Nonribosomal peptide synthetases (NRPSs) biosynthesize nonribosomal peptide (NRP) natural products, which belong to the most promising resources for drug discovery and development because of their wide range of therapeutic applications. The results of genetic, biochemical, and bioinformatics analyses have enhanced our understanding of the mechanisms of the NRPS machinery. A major goal in NRP biosynthesis is to reprogram the NRPS machinery to enable the biosynthetic production of designed peptides. Reprogramming strategies for the NRPS machinery have progressed considerably in recent years, thereby increasing the yields and generating modified peptides. Here, the recent progress in NRPS reprogramming and its application in peptide synthesis are described.

We recently reported novel purine-based CK2α inhibitors using the solvent ordering–based method as virtual screening. Among these, the X-ray crystal structure of a complex with CK2α was determined. The results...

In contrast to previous SAR studies of aza-compounds (23vs.24 and 25), the present study using analogues (26a–26c, 27c, and 28a–28c) of salacinol (1) revealed an essential role of the thiosugar ring in effectively inhibiting α-glucosidase.

Casein kinase 2 (CK2) is a vital protein kinase that consists of two catalytic subunits (CK2α1 and/or CK2α2) and two regulatory subunits (CK2β). CK2α1 is a drug target for nephritis and cancers, while CK2α2 is a serious off-target because its inhibition causes testicular toxicity. High similarity between the isozymes CK2α1 and CK2α2 make it difficult to design CK2α1-specific inhibitors. Herein, the crystal structures of CK2α1 and CK2α2 complexed with a 3-amino-pyrazole inhibitor revealed the remarkable differences in the protein-inhibitor interaction modes. This inhibitor bound to the ATP binding sites of both isozymes in apparently distinct orientations. In addition, another molecule of this inhibitor bound to CK2α1, but not to CK2α2, at the CK2β protein-protein interface. Binding energy calculations and biochemical experiments suggested that this inhibitor possesses the conventional ATP-competitive characteristics with moderate allosteric function in a molecular glue mechanism. These results will assist the potential design of potent and selective CK2α1 inhibitors.

Four chain-extended analogs (12a-12d) and two related de-O-sulfonated analogs (13a and 13c) by introducing alkyl groups (a: R = C3H7, b R = C6H13, c: R = C8H17, d: R = C10H21) to the side chains of salacinol (1), a natural α-glucosidase inhibitor from Ayurvedic traditional medicine "Salacia", were synthesized. The α-glucosidase inhibitory activities of all the synthesized analogs were evaluated in vitro. Against human intestinal maltase, the inhibitory activities of 12a and 13a with seven-carbon side chain were equal to that of 1. In contrast, analogs (12b-12d, and 13c) exhibited higher level of inhibitory activity against the same enzyme than 1 and had equal or higher potency than those of the clinically used anti-diabetics, voglibose, acarbose, and miglitol. Thus, elongation of the side chains of 1 was effective for specifically increasing the inhibitory activity against human intestinal maltase.

The gatekeeping adenylation (A) domain of the non-ribosomal peptide synthetase (NRPS) selectively incorporates specific proteinogenic/non-proteinogenic amino acid into a growing peptide chain. The EntE of the enterobactin NRPS is a discrete aryl acid A-domain with 2,3-dihydroxybenzoic acid (DHB) substrate specificity. Reprogrammed EntE N235G variant possesses an enlarged substrate recognition site, and is capable of accepting non-native aryl acids. Biochemical characterization of this unique substrate recognition site should provide a better understanding of activi-site microenvironments. Here, we synthesized a non-hydrolysable adenylate analogue with 2-aminobenzoic acid (2-ABA), 3-aminobenzoic acid (3-ABA), and 4-aminobenzoic acid (4-ABA) and used them to calculate the apparent inhibition constants (Kiapp.). Dose-response experiments using 3-ABA-sulfamoyladenosine (AMS) provided Kiapp. values of 596 nM for wild-type EntE and 2.4 nM for the N235G variants. These results suggest that 3-amino group of benzoic acid plays an important role in substrate recognition by the N235G variant. These findings would help designing aryl acid substrates with substituents at the 2- and 3-positions.

Aryl acids are most commonly found in iron-scavenging siderophores but are not limited to them. The nonribosomal peptide synthetase (NRPS) codes of aryl acids remain poorly elucidated relative to those of amino acids. Here, we defined more precisely the role of active-site residues in aryl acid adenylation domains (A-domains) by gradually grafting the NRPS codes used for salicylic acid (Sal) into an archetypal aryl acid A-domain, EntE [specific for the substrate 2,3-dihydroxybenzoic acid (DHB)]. Enzyme kinetics and modeling studies of these EntE variants demonstrated that the NRPS code residues at positions 236, 240, and 339 collectively regulate the substrate specificity toward DHB and Sal. Furthermore, the EntE variants exhibited the ability to activate the non-native aryl acids 3-hydroxybenzoic acid, 3-aminobenzoic acid, 3-fluorobenzoic acid, and 3-chlorobenzoic acid. These studies enhance our knowledge of the NRPS codes of aryl acids and could be exploited to reprogram aryl acid A-domains for non-native aryl acids.

Adenylation (A) domains act as the gatekeepers of non-ribosomal peptide synthetases (NRPSs), ensuring the activation and thioesterification of the correct amino acid/aryl acid building blocks. Aryl acid building blocks are most commonly observed in iron-chelating siderophores, but are not limited to them. Very little is known about the reprogramming of aryl acid A-domains. We show that a single asparagine-to-glycine mutation in an aryl acid A-domain leads to an enzyme that tolerates a wide range of non-native aryl acids. The engineered catalyst is capable of activating non-native aryl acids functionalized with nitro, cyano, bromo, and iodo groups, even though no enzymatic activity of wild-type enzyme was observed toward these substrates. Co-crystal structures with non-hydrolysable aryl-AMP analogues revealed the origins of this expansion of substrate promiscuity, highlighting an enlargement of the substrate binding pocket of the enzyme. Our findings may be exploited to produce diversified aryl acid containing natural products and serve as a template for further directed evolution in combinatorial biosynthesis.

Hydroxychavicol (HC), which is obtained from the leaves of Piper betle LINN. (Piperaceae), inhibits xanthine oxidase (XO) with an IC50 value of 16.7 µM, making it more potent than the clinically used allopurinol (IC50=30.7 µM). Herein, a structure-activity relationship analysis of the polar part analogs of HC was conducted and an inhibitor was discovered with a potency 13 times that of HC. Kinetic studies have revealed that HC and its active analog inhibit XO in an uncompetitive manner. The binding structure prediction of these inhibitor molecules to the XO complex with xanthine suggested that both compounds (HC and its analog) could simultaneously form hydrogen bonds with xanthine and XO.

Solvent dipole ordering virtual screening (SDO-VS) is a virtual screening method that focuses on the shape of the SDO region at the binding site of the protein. In SDO-VS, pseudo molecules (PMs) are generated to reproduce the shape of the SDO region. Compounds that have shapes (or volumes) similar to those of the PMs are then screened from a 3D structure database. The original implementation of SDO-VS involved PMs with only sp3-hybridized carbon atoms. However, utilization of sp2- and sp-hybridized atoms and/or small molecular fragments, in addition to sp3-hybridized atoms, is expected to provide more efficient screening. To this end, this study investigated the effect of sp3-, sp2-, and sp-hybridized atoms and phenyl rings as fragments for PM generation in the SDO-VS method. The screening efficiencies were compared with the original method for several drug target proteins. Overall, this new method improved screening efficiencies, as measured by the area under the curve of the corresponding receiver operating characteristic plots.

We have reviewed chemoinformatics approaches for drug discovery such as aromatic interactions, aromatic clusters, structure generation, virtual screening, de novo design, evolutionary algorithm, inverse-QSPR/QSAR, Monte Carlo, molecular dynamics, fragment molecular orbital method and matched molecular pair analysis from the viewpoint of young researchers. We intend to introduce various fields of chemoinformatics for non-expert researchers. The structure of this review is given as follows: 1. Introduction, 2. Analysis of Aromatic Interactions, 2.1 Aromatic Interactions, 2.2 Aromatic Clusters, 3. Ligand Based Structure Generation, 3.1 Virtual Screening, 3.2 De Novo Ligand Design, 3.3 Combinatorial Explosion, 3.4 Inverse-QSPR/QSAR, 4. Trends in Chemoinformatics-Based De Novo Drug Design, 5. Conformational Search Method Using Genetic Crossover for Bimolecular Systems, 6. Interaction Analysis using Fragment Molecular Orbital Method for Drug Discovery, 7. Matched Molecular Pair Analysis and SAR Analysis by Fragment Molecular Orbital Method, 8. Chemoinformatics Approach in Pharmaceutical Processes, 9. Conclusion.

To develop more potent α-glucosidase inhibitors whose seed-compound is salacinol (1), a potent natural α-glucosidase inhibitor isolated from Salacia reticulata of Ayurvedic traditional medicine, a series of 3'-O-benzylated analogs of 1 were designed with the aid of in silico method. Intensive docking studies proposed several promising compounds. To verify the computational SAR assessments, designed derivatives were synthesized and evaluated in vitro. Their α-glucosidase inhibitory activities against rat intestinal α-glucosidases were so potent as were expected by the docking studies, and all the compounds showed superior inhibitory activities to the original sulfonium sulfate (1). Among the sulfonium salts designed, one with 3'-O-(ortho-nitrobenzyl) moiety (8k) was found to be the most potent, and ca. forty times as potent as 1, the compound being the strongest inhibitor among the sulfonium type inhibitors synthesized so far. [chemical formula]

Casein kinase II (CK2), a serine-threonine protein kinase, is distributed ubiquitously in human body. It exists as a tetramer composed of two catalytic subunits (α and α') and two control subunits (β). Amino acid sequence homology between the catalytic subunit α and α' is very high, 83%. Inhibitors of this enzyme have been explored for cancer, virus infection and glomerulonephritis therapies, and several highly potent compounds have been reported as ATP competitive inhibitors. On the other hand, hematein, a natural compound isolated from Caesalpinia sappan, inhibits CK2α in an ATP uncompetitive manner, whereas it inhibits CK2α' in a competitive manner. We have investigated the binding mode of hematein to both isozymes using docking studies followed by the binding energy analysis with the MM/PBSA method and the simulated annealing simulation. The results suggested that hematein could bind to the ATP binding site of the both isozymes. In addition, it might bind to the allosteric site and the substrate binding site of CK2α.

Binding free energy ΔGbind of a ligand to the target protein is a physicochemical quantity which closely relates to a drug activity, and prediction of ΔGbind with accuracy leads to an efficient drug design. As a method to calculate ΔΔGbind, difference of ΔGbind between two ligands, FEP (free energy perturbation) and TI (thermodynamic integration) methods are well known. Theoretically, application of these methods are limited to the system where an energy difference is small, ~2 kcal/mol. Recently, Jorgensen et al. have applied these methods to a lead optimization study of HIV reverse transcriptase inhibitors, and succeeded in obtaining a qualitative relationship between the predicted and experimental values. However, it is desirable to establish an appropriate calculation procedure of these methods which reproduces experimental ΔΔGbind quantitatively. In this study, we applied the FEP/TI methods to the FXa (activated blood coagulation factor X) inhibitors, where one hydrogen atom on an inhibitor molecule was replaced with a chlorine atom. Several calculation procedures have been tested.

計算機資源の向上と計算手法の発達により、従来では困難であった高精度な分子軌道計算による相互作用解析が、タンパク質－薬物複合体などの巨大分子系においても一般化しつつある。これらの知見は、構造に基づくドラッグデザインに大きな知見をもたらすと期待がされており、特に古典的な力場計算では考慮していなかった、CH-O相互作用やCl-pi相互作用などが結合に寄与することが重要視されてきている。巨大分子系の分子軌道計算は、近似計算の方のひとつであるフラグメント分子軌道法（FMO法）によって行われることが多い。FMO法の利点は、単純に計算時間が短縮できるという点だけではなく、リガンドと各アミノ酸残基との相互作用など通常の分子軌道計算では求めることが困難な要素を得ることが可能であり、それにより力場法で行っていたことに近い感覚で解析が可能であるという点が挙げられる。 すでにFMO法に関するインターフェースはABINIT-MPなどいくつか存在し

計算機資源の向上に伴い、タンパク質－薬物複合体などの巨大分子系においても高精度な分子軌道計算による相互作用解析が浸透しつつある。それにより、従来の古典的な力場計算では考慮していなかった、CH-O相互作用やCL-π相互作用などによる結合への寄与が明らかになってきている。しかし巨大分子系の分子軌道計算は、通常の計算方法では現実的な計算時間で解析を行うことが困難なため、近似計算の方のひとつであるフラグメント分子軌道法（FMO法）によって行われることが多い。FMO法の利点は、単純な計算時間の短縮できるという点だけではなく、アミノ酸残基ごとの相互作用など通常の分子軌道計算では求めることが困難な要素を得ることが可能であり、それにより力場法で行っていたことに近い感覚で解析が可能であるという点が挙げられる。 現在FMO法による計算が可能なツールとしてはGAMESSやABINIT-MP, PAICSなどが存在しており、GAMESS/FMOではFMO法の開発者らによる最新の

【目的】新規に阻害剤を設計する際には、阻害剤の結合自由エネルギーを予測することが重要となる。本研究で用いたCK2阻害剤であるCC4791およびCC4820の結合自由エネルギーはほぼ同等であるが、小さな置換基変化（イソプロピル基とシクロペンチル基）にも関わらず、熱力学的プロファイル（エンタルピー・エントロピーの寄与度）が異なることが熱測定により観測されている。構造の差がどのような要因で熱力学的な差を生じさせているのか、計算化学的に考察を行った。 【方法】それぞれの複合体に対し、阻害剤の周囲25?に対し水分子を発生させた系で分子動力学（MD）計算を行い、このトラジェクトリーに対し溶媒効果を含めた相互作用計算を行った。また、阻害剤の結合状態と水中との運動性の差を解析するため、阻害剤を半径25?の球状の水分子クラスター中に配置した系でもMD計算を行い、置換基の二面角を中心に運動性を検討した。 【結果と考察】相互作用計算の結果、CC4

【目的】インドやスリランカの伝統医学アーユルヴェーダでは、Salacia属植物が糖尿病の特効薬として用いられている。本植物から単離されるチオ糖スルホニウム硫酸分子内塩構造を持つsalacinolやkotalanolは、？グルコシダーゼを阻害することによる糖吸収抑制作用を有しており、同メカニズムに基づく抗糖尿病薬であるacarboseやvogliboseに匹敵する？グルコシダーゼ阻害活性を有している。本研究では、これらの化合物のタンパク質結合構造をもとに新規阻害剤の設計をするために、両化合物のドッキングシミュレーションを実施した。 【方法】まず、？グルコシダーゼの１つであるマルターゼグルコアミラーゼのN末端側触媒ドメインとacarbose及びcasuarineとの複合体構造（PDBID：2QMJおよび3CTT）を再現できるドッキングシミュレーション条件を探索した。次にそのシミュレーション条件を用いて、salacinol及びkotalanolの結合様式を推定した。 【結果】結合シミュレーションの結果、salacinol及び

【目的】タンパク質と低分子との結合親和力を高精度に計算することは、ターゲットの構造に基づく薬物設計を行うために最も重要な要素のひとつである。定量性に最も優れた非経験的分子軌道法を、タンパク質などの大きな系に適用する計算手法として、Fragment MO(FMO)法が開発されている。タンパク質のFMO法による計算はすでに浸透しつつあるが、一般的に、タンパク質と低分子との相互作用には分散力が大きく寄与することが、MP2レベルなどの電子相関を考慮したFMO法のエネルギー計算から明らかとなってきている。しかし相互作用を精密に計算する前段階である構造最適化は、計算コストの問題から電子相関を考慮しないHFレベルで計算されているのが現状である。本研究ではMP2レベルの計算が構造に与える影響について検討を行った。 【方法】GAMESS/FMOを用いて、FK506 Binding Protein(FKBP)とその4つの阻害剤との各複合体をFMO-MP2/6-31Gレベル、および比較のためにFMO-HF/3-21Gレベルで構造最

バーチャルスクリーニングの高精度化のため、COMBINE解析法を応用した受容体特異的なスコア関数を考案した。バーチャルスクリーニングでは化合物の活性値予測と結合様式予測の両者が重要となるが、今回はその検証の一つとして、後者の結合様式予測に関して、HIV ptorease およびAdenosine deaminaseとその阻害薬を用いて予測が可能か検討した。 （英文）

To improve accuracy of virtual screening in which candidate medical compounds were searched fast by computer, COMBINE method that is one of the Quantitative Structure-Activity Relationship (QSAR) was applied as the scoring function. As the results of several validations, active compounds were able to be extracted at high throughput. Furthermore, binding mode of the compounds to their target protein could be predicted at the same time.