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.

On the mechanism of the mutagenic action of 5-bromouracil: a DFT study of uracil and 5-bromouracil in a water cluster.

Density functional theory calculations on the canonical (keto) and rare (enol) tautomeric forms of uracil and 5-bromouracil in a cluster consisting of 50 water molecules are presented. The keto form of uracil is favored over the enol tautomer in both the gas phase and solution. However, the presence of the water cluster reverses the tautomeric preference of 5-bromouracil, rendering the rare tautomeric form to be preferred over the canonical form in aqueous solution. This effect is, to a large extent, due to the more favorable water-water interactions in the cluster around 5-bromouracil and can therefore only be obtained by including explicit water-water interactions in the calculations.

A combined DFT/Green's function study on electrical conductivity through DNA duplex between Au electrodes.

Electrical conducting properties of DNA duplexes sandwiched between Au electrodes have been investigated by use of first-principles molecular simulation based on DFT and Green's function to elucidate the origin of their base sequence dependence. The theoretically simulated effects of DNA base sequence on the electrical conducting properties are in qualitative agreement with experiment. The HOMOs localized on Guanine bases have the major contribution to the electrical conductivity through DNA duplexes.

Hybridization energies of double strands composed of DNA, RNA, PNA and LNA.

The electronic properties of double strands composed of trimeric LNA, PNA, DNA and RNA single strands were investigated by density-functional molecular orbital calculations. The computed hybridization energies for the double strands involving PNA or LNA are larger than those for DNA-DNA and RNA-RNA. The larger stability is attributed to the presence of a larger positive charge of the hydrogen atoms contributing to the hydrogen bonds in the PNA-DNA and LNA-DNA double-strands. These results are comparable to the experimental finding that PNA and LNA single strands display high affinity toward a complementary DNA or RNA single strand.

A combined molecular dynamics/density-functional theoretical study on the structure and electronic properties of hydrating water molecules in the minor groove of decameric DNA duplex.

A combined molecular dynamics/density-functional theoretical study was carried out to address the propensity of ambient water to form cross-strand bridging water (CSBW) and their effects on the electronic properties of a fully hydrated DNA duplex 5'-d(CCATTAATGG)(2)-3'. The simulation shows ubiquitous presence of up to five CSBWs along the minor groove, each with residence time ranging from 400 ps to 750 ps. The molecular orbitals localized on these CSBWs are nearly degenerate in energy with the highest occupied molecular orbital of DNA localized on guanine bases, strongly indicating that the hole transport along the guanines is mediated by the ubiquitous CSBWs.

Effect of base mismatch on the electronic properties of DNA-DNA and LNA-DNA double strands: Density-functional theoretical calculations.

The electronic properties of double-stranded octametric DNA-DNA and LNA-DNA with a single-base mismatch were compared with those having fully complementary base pairs to quantify the effect of the base mismatch on hybridization energies (HE). A single T-G mismatch in the LNA-DNA gives rise to a significant reduction in HE, which is consistent with a significant lowering of the melting temperature for mismatched LNA-DNA. By contrast, the hybridization strength of the mismatched DNA-DNA depends strongly on local hydrogen-bonding arrangements in the mispaired T-G. The difference in HE is explained in terms of variation in charge distributions around the hydrogen-bonded base pairs.