Mechanisms of Polyketide, Amino Acid and Polypeptide Biosynthesis

拟议的化学生物学、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、蛋白质特性、酶抑制和蛋白质结构)中使用的方法的结合。它主要分为两个方面：一、细菌抗菌肽(氨基酸聚合物)的合成、构效关系和作用机制；二、真菌聚酮合成酶(PKS)的作用机制，它是真菌中的一种大蛋白，可以聚合醋酸形成生物活性分子，其中一些是重要的人类药物。就抗菌肽的背景而言，超过50%的医院感染是耐药的，相应的细菌病原体现在构成了严重的健康威胁。幸运的是，某些多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强几个数量级，可以杀死耐药病原体，并经常与目标细菌膜上的受体分子结合。它们可以是核糖体合成的(细菌素)，也可以是由非核糖体多肽合成酶产生的(例如脂肽)。一个中心主题是对这种多肽进行合成修饰，使其成为更简单、更容易获得的类似物，可用于人类摧毁耐药病原体。靶标包括抗生素(Nisin)、硫代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类和受体的相互作用，以及导致细菌细胞死亡的膜孔结构。靶标包括脂肽(十三肽)和环状细菌素(卡诺环素A)。产生卡诺环素A(MicocinTM)的细菌在美国和加拿大已被批准用于肉类保鲜食品，并具有巨大的潜力作为对常规抗生素耐药的感染的治疗剂。就背景而言，聚酮是由被称为聚酮合成酶(PKS)的大(200 KDa)酶(蛋白质)组成的次生代谢物，其操作类似于脂肪酸合成酶。20多种重要的药物都是从已知的聚酮类化合物中衍生出来的。归根结底，它们的功能是将醋酸酯、丙酸酯或其他小的前体聚合成具有特定长度、官能度和立体化学的链。我们的目标是阐明真菌PKS酶高度还原的机制，这是一种非凡的分子机器。这些靶点包括组装洛伐他汀(一种降胆固醇药物，辛伐他汀(Zocor)的前体)、木犀草素(抑制HIV)、脱氢曲霉素素(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)和次霉素(一种激酶抑制剂和抗癌候选药物)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).