Mechanisms of Polyketide, Amino Acid and Polypeptide Biosynthesis

化学生物学、多肽合成和天然产物研究的主要目标涉及有机化学（如合成、光谱分析）和生物化学（如分子生物学、蛋白质表征、酶抑制和蛋白质结构）中使用的方法的结合。细菌抗菌肽（氨基酸聚合物）的合成、构效关系及机理研究主要分为两个方面。真菌聚酮合成酶（PKS）是一种来自真菌的大蛋白，它可以聚合乙酸以产生生物活性分子，其中一些是重要的人类药物。就抗菌肽的背景而言，超过50%的医院获得性感染具有抗生素耐药性，相应的细菌病原体现在构成严重的健康威胁。幸运的是，某些肽可以非常有效地摧毁这些病原体。我们的目标是了解细菌抗菌肽的结构和作用机制。细菌产生的抗菌肽通常比传统抗生素更有效，可以杀死耐药病原体，并且经常与目标细菌膜上的受体分子结合。它们可以由核糖体产生（细菌素）或由非核糖体肽合成酶（如脂肽）产生。一个中心主题是对这类肽进行合成修饰，使其更容易获得，可用于人体摧毁耐药病原体的类似物。目标包括抗生素（nisin），硫到a-C连接肽（thuricins）和套索肽（microcin J25）。一个关键的目标是了解这些肽与脂质和受体的相互作用，以及导致细菌细胞死亡的膜孔结构。目标包括脂肽（tridecaptin）和环细菌素（carnocyclin A）。产生肉毒杆菌素A （MicocinTM）的细菌种类已被批准用于美国和加拿大的肉类保存食品中，并且具有很大的潜力作为传统抗生素耐药感染的治疗药物。在背景方面，聚酮是由被称为聚酮合成酶（PKS）的大（bbb200 kDa）酶（蛋白质）构建的次级代谢物，其操作类似于脂肪酸合成酶。超过20种重要的药物是由已知的聚酮衍生而来的。它们的最终功能是将醋酸酯、丙酸酯或其他小前体聚合成具有特定长度、功能和立体化学的链。我们的目标是阐明高度还原真菌PKS酶的机制，这是一种非凡的分子机器。靶标包括组装洛伐他汀（一种降胆固醇药物和辛伐他汀（Zocor）的前体）、马西芹素（抑制HIV）、脱氢曲vularin（一种免疫调节剂植物毒素）、细胞松弛素E（一种抗血管生成抗癌剂）和hypothemycin（一种激酶抑制剂和抗癌候选者）的酶。

The major objectives of the proposed research in chemical biology, peptide synthesis and natural products involve combination of methods used in organic chemistry (e.g. synthesis, spectroscopic analysis) and biochemistry (e.g. molecular biology, protein characterization, enzyme inhibition and structure of proteins). It is mostly divided into two areas: I. synthesis, structure-activity relationships and mechanism of bacterial antimicrobial peptides (polymers of amino acids) and II. mechanism of fungal polyketide synthases (PKS), large proteins from fungi that polymerize acetic acid to make bioactive molecules, some of which are important human drugs. In terms of background for the antimicrobial peptides, over 50% of hospital-acquired infections are antibiotic-resistant, and the corresponding bacterial pathogens now pose a serious health threat. Fortunately, certain peptides can destroy these pathogens very effectively. Our goals are to understand the structures and mechanisms of action of antimicrobial peptides from bacteria. Antimicrobial peptides produced by bacteria are often orders of magnitude more potent than conventional antibiotics, can kill resistant pathogens, and frequently bind a receptor molecule in the membrane of target bacteria. They can be ribosomally made (bacteriocins) or produced by nonribosomal peptide synthases (e.g. lipopeptides). A central theme is synthetic modification of such peptides to make simpler accessible analogs that can be used in humans to destroy resistant pathogens. The targets include lantibiotics (nisin), sulfur to a-C linked peptides (thuricins) and lasso peptides (microcin J25). A key objective is understanding interactions of such peptides with lipids and receptors as well as resulting membrane pore structures that lead to bacterial cell death. Targets include lipopeptides (tridecaptins) & cyclic bacteriocins (carnocyclin A). The bacterial species producing carnocyclin A (MicocinTM) has been approved for use in food for preservation of meat in USA and Canada, and has great potential as a therapeutic agent for infections resistant to conventional antibiotics. In terms of background, polyketides are secondary metabolites constructed by large (>200 kDa) enzymes (proteins) known as polyketide synthases (PKS) whose operation resembles fatty acid synthases. More than 20 important drugs are derived from known polyketides. Ultimately their function is to polymerize acetate, propionate or other small precursors into chains having specific length, functionality & stereochemistry. Our goals are to elucidate the mechanisms of highly reducing fungal PKS enzymes, which are remarkable molecular machines. The targets include enzymes that assemble lovastatin (a cholesterol-lowering drug and precusor to simvastatin (Zocor)), equisetin (inhibits HIV), dehydrocurvularin (an immunomodulator phytotoxin), cytochalasin E (an anti-angiogenesis anticancer agent) and hypothemycin (a kinase inhibitor & anticancer candidate).