Structural and Functional Study of Influenza Virus Hemagglutinin

描述（由申请方提供）：由于自然进化的毒株及其可能被恐怖分子用作人造生物武器，由流感B病毒引起的感染仍然是对全球医疗保健的严重威胁。血凝素（HA）是一种主要的表面糖蛋白，参与流感感染的四个方面：（a）。HA是中和感染性的抗体的靶标;（B）. HA经历抗原漂移以逃避中和;（c）. HA与细胞表面受体唾液酸结合以引发感染;和（d）. HA介导病毒和靶膜的融合以允许病毒进入。人们现在对甲型流感病毒HA（AHA）的结构和功能有了广泛的了解，这是通过了解近30年前解决的H3亚型的结构而大大促进的。与此形成鲜明对比的是，人们对B型流感病毒HA（BHA）的了解甚少，特别是在抗体中和、抗原漂移和受体结合方面，这些与AHA有显著差异。该团队最近确定了来自流感B/香港/8/73毒株（B/HK HA）的BHA的第一个结构，该结构处于未配体状态以及与人类和禽类受体类似物的复合物。这些结构为解决该提案中的B型流感病毒的三个最关键问题提供了坚实的基础：精确的抗原结构、低受体结合亲和力和抗原漂移对BHA受体结合的影响。总体假设是BHA和AHA之间的结构差异决定了它们之间的功能差异，这些差异通过多样化的正选择性压力进一步调节。具体目标是：（1）.在BHA中定义一个新的抗原位点。对BHA抗原结构的更准确定义将大大增强人们对宿主-病原体关系的理解。（二）.确定BHA受体结合亲和力的分子决定因素。这一结果不仅有助于揭示受体结合亲和力的分子决定因素，而且有助于未来合理设计高亲和力受体类似物，从而有效地阻断流感B病毒与宿主受体的结合，从而降低流感B病毒引起的感染的严重性。（三）、表征受体结合位点的天然取代对BHA抗原性和受体结合的影响。这一目标的结果将为它们的影响提供原子基础，并阐明BHA在抗原漂移期间可以耐受的受体结合的变化程度。该团队最近在解决BHA第一组结构方面的成就使其成为唯一有资格进行拟议研究的团队。这些研究的结果将大大提高人们对B型流感病毒作为重要人类病原体的基本认识，可能有助于未来开发对抗由B型流感病毒感染引起的发病率和死亡率的新策略，并为B型流感病毒学领域提供强大的推动力。公共卫生相关性：流感病毒是国家过敏和传染病研究所C类优先病原体之一。由B型流感病毒引起的感染仍然是对全球医疗保健的严重威胁。拟议的研究旨在实质性地提高对流感B病毒作为重要人类病原体的基本认识，可能有助于未来开发对抗流感B病毒感染引起的发病率和死亡率的新策略，并为流感B病毒学领域提供强大的推动力。

DESCRIPTION (provided by applicant): Infection caused by influenza B virus remains a serious threat to global healthcare, due to naturally evolving strains and to their potential use as manmade bio-weapons by terrorists. Hemagglutinin (HA) is a major surface glycoprotein involved in four aspects of influenza infection: (a). HA is the target of antibodies for neutralization of infectivity; (b). HA undergoes antigenic drift to escape neutralization; (c). HA binds to cell-surface receptors, sialic acid, to initiate the infection; and (d). HA mediates fusion of viral and target membranes to allow viral entry. One now has extensive knowledge on structure and function of influenza A virus HA (AHA) that was greatly facilitated by knowing the structure of H3 subtype that was solved almost 30 years ago. In marked contrast, influenza B virus HA (BHA) is poorly understood, particularly on antibody neutralization, antigenic drift and receptor binding that differ significantly from those of AHAs. This team has most recently determined the first structures of BHA from influenza B/HongKong/8/73 strain (B/HK HA) in unliganded state as well as in complex with human and avian receptor analogs. These structures have provided a solid foundation to address the three most critical issues of influenza B virus in this proposal: the precise antigenic structure, the low receptor-binding affinity, and the impact of antigenic drift on receptor binding of BHA. The overall hypothesis is that the structural differences between BHA and AHA dictate the functional differences between them, which are further modulated by diversifying positive selective pressure. The specific aims are: (1). Define a new antigenic site in BHA. A more accurate definition of the antigenic structure of BHA will substantially enhance one's understanding of the host-pathogen relationship. (2). Determine the molecular determinants for BHA receptor-binding affinity. The results of this aim will not only reveal the molecular determinants for the receptor-binding affinity, but also may help future rational design of high-affinity receptor analogs that can efficiently block influenza B virus from attaching to host receptors, thus reducing the severity of influenza B virus caused infection. (3). Characterize the impact of natural substitutions at receptor-binding site on BHA antigenicity and receptor binding. The results of this aim will provide an atomic basis for their impacts, and elucidate the degree of variations in receptor binding that BHA can tolerate during antigenic drift. The recent accomplishment of this team in solving the first set of structures of BHA makes it uniquely qualified for the proposed studies. The results from these studies will substantially improve one's fundamental understanding of influenza B virus as an important human pathogen, may help future development of novel strategies for combating morbidity and mortality caused by influenza B virus infection, and provide a strong driving force to the influenza B virology field. PUBLIC HEALTH RELEVANCE: Influenza virus is among the National Institute of Allergy and Infectious Diseases Category C priority pathogens. Infection caused by influenza B virus remains a serious threat to global healthcare. The proposed studies aim to substantially improve the fundamental understanding of influenza B virus as an important human pathogen, may help future development of novel strategies for combating morbidity and mortality caused by influenza B virus infection, and provide a strong driving force to the influenza B virology field.