A unique insertion of low complexity amino acid sequence underlies protein-protein interaction in human malaria parasite orotate phosphoribosyltransferase and orotidine 5'-monophosphate decarboxylase

Objective:To investigate the multienzyine complex formation of human malaria parasite Plasmodium falciparum[P.falciparum)orotate phosphoribosyltransferase(OPRT)and orotidine5'-monophosphate decarboxylase(OMPDC),the fifth and sixth enzyme of the de novo pyrimidine biosynthetic palhway.Previously,we have clearly established that the two enzymes in the malaria parasite exist physically as a heterotetrameric(OPRT)_2(OMPDG)_2 complex containing two subunits each of OPRT and OMPDC.and that the complex have catalytic kinetic advantages over the monofunetional enzyme.Methods:Both enzymes were cloned and expressed as recombinant proteins.The protein-protein interaction in the enzyme complex was identified using bifunctionul chemical cross-linker,liquid chromatography-mass spectrometric analysis and homology modeling,Results:The unique insertions of low complexity region at the a 2 and a 5 helices of the parasite OMPDC,characterized by single amino acid repeat sequence which was not found in homologous proteins from other organisms,was located on the OPRT-OMPDC interface.The structural models for the protein-prolein interaction of the helerotetrameric(OPRT)_2(OMPDC)_2multienzyme complex were proposed.Conclusions:Based on the proteomic data and structural modeling,it is surmised that the human malaria parasite low complexity region is responsible for the OPRT-OMPDC interaction.The structural complex of the parasite enzymes,thus,represents an efficient functional kinetic advantage,which in line with co-localization principles of evolutional origin,and allosteric control in protein-protein-interactions.     

Lens cholesterol biosynthesis inhibition: A common mechanism of cataract formation in laboratory animals by pharmaceutical products

CJ‐12,918, a 5‐lipoxygenase (5‐LO) inhibitor, caused cataracts during a 1‐month safety assessment studies in rats whereas the structurally similar ZD‐2138 was without effect. For CJ‐12,918 analogs, blocking different sites of metabolic liability reduced (CJ‐13,454) and eliminated (CJ‐13,610) cataract formation in both rats and dogs. Using this chemical series as a test set, models and mechanisms of toxicity were first explored by testing the utility of ex vivo rat lens explant cultures as a safety screen. This model overpredicted the cataractogenic potential of ZD‐2138 due to appreciably high lens drug levels and was abandoned in favor of a mechanism‐based screen. Perturbations in lens sterol content, from a decline in lathosterol content, preceded cataract formation suggesting CJ‐12,918 inhibited lens cholesterol biosynthesis (LCB). A 2‐day bioassay in rats using ex vivo LCB assessments showed that the level of LCB inhibition was correlated with incidence of cataract formation in animal studies by these 5‐LO inhibitors. Thereafter, this 2‐day bioassay was applied to other pharmaceutical programs (neuronal nitric oxide synthase, sorbitol dehydrogenase inhibitor, squalene synthetase inhibitor and stearoyl‐CoA desaturase‐1 inhibitors/D₄ antagonists) that demonstrated cataract formation in either rats or dogs. LCB inhibition >40% was associated with a high incidence of cataract formation in both rats and dogs that was species specific. Bioassay sensitivity/specificity were further explored with positive (RGH‐6201/ciglitazone/U18666A) and negative (tamoxifen/naphthalene/galactose) mechanistic controls. This body of work over two decades shows that LCB inhibition was a common mechanism of cataract formation by pharmaceutical agents and defined a level of inhibition >40% that was typically associated with causing cataracts in safety assessment studies typically ≥1 month.     

MicroRNA调控药用植物萜类生物合成研究进展

萜类化合物是药用植物中一类重要的次生代谢产物,对癌症、心血管疾病、疟疾和阿尔茨海默病等多种疾病有效。微RNA (microRNA,miRNA)是一种非编码单链小分子RNA,在转录后水平通过降解目标mRNA或阻断翻译发挥作用。miRNA可以通过作用于萜类生物合成途径的结构基因或转录因子调控药用植物萜类的生物合成。目前,萜类生物合成途径的上游部分研究比较清楚,很多关键酶的编码基因已经被克隆,有的酶分子的空间结构也已被解析,针对参与基因表达调控的转录因子也有一些研究,但对非编码RNA,特别是miRNA参与萜类生物合成的研究较少。对国内外近10年有关miRNA参与萜类生物合成的研究进行综述,以期为高效获取萜类活性成分和阐明萜类药效物质的生物合成提供参考。