Molecular Mechanisms of msp2 Variation in Rickettsiae

描述（由申请方提供）：本提案的目的是提高我们对引起人类和动物埃立克体病和无形体病的蜱传立克次体病原体发病机制的理解。这些病原体有效地利用小的基因组（<1.5Mb）来逃避免疫应答并在哺乳动物储库宿主中建立持续感染，在蜱中肠和唾液腺中定殖和复制，并在蜱的重新进食后发展感染性以实现向前传播。MSP 2最初在边缘无浆体中被定义，并且用该病原体感染牛和蜱为发现用于修饰表面蛋白质组的机制提供了极好的模型。在前一个项目期间，我们确定了MSP 2和相关表面paradox MSP 3的单个表达位点的节段性基因转换，作为产生表面多样性的主要机制，并证明了哺乳动物宿主和蜱虫载体之间操纵子编码蛋白的差异表达。嗜吞噬细胞无形体使用类似的基因转换机制在人类患者中表达大量的外膜蛋白，其他人的研究支持从多个位点表达以产生表面多样性。分析了A.边缘基因组揭示了与msp 2相关的外膜蛋白基因的复杂家族。该msp 2超家族由32个旁系同源物组成，包括两个msp 2和msp 3操纵子连接的表达位点、单个msp 4基因位点、多个msp 2和msp 3假基因以及其他未表征的msp 2样旁系同源物。我们假设这些旁系同源物的差异表达和它们之间的重组在病原体表面产生多样性，并提供生物体适应和持续存在于不同宿主和细胞环境的能力。本研究的具体目标是：1）确定msp 2超家族基因在哺乳动物和无脊椎动物宿主感染过程中是否差异表达; 2）确定msp 2超家族基因簇内操纵子结构和多样性的产生; 3）确定msp 2超家族蛋白在哺乳动物和无脊椎动物宿主中差异调节的机制;和4]比较A. marginale和A.嗜吞噬细胞菌

DESCRIPTION (provided by applicant): The objective of this proposal is to improve our understanding of the mechanisms of pathogenesis of tick borne rickettsial pathogens that cause ehrlichiosis and anaplasmosis of humans and animals. These pathogens efficiently utilize a small genome (<1.5 Mb) to evade the immune response and establish persistent infection in the mammalian reservoir host, to colonize and replicate in the tick midgut and salivary glands, and to develop infectivity upon renewed feeding of the tick to effect onward transmission. MSP2 was initially defined in Anaplasma marginale and infections of cattle and ticks with this pathogen provide an excellent model for discovering the mechanisms used to modify the surface proteome. In the prior project period, we identified segmental gene conversion of single expression sites for MSP2, and a related surface paralogue MSP3, as a primary mechanism for generating surface diversity and demonstrated differential expression of operon-encoded proteins between the mammalian host and tick vector. A similar gene conversion mechanism is used by Anaplasma phagocytophilum to express a large repertoire of outer membrane proteins in human patients and studies by others support expression from multiple loci to generate surface diversity. Analysis of the A. marginale genome reveals a complex family of outer membrane protein genes related to msp2. This msp2 superfamily is comprised of 32 paralogues, comprising the two msp2 and msp3 operon-linked expression sites, a single msp4 gene locus, multiple msp2 and msp3 pseudogenes, and other uncharacterized msp2-like paralogues. We hypothesize that differential expression of these paralogues and recombination between them generates diversity in the pathogen surface and provides the ability of organisms to adapt to and persist in different hosts and cellular environments. The specific aims of the present proposal are: 1] Determine if msp2 superfamily genes are differentially expressed during infection of the mammalian and invertebrate hosts; 2] Determine the operon structure and generation of diversity within msp2 superfamily gene clusters; 3] Identify the mechanisms for differential regulation of the msp2 superfamily proteins in the mammalian and invertebrate hosts; and 4] Compare regulation of expression of msp2 superfamily proteins in A. marginale and A. phagocytophilum.