive interactions. Combining these IFIE results with those of hemadsorption experiments by which the mutation-prohibited sites are specified has enabled us to explain most of the historical mutation data (five of six residues), which would thus provide a promising method for predicting the HA residues that have a high probability of forthcoming mutation.

Fragment molecular orbital calculations on red fluorescent proteins (DsRed and mFruits).

We have performed a series of fragment molecular orbital (FMO) calculations for a family of red fluorescent proteins, DsRed and mFruits. The electronic transition energies were evaluated by the method of configuration interaction singles with perturbative doubles [CIS(D)] including higher-order corrections. The calculated values were in good agreement with the corresponding experimental peak values of spectra. Additionally, the chromophore environment was systematically analyzed in terms of the interaction energies between the pigment moiety and neighboring residues. It was theoretically revealed that the electrostatic interactions play a dominant role in the DsRed chromophore, whereas the color tunings in mFruits are controlled in a more delicate fashion.

Discovery of boron-conjugated 4-anilinoquinazoline as a prolonged inhibitor of EGFR tyrosine kinase.

Boron-conjugated 4-anilinoquinazolines were designed and synthesized as inhibitors of EGFR tyrosine kinase with possible covalent bond interactions between the boron atom and the nucleophilic groups of the EGFR kinase domain. Among the compounds synthesized, compounds 6c, 7b, and 7d reduced the EGF-mediated phosphorylation of EGFR tyrosine kinase and its downstream kinases including ERK and Akt in A431 cells. The cell growth was inhibited by these compounds through arrest of G1 cell cycle, which induced apoptosis. A time-dependent in vitro preincubation assay demonstrated the irreversible inhibition of compound 7d against EGFR tyrosine kinase. Quantum mechanical docking simulation revealed that the boronic acid moiety of compound 7d formed a covalent B-O bond with Asp800 in addition to hydrogen bonds with Asp800 and Cys797, which may cause the prolonged inhibition of compound 7d toward EGFR tyrosine kinase.