Mechanisms of Mycoplasmal Disease Pathogenesis

描述（由申请人提供）：几乎所有细菌病原体的表面都包被有多糖（胞外多糖，EPS），可以保护细菌免受宿主防御，并调节细菌粘附于各种表面（包括宿主细胞和组织以及其他细菌）的能力。尽管电子显微照片显示许多菌种产生荚膜，一些菌种形成生物膜，细胞外基质中应该含有EPS，但支原体学领域在很大程度上忽略了多糖。支原体可引起包括人类在内的许多动物的慢性呼吸道、生殖器和关节炎疾病。支原体缺乏细胞壁似乎使其极易被宿主防御系统杀死，但即使在抗生素治疗的帮助下，这些生物体通常也难以从宿主体内根除。多糖可能是导致支原体感染慢性化的一个因素。我们的长期目标是以鼠病原体肺支原体为模式生物，阐明支原体的致病机制。有助于避免宿主防御的一个因素是支原体的Vsa（可变表面抗原）蛋白，其保护细胞免受补体裂解并调节对固体表面的粘附，从而调节生物膜形成。我们对生物膜的研究使我们最近认识到，尽管M.肺结核有几个基因被注释为在EPS合成中具有潜在作用。然而，M。肺炎链球菌产生至少两种EPS分子（EPS-I和EPS-II）。本建议的目标1是确定EPS-I和II的结构。结构的知识将有助于理解它们的合成机制以及它们如何与支原体蛋白和宿主分子相互作用的机制。目的2是通过分离和研究不产生EPS-Ⅰ或Ⅱ的突变株来研究EPS合成途径。有几个理由怀疑合成机制可能是全新的。一些数据表明，在该系统中，不需要核苷酸糖作为EPS合成的底物。已经鉴定了合成EPS-I或EPS-II所需的几个基因。这些基因编码被注释为ABC转运蛋白的蛋白质。然而，当含有这些基因中的两个的操纵子被克隆到其他种属的支原体中时，EPS-I被合成。因此，这些基因可能编码新的糖基转移酶，这些糖基转移酶仅在合成过程中输出不断增长的多糖链的意义上是转运蛋白。该系统中的合成机制可能很重要，并在其他支原体和可能的壁细菌中发现。目的3是研究每种EPS在发病机制中的作用。将不产生EPS-I或EPS-II的突变体与野生型支原体在小鼠中避免补体杀伤、细胞粘附、避免吞噬作用和引起疾病的能力进行比较。这些研究将导致控制支原体感染的新方法的开发，例如多糖的靶向或其合成的机制。

DESCRIPTION (provided by applicant): The surface of virtually all bacterial pathogens is coated with polysaccharides (exopolysaccharides, EPS) that can protect bacteria from host defenses and modulate the ability of the bacteria to adhere to various surfaces including host cells and tissue and other bacteria. The field of mycoplasmology has largely ignored polysaccharides although electron micrographs suggest that many species produce a capsule and some species form biofilms that should contain EPS in the extracellular matrix. Mycoplasmas cause chronic respiratory, genital and arthritic diseases in many animals including man. The lack of a cell wall might seem to make mycoplasmas highly susceptible to killing by host defenses, but these organisms are often difficult to eradicate from the host even with the help of antibiotic therapy. Polysaccharides may be a contributing factor to the chronicity of mycoplasmal infections. Our long-range goals are to unravel the pathogenic mechanisms of mycoplasmas, with the murine pathogen Mycoplasma pulmonis serving as a model organism. One factor that contributes to the avoidance of host defenses is the mycoplasma's Vsa (variable surface antigen) proteins that protect the cells from lysis by complement and modulate adherence to solid surfaces and thus biofilm formation. Our studies on biofilms led to the recent realization that polysaccharides are produced despite the fact that the complete genome sequence of M. pulmonis has few genes annotated as having a potential role in EPS synthesis. Nevertheless, M. pulmonis produces at least two EPS molecules (EPS-I and EPS-II). Aim 1 of this proposal is to determine the structure of EPS-I and II. Knowledge of the structures will be instrumental in understanding the mechanism of their synthesis and the mechanics of how they interact with mycoplasmal proteins and host molecules. Aim 2 is to study the pathway of EPS synthesis through the isolation and study of mutants that do not produce EPS-I or II. There are several reasons for suspecting that the mechanism for synthesis may be fundamentally novel. Some data suggest that nucleotide sugars are not needed as substrates for EPS synthesis in this system. Several of the genes that are required for synthesis of EPS-I or EPS-II have already been identified. These genes code for proteins that are annotated as ABC transporters. However, EPS-I is synthesized when an operon containing two of these genes are cloned into other species of mycoplasma. Thus, these genes may code for novel glycosyltransferases that are transporters only in the sense that they export the growing polysaccharide chain during synthesis. The synthesis machinery in this system will likely be important and found in other mycoplasmas and possibly walled bacteria. Aim 3 is to examine the role of each EPS in pathogenesis. Mutants that do not produce EPS-I or EPS-II will be compared to wild-type mycoplasmas for the ability to avoid killing by complement, cytadhere, avoid phagocytosis, and cause disease in mice. These studies will lead to the development of new approaches for the control of mycoplasmal infections, such as the targeting of the polysaccharides or the machinery for their synthesis.