Structural and Functional Study of Influenza Virus Hemagglutinin

描述（由申请人提供）：B型流感病毒引起的感染仍然是对全球卫生保健的严重威胁，这是由于其自然进化的毒株以及它们可能被恐怖分子用作人造生物武器。血凝素（HA）是一种主要的表面糖蛋白，与流感感染的四个方面有关：(a)。血凝素是抗体中和感染性的靶标；(b)。透明质酸经历抗原漂移以逃避中和；(c)。透明质酸与细胞表面受体唾液酸结合，引发感染；和(d)。透明质酸介导病毒和靶膜的融合，使病毒进入。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，这是由于了解了近30年前解决的H3亚型的结构而大大促进的。与之形成鲜明对比的是，人们对乙型流感病毒HA （BHA）了解甚少，特别是在抗体中和、抗原漂移和受体结合方面，这与甲型流感病毒HA有很大的不同。该团队最近首次从乙型流感/香港/8/73株（B/HK HA）中确定了非配体状态的BHA结构，以及与人类和鸟类受体类似物的复合物。这些结构为解决乙型流感病毒的三个最关键的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。总的假设是，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压力进一步调节。具体目标是：(1)。在底部钻具组合中定义一个新的抗原位点。更准确地定义BHA的抗原结构将大大提高人们对宿主-病原体关系的理解。(2）. 确定BHA受体结合亲和力的分子决定因素。本研究结果不仅揭示了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，有效阻断乙型流感病毒对宿主受体的附着，从而降低乙型流感病毒引起的感染的严重程度。(3)。表征受体结合位点的自然取代对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在抗原漂移过程中可以耐受的受体结合变化程度。该团队最近在解决BHA的第一组结构方面取得的成就使其具有独特的资格进行拟议的研究。这些研究结果将大大提高人们对乙型流感病毒作为一种重要的人类病原体的基本认识，可能有助于未来制定新的策略来对抗乙型流感病毒感染引起的发病率和死亡率，并为乙型流感病毒学领域提供强大的推动力。公共卫生相关性：流感病毒属于国家过敏和传染病研究所C类优先病原体。乙型流感病毒引起的感染仍然是对全球卫生保健的严重威胁。本研究旨在大大提高对乙型流感病毒作为重要人类病原体的基本认识，有助于未来制定新的策略来对抗乙型流感病毒感染引起的发病率和死亡率，并为乙型流感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.