Molecular mechanism of streptococcal adaptation to host nutritional defenses

化脓性链球菌（Streptococcus pyogenes，GAS）是一种主要的人类致病菌 导致严重的发病率和死亡率。GAS感染可导致多种疾病 包括风湿性心脏病（RHD），儿童获得性心脏病的主要原因。 在全球范围内，至少有3400万人患有RHD，每年造成345，000人死亡。因此 人GAS疫苗的开发仍然是医疗保健的优先事项。一个广泛的保护 由于候选疫苗的抗原变异，获得许可的GAS疫苗仍然难以捉摸。 不同的GAS血清型，病原体的遗传多样性，以及抗体的交叉反应性 GAS抗原与人体组织。为了克服这些挑战，保护公众健康， 因此，确定新的疫苗靶点和/或开发新的疫苗接种策略至关重要， 对GAS疾病产生广泛而有效的保护。我们最近的研究表明， 高度保守的细菌金属获取系统是关键的毒力决定因子， 有效的疫苗靶点，能够赋予针对GAS疾病的交叉血清型保护。的 金属输入者在感染期间与宿主营养免疫机制竞争获得金属 并促进细菌在敌对宿主环境中的存活。宿主展开营养免疫 作为先天免疫的组成部分，通过营养剥夺来延缓微生物生长的机制。 GAS感染的宿主富含宿主因子钙卫蛋白（CP），其从宿主细胞中螯合Zn。 殖民表面，以限制气体的增长。然而，GAS经受住了CP的冲击， 通过采用高亲和力Zn导入剂AdcABC在宿主中复制。这个模型的一个主要警告是 在GAS和其他革兰氏阳性细菌中，细胞膜结合的AdcABC样输入者 埋在厚厚的细胞壁层之下。AdcABC的掩蔽的亚细胞定位不能 解释其作为竞争性锌吸收机制对抗有效宿主营养防御的功能 以及它作为疫苗靶点的功效。本提案的主要目的是确定 GAS使用AdcA逃避宿主营养防御的机制，并评估新的AdcA- 基于疫苗接种策略，其对类人GAS感染的保护功效。使用 多学科的方法，我们将测试这一建议的核心假设，即气体使用非- 复制，无细胞膜囊泡（MV）与AdcABC包被的锌收购和颠覆CP- 介导的Zn限制。在完成拟议的研究，MV介导的机制基础， 将描述GAS Zn获取，并将描述基于蛋白质和MV的AdcA的保护功效。 将评估预防GAS疾病的疫苗接种。

Streptococcus pyogenes, also known as group A streptococcus (GAS), is a major human pathogen that causes significant morbidity and mortality. GAS infections can lead to several disease conditions including rheumatic heart disease (RHD), the major cause of acquired heart disease in children. Globally, at least 34 million people living with RHD causing 345,000 deaths per year. Thus, the development of a human GAS vaccine remains a healthcare priority. However, a broadly protective licensed GAS vaccine remains elusive due to the antigenic variation in vaccine candidates among different GAS serotypes, genetic diversity of the pathogen, and cross-reactivity of antibodies against GAS antigens with human tissues. To overcome these challenges and protect public health from GAS diseases, it is critical to identify novel vaccine targets and/or develop new vaccination strategies that produce broad and effective protection against GAS diseases. Our recent studies demonstrated that the highly conserved bacterial metal acquisition systems are critical virulence determinants and effective vaccine targets capable of conferring cross-serotypic protection against GAS diseases. The metal importers compete with host nutritional immune mechanisms to acquire metals during infection and promote bacterial survival in hostile host environments. Host deploys nutritional immune mechanisms, as components of innate immunity, to retard microbial growth by nutrient deprivation. GAS infected abscesses are enriched with host factor, calprotectin (CP), which sequesters Zn from the colonization surfaces to limit GAS growth. However, GAS withstands CP onslaught and successfully replicates in the host by employing the high-affinity Zn importer, AdcABC. A major caveat to this model is that, in GAS and other gram-positive bacteria, the cell membrane-bound AdcABC-like importers are buried underneath the thick cell wall layer. The masked subcellular localization of AdcABC fails to explain its function as a competitive Zn uptake mechanism against the efficient host nutritional defenses and its efficacy as a vaccine target. The primary objective of this proposal is to determine the mechanisms by which GAS uses AdcA to evade host nutritional defenses, and evaluate novel AdcA- based vaccination strategies for its protective efficacy against human-like GAS infections. Using a multidisciplinary approach, we will test the central hypothesis of this proposal that GAS uses non- replicating, cell-free membrane vesicles (MV) coated with AdcABC for Zn acquisition and subverts CP- mediated Zn limitation. At the completion of the proposed study, the mechanistic basis for MV-mediated GAS Zn acquisition will be delineated and protective efficacy of protein- and MV-based AdcA vaccination for GAS disease prevention will be assessed.