Molecular Targets in Peptidoglycan Synthesis

β -内酰胺类抗生素是治疗细菌性疾病的重要药物，其靶向的是交联肽聚糖链的必需转肽酶（青霉素结合蛋白或PBPs）。不幸的是，耐抗生素致病菌的出现是一个日益严重的问题，有可能使这些抗生素和其他抗生素过时。由于淋病奈瑟菌耐药菌株的出现，青霉素和四环素不再用于治疗淋球菌感染。此外，对氟喹诺酮类药物和第三代头孢菌素（目前推荐用于治疗淋病的两类抗生素）的耐药性正在增加。显然，迫切需要开发新的抗菌剂，既针对已知的分子靶标，如PBPs，也针对新的靶标，如催化聚糖链聚合的转糖基酶（TGases），以及在生物合成过程中分解肽聚糖的自溶酶。然而，由于缺乏这些酶的机制信息，新抗生素的开发一直受到阻碍。在这一建议，我们描述遗传，生化和结构研究三类酶参与肽聚糖代谢淋病奈瑟菌。每一个都被选择来解决以下一个或多个目标：(a)了解肽聚糖合成的生物学，(b)探索它们与抗生素的相互作用，(c)阐明抗生素耐药性的分子基础，(d)检查它们作为药物开发靶点的潜力。对头孢曲松中等水平耐药淋病奈瑟菌PBP 2的独特变异进行结构和生化研究，以探讨抗生素耐药的分子基础。作为参与细胞分裂的多酶复合体的一部分，裂解性TGase MltA的作用将通过遗传学研究进行研究。酰胺酶作为抗菌剂新靶点的适用性将从遗传学和晶体结构两方面进行研究。最后，TGase结构域的晶体结构将揭示这些酶的催化机制，为药物设计铺平道路。总之，这些研究将深入了解这些蛋白质在肽聚糖代谢中的功能作用，以及支持当前针对致病菌的抗菌剂所需的基本分子信息。

Beta-lactam antibiotics, which target the essential transpeptidases (penicillin-binding proteins or PBPs) that cross-link peptidoglycan strands, are important drugs in the treatment of bacterial diseases. Unfortunately, the emergence of antibiotic-resistant pathogenic bacteria is a growing problem and threatens to make these and other antibiotics obsolete. Penicillin and tetracycline are no longer used to treat gonococcal infections due to the emergence of resistant strains of N. gonorrhoeae. Moreover, resistance to fluoroquinolones and third-generation cephalosporins, the two classes of antibiotics current recommended in the treatment of gonorrhea, is increasing. Clearly there is an urgent need to develop new antimicrobials directed both against well-known molecular targets, such as PBPs, but also against novel targets such as transglycosylases (TGases), which catalyze the polymerization of glycan stands, and autolysins, which break down peptidoglycan during biosynthesis. Development of new antibiotics, however, has been hindered by a dearth of mechanistic information for these enzymes. In this proposal we describe genetic, biochemical and structural studies of three classes of enzyme involved in peptidoglycan metabolism in N. gonorrhoeae. Each has been selected to address one or more of the following aims: (a) to understand the biology of peptidoglycan synthesis, (b) to explore their interactions with antibiotics, (c) to elucidate the molecular basis for antibiotic resistance and (d) to examine their potential as targets for drug development. The molecular basis for antibiotic resistance will be investigated by structural and biochemical studies of a unique variant of PBP 2 from strains of N. gonorrhoeae with intermediate-level resistance to ceftriaxone. The role of the lytic TGase MltA as part of a multienzyme complex involved in cell division will be investigated by genetic studies. The suitability of the amidase AmiC as a novel target for antimicrobials will be examined both genetically and by solving its crystal structure. Finally, the crystal structure of a TGase domain will reveal the catalytic mechanism of these enzymes and pave the way for drug design. Together, these studies will provide insight into the functional roles of these proteins in peptidoglycan metabolism but also the essential molecular information needed to bolster the current repertoire of antimicrobials directed against pathogenic bacteria. The sexually transmitted disease gonorrhea is a growing public-health problem due to the emergence of strains harboring resistance to antibiotics such as penicillin. The development of new treatments for gonococcal disease requires detailed, three-dimensional pictures of essential proteins in these bacteria for use in drug discovery. This project will use X-ray crystallography to provide such information for a number of key proteins in N. gonorrhoeae that are involved in cell wall synthesis.