Host-mediated zinc sequestration during Acinetobacter baumannii infection

项目总结 鲍曼不动杆菌是一种重要的医院内病原体，可引起一系列疾病，包括 呼吸道和尿路感染、脑膜炎、心内膜炎、伤口感染和菌血症。事实上，A. 鲍曼氏杆菌现在占世界一些地区所有重症监护病房感染的20%， 肺炎是最常见的表现。鲍曼不动杆菌的临床意义被推进 这种细菌对几乎所有的抗生素迅速产生抗药性。新目标的识别 治疗干预对于我们保护公众健康免受这一新出现的传染病威胁的能力至关重要。 一个很有前途的治疗开发领域利用了所有细菌病原体都需要营养金属的想法 以引起感染。这种方法模拟了宿主介导的金属隔离，这是对 感染在一种称为“营养免疫”的过程中。矛盾的是，对金属的饮食限制加剧了 感染强调金属丰度的变化如何深刻地影响宿主-病原体的结局 互动。宿主蛋白钙保护素(CP)是免疫调节的重要分子之一 金属限制和CP通过包括锌(锌)在内的营养金属的螯合来保护人体免受感染。 利用CP作为探针，我们已经发现了鲍曼不动杆菌内一个对生存至关重要的遗传位点 在依赖CP的锌饥饿条件下。该基因座编码保守的COG0523的一个成员 Zur诱导的GTPase A家族，我们称之为Zur诱导的GTPase A(ZIGA)。我们还发现了第二个COG0523 鲍曼不动杆菌基因组中的一员，我们称之为0934。ZIGA和0934具有生物学特性 与将锌插入到客户蛋白中的金属配位配位酮一致。我们的初步数据显示0934和 ZIGA结合并调节参与细胞壁合成和再循环的客户金属酶。基于这些 最基本的发现，我们假设鲍曼不动杆菌在肺部的定植导致大量 CP的积累使鲍曼黑线姬松茸缺乏营养锌。我们进一步假设ZIGA和0934 调节锌饥饿期间的细胞壁重塑，以适应营养锌转运体插入到 细胞膜是对抗宿主或饮食造成的锌饥饿所必需的。 为了测试这个中心模型，我们提出了一系列实验，旨在了解这一机制和 鲍曼不动杆菌对膳食和寄主缺锌反应的病理生理后果 在肺炎期间。在这些研究中，我们将(I)定义ZIGA和0934与它们的分子相互作用 金属蛋白客户，(Ii)询问ZigA和0934在鲍曼不动杆菌中的生理功能，以及(Iii) 确定ZIGA和0934在肺炎发病机制中应对锌饥饿的重要性。 这项研究将为细菌如何对饮食或免疫调节的锌做出反应建立一个新的范式 通过金属配位体依赖的细胞壁内稳态调节来限制感染过程。

PROJECT SUMMARY Acinetobacter baumannii is an important nosocomial pathogen that causes a range of diseases, including respiratory and urinary tract infections, meningitis, endocarditis, wound infections, and bacteremia. In fact, A. baumannii is now responsible for up to 20% of all intensive care unit infections in some regions of the world with pneumonia being the most common presentation. The clinical significance of A. baumannii has been propelled by this organism’s rapid acquisition of resistance to virtually all antibiotics. The identification of novel targets for therapeutic intervention is critical to our ability to protect the public health from this emerging infectious threat. A promising area of therapeutic development exploits the idea that all bacterial pathogens require nutrient metal to cause infection. This approach mimics host-mediated metal sequestration, which is a potent defense against infection in a process termed “nutritional immunity”. Paradoxically, dietary restriction of metal exacerbates infection underscoring how alterations in metal abundance can profoundly impact the outcome of host-pathogen interactions. The host protein calprotectin (CP) is one of the most important contributors to immune-mediated metal restriction and CP protects against infection through the chelation of nutrient metals, including zinc (Zn). Using CP as a probe, we have uncovered a genetic locus within A. baumannii that is important for survival during conditions of CP-dependent Zn starvation. This locus encodes a member of the conserved COG0523 family of GTPases that we have named Zur-induced GTPase A (ZigA). We have also found a second COG0523 member within the A. baumannii genome that we refer to as 0934. ZigA and 0934 have biological properties consistent with metallochaperones that insert Zn into client proteins. Our preliminary data indicate that 0934 and ZigA bind and regulate client metalloenzymes involved in cell wall synthesis and recycling. Based on these fundamental discoveries, we hypothesize that A. baumannii colonization of the lung leads to massive accumulation of CP which starves A. baumannii for nutrient Zn. We further hypothesize that ZigA and 0934 regulate cell wall remodeling during Zn starvation to accommodate insertion of nutrient Zn transporters into the cell envelope that are necessary to combat host- or dietary-imposed Zn starvation. To test this central model, we propose a series of experiments aimed at understanding the mechanism and pathophysiological consequence of the A. baumannii response to dietary and host-imposed Zn deprivation during pneumonia. In these studies, we will (i) define the molecular interactions of ZigA and 0934 with their metalloprotein clients, (ii) interrogate the physiological function of ZigA and 0934 in A. baumannii, and (iii) determine the importance of ZigA and 0934 in response to Zn starvation during the pathogenesis of pneumonia. This research will establish a new paradigm for how bacteria respond to dietary- or immune-mediated Zn restriction during infection through metallochaperone-dependent regulation of cell wall homeostasis.