Resistance to antibiotics is a serious concern to treat infectious diseases and also, for food preservation. Existing antibiotics generally inhibit enzymes participating in key bacterial processes, such as formation of cell wall, replication, transcription and translation. However, bacteria have rapidly evolved new mechanisms to combat these antibiotics and it hence becomes indispensable to identify newer targets and identify/design inhibitors against them. Another concern is that most antibiotics are broad spectrum; they largely bind and inhibit the active site of the target enzyme. Rel proteins, which synthesize (and hydrolyze) (p)ppGpp in response to a variety of stress encountered by bacteria, is a profitable target owing to its distinct absence in humans and an intricate regulation of the catalytic activities. Inactivation of (p)ppGpp synthesis by Rel, disables bacterial survival in Mycobacterium tuberculosis and Staphylococcus aureus, while inactivating the hydrolysis activity was lethal. The poor MIC values of the currently known Rel inhibitors present a distinct opportunity to develop better inhibitors and warrants a detailed structural characterization and understanding of the complex regulation in Rel proteins. It will open new avenues for the design of effective, species-specific inhibitors. In an attempt to identify unique sites for inhibitor design using structure-based approaches, we initiate a study of Rel homologues from four different pathogenic bacteria, in order to compare their attributes with well characterized Rel homologues. Here, we present cloning, over-expression, purification and preliminary characterization of these four homologues; and suggest similarities and differences that can be exploited for inhibitor design.

对抗生素的抗药性是治疗传染病以及食品保存的严重问题。现有的抗生素通常抑制酶参与关键的细菌过程，例如细胞壁的形成，复制，转录和翻译。但是，细菌已迅速发展出与这些抗生素作斗争的新机制，因此，鉴定新的靶标并鉴定/设计针对它们的抑制剂变得必不可少。另一个问题是大多数抗生素的应用范围很广。它们很大程度上结合并抑制了靶酶的活性位点。相对于细菌遇到的各种压力，Rel蛋白可以合成（和水解）（p）ppGpp，由于其在人体中的独特存在和对催化活性的复杂调节，Rel蛋白是一种可盈利的靶标。结核分枝杆菌和金黄色葡萄球菌的失活水解活性是致命的。目前已知的Rel抑制剂的MIC值较低，这为开发更好的抑制剂提供了独特的机会，并且需要详细的结构表征和对Rel蛋白中复杂调控的理解。它将为设计有效的物种特异性抑制剂开辟新途径。为了尝试使用基于结构的方法识别抑制剂设计的独特位点，我们启动了对四种不同致病细菌的Rel同源物的研究，以便将其属性与特征明确的Rel同源物进行比较。在这里，我们介绍这四个同系物的克隆，过表达，纯化和初步表征。并提出可用于抑制剂设计的异同。