Identification of Trypanosoma brucei leucyl-tRNA synthetase inhibitors by pharmacophore- and docking-based virtual screening and synthesis

Human African trypanosomiasis (HAT), caused by the protozoan parasite Trypanosoma brucei, is a neglected fatal disease. Leucyl-tRNA synthetase (LeuRS), which has been successfully applied in the development of antifungal agent, represents a potential antiprotozoal drug target. In this study, a 3D model of T. brucei LeuRS (TbLeuRS) synthetic active site was constructed and subjected to virtual screening using a combination of pharmacophore- and docking-based methods. A new 2-pyrrolinone scaffold was discovered and the structure-activity relationship (SAR) studies aided by the docking model and organic synthesis were carried out. Compounds with various substituents on R(1), R(2) and R(3) were synthesized and their SAR was discussed.     

Discovery and structure–activity study of a novel benzoxaborole anti-inflammatory agent (AN2728) for the potential topical treatment of psoriasis and atopic dermatitis

A series of phenoxy benzoxaboroles were synthesized and screened for their inhibitory activity against PDE4 and cytokine release. 5-(4-Cyanophenoxy)-2,3-dihydro-1-hydroxy-2,1-benzoxaborole (AN2728) showed potent activity both in vitro and in vivo. This compound is now in clinical development for the topical treatment of psoriasis and being pursued for the topical treatment of atopic dermatitis.     

Hemodextrin: a self-assembled cyclodextrin-porphyrin construct that binds dioxygen

Synthetic hemoprotein model compounds are of great interest due to the vital roles and complexities of hemoproteins. This study reports a novel, self-assembled hemoprotein model, hemodextrin. The synthesis and characterization of py-PPCD (2(A)-monopyridylmethyl-perPEGylated-beta-cyclodextrin) (2) is described. The molecular design is based on a pegylated cyclodextrin scaffold that bears both a heme-binding pocket and an axial ligand that binds an iron porphyrin. The binding constant for Fe(III)TPPS [iron(III) meso-tetra(4-sulphonatophenyl)porphyrin] by py-PPCD (2) was determined to be 2 x 10(6) M(-1) at pH 6.0 by observing characteristic changes in the UV-Vis spectrum of the porphyrin. The pyridyl nitrogen of py-PPCD (2) was shown to ligate to the iron center by observing signal changes in the Fe(II)-porphyrin 1H-NMR spectrum. This hemodextrin ensemble was shown to bind dioxygen reversibly and to form a stable ferryl species.     

VIGS技术在甜菜上的应用

病毒诱导基因沉默(VIGS)是一种应用于研究植物基因功能的反向遗传学手段。相对于基因敲除及转基因等方法,它具有时间短、成本低、高通量等优点。随着甜菜全基因组的测序完成,为尽早对大量序列信息进行注释和功能鉴定,急需建立甜菜VIGS体系。本文采用目前应用最广泛的烟草脆裂病毒载体在农杆菌的介导下侵染甜菜幼苗叶片,同时设立对照。提取甜菜幼苗叶片总RNA,并反转录成c DNA,设计特异引物进行RT-PCR检测。结果表明:在侵染植株上检测到了烟草脆裂病毒特异条带,证明该病毒可以对甜菜进行侵染,这一结果为下一步建立甜菜VIGS体系奠定了基础。     

Benzoxaborole antimalarial agents. Part 2: Discovery of fluoro-substituted 7-(2-carboxyethyl)-1,3-dihydro-1-hydroxy-2,1-benzoxaboroles

A series of new boron-containing benzoxaborole compounds was designed and synthesized for a continuing structure-activity relationship (SAR) investigation to assess the antimalarial activity changes derived from side-chain structural variation, substituent modification on the benzene ring and removal of boron from five-membered oxaborole ring. This SAR study demonstrated that boron is required for the antimalarial activity, and discovered that three fluoro-substituted 7-(2-carboxyethyl)-1,3-dihydro-1-hydroxy-2,1-benzoxaboroles (9, 14 and 20) have excellent potencies (IC(50) 0.026-0.209 μM) against Plasmodium falciparum.     

Selective Removal of Aberrant Extender Units by a Type II Thioesterase for Efficient FR-008/Candicidin Biosynthesis in Streptomyces sp. Strain FR-008

Gene fscTE, encoding a putative type II thioesterase (TEII), was associated with the FR-008/candicidin gene cluster. Deletion of fscTE reduced approximately 90% of the FR-008/candicidin production, while the production level was well restored when fscTE was added back to the mutant in trans. FscTE was unable to compensate for the release of the maturely elongated polyketide as site-directed inactivation of the type I thioesterase (TEI) totally abolished FR-008/candicidin production. Direct biochemical analysis of FscTE in parallel with its homologue TylO from the tylosin biosynthetic pathway demonstrated their remarkable preferences for acyl-thioesters (i.e., propionyl-S-N-acetylcysteamine [SNAC] over methylmalonyl-SNAC and acetyl-SNAC over malonyl-SNAC) and thus concluded that TEII could maintain effective polyketide biosynthesis by selectively removing the nonelongatable residues bound to acyl carrier proteins. Overexpression of FscTE under the strong constitutive ermE*p promoter in the wild-type strain did not suppress FR-008/candicidin formation, which confirmed its substrate specificity in vivo. Furthermore, successful complementation of the fscTE mutant was obtained with fscTE and tylO, whereas no complementation was detected with nonribosomal peptide synthetase (NRPS) TEII tycF and srfAD, reflecting substrate specificities of TEIIs distinctive from those of either polyketide synthases or NRPSs.     

Multiple N-glycans cooperate in balancing misfolded BRI1 secretion and ER retention

Key message

N-glycans play a protective or monitoring role according to the folding state of associated protein or the distance from structural defects.

Abstract

Asparagine-linked (Asn/N-) glycosylation is one of the most prevalent and complex protein modifications and the associated N-glycans play crucial roles on protein folding and secretion. The studies have shown that many glycoproteins hold multiple N-glycans, yet little is known about the redundancy of N-glycans on a protein. In this study, we used BRI1 to decipher the roles of N-glycans on protein secretion and function. We found that all 14 potential N-glycosylation sites on BRI1 were occupied with oligosaccharides. The elimination of single N-glycan had no obvious effect on BRI1 secretion or function except N¹⁵⁴-glycan, which resulted in the retention of BRI1 in the endoplasmic reticulum (ER), similar to the loss of multiple highly conserved N-glycans. To misfolded bri1, the absence of N-glycans next to local structural defects enhanced the ER retention and the artificial addition of N-glycan could help the misfolded bri1-GFPs exiting from the ER, indicating that the N-glycans might serve as steric hindrance to protect the structure defects from ER recognition. We also found that the retention of misfolded bri1-9 by lectins and chaperones in the ER relied on the presence of multiple N-glycans distal to the local defects. Our findings revealed that the N-glycans might play a protective or monitoring role according to the folding state of associated protein or the distance from structural defects.