Interaction of Aggregatibacter actinomycetemcomitans leukotoxin with membranes

描述（由申请人提供）：放线菌群是一种革兰氏阴性病原体，是局部侵袭性牙周炎（LAP）和其他全身性感染（包括感染性心内膜炎）的病因。LAP是一种影响美国和全世界医疗服务不足的儿童的疾病，其特征是牙周韧带和牙槽骨结构的破坏，这些结构可以固定牙齿。如果不进行干预，牙齿就会脱落，造成外观畸形和功能缺陷。放线菌引起疾病的方式尚未确定；然而，众所周知，这种细菌产生几种假定的毒力因子，包括一种白质毒素（LtxA），它是毒素重复序列（RTX）家族的成员。这种毒素杀死人类白细胞，并可能在生物在宿主中建立生态位期间逃避免疫反应的能力中发挥关键作用。因此，预防或干扰LtxA活性可能是成功治疗该疾病的一种选择。LtxA对宿主细胞施加致死作用的机制涉及形成物理破坏，如孔。具体来说，毒素和膜的相互作用导致双分子层弯曲，从而形成环状或脂质内衬孔。这一论点的逻辑延伸将表明，LtxA因此将与更容易弯曲或弯曲的脂质发生最强烈的相互作用。这项拟议的研究旨在探索LtxA通过改变细胞膜结构来破坏细胞的能力。在第一个目标中，脂质曲率对ltxa诱导的膜变化的影响，如相行为和孔形成，将被表征。在第二个目标中，将确定脂质曲率对LtxA结构的影响，并检查这些LtxA结构变化与aim 1中观察到的膜变化之间的关系。最终目的是阐明LtxA诱导孔隙的生物物理性质。这项研究将确定膜的物理性质，特别是曲率在ltxa诱导的膜破坏中的作用，并将建立这种破坏的机制。

DESCRIPTION (provided by applicant): Aggregatibacter actinomycetemcomitans is a gram negative pathogen that is the etiologic agent of localized aggressive periodontitis (LAP) and other systemic infections, including infective endocarditis. LAP, a disease which affects medically-underserved children in both the United States and throughout the world, is characterized by a breakdown of the periodontal ligament and alveolar bone structure that holds the teeth in place. Without intervention, loss of teeth occurs, causing both a cosmetic deformity and a functional defect. The manner by which A. actinomycetemcomitans causes disease has not been determined; however, it is known that the bacterium produces several putative virulence factors, including a leukotoxin (LtxA) that is a member of the repeats-in-toxin (RTX) family. This toxin kills human white blood cells and likely plays a key role in the ability of the organism to evade the immune response during its establishment of an ecological niche in the host. Thus, preventing or interfering with LtxA activity may be one option for successful treatment of the disease. The mechanism by which LtxA exerts its lethal effect on the host cell involves the formation of a physical disruption, such as a pore. Specifically, the interaction of the toxin and membrane results in a bending of the bilayer that leads to the formation of a toroidal, or lipid-lined, pore. A logical extension of this argument would suggest that LtxA will therefore interact most strongly with lipids that are able to bend or curve more easily. The proposed study is designed to explore the ability of LtxA to damage cells by altering the structure of their membranes. In the first aim, the effect of lipid curvature on LtxA-induced membrane changes, such as phase behavior and pore formation, will be characterized. In the second aim, the effect of lipid curvature on LtxA structure will be determined and the relation between those LtxA structural changes and the membrane changes observed in Aim 1 will be examined. The final aim will elucidate the biophysical properties of LtxA- induced pores. This study will allow determination of the role of the physical properties of the membrane, specifically curvature, on LtxA-induced membrane disruption, and will establish the mechanism of this disruption.