Interaction of Aggregatibacter actinomycetemcomitans leukotoxin with membranes

描述(由申请人提供)：伴生放线杆菌是一种革兰氏阴性病原体，是局限性侵袭性牙周炎(LAP)和其他全身感染的病原体，包括感染性心内膜炎。LAP是一种疾病，在美国和世界各地都会影响医疗服务不足的儿童，其特征是支撑牙齿的牙周膜和牙槽骨结构崩溃。如果不进行干预，就会出现牙齿脱落，导致整容畸形和功能缺陷。伴生放线杆菌致病的方式尚未确定，但已知该细菌产生几种可能的毒力因子，包括重复毒素(RTX)家族的一种白毒素(Ltd.xA)。这种毒素会杀死人类的白细胞，并可能在机体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病的一种选择。LtxA对宿主细胞施加致死作用的机制涉及物理破坏的形成，如气孔。具体地说，毒素和膜的相互作用导致双层的弯曲，从而形成环状或脂质衬里的孔。这一论点的一个合乎逻辑的延伸将表明，LtxA因此与能够更容易弯曲或弯曲的脂类相互作用最强。这项拟议的研究旨在探索LtxA通过改变细胞膜结构来损伤细胞的能力。在第一个目标中，我们将研究脂曲率对膜相行为和孔道形成等膜变化的影响。在第二个目标中，将确定脂质曲率对LtxA结构的影响，并将研究这些结构变化与在目标1中观察到的膜变化之间的关系。最终的目的将是阐明LtxA诱导的毛孔的生物物理性质。这项研究将可以确定膜的物理性质，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.