期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：2022
卷号：119
期号：6
DOI：10.1073/pnas.2115379119
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：Significance
Influenza hemagglutinin (HA) is a prototypical class I fusion protein and a major component of current flu vaccines. HA is a metastable glycoprotein and undergoes conformational changes to the so-called postfusion state. Stabilization of the prefusion conformations of fusion proteins has proven to be a key success factor for the induction of efficacious immune response and stabilization has become a grand challenge in structural vaccinology. The study shows that three stabilizing mutations in two important pH-sensitive switch regions involved in the early refolding process impede refolding of the prefusion HA. Based on the substitutions of these highly conserved and buried HA residues a generally applicable stabilization strategy for all subtypes of group 1 and 2 influenza A HA was developed.
For an efficacious vaccine immunogen, influenza hemagglutinin (HA) needs to maintain a stable quaternary structure, which is contrary to the inherently dynamic and metastable nature of class I fusion proteins. In this study, we stabilized HA with three substitutions within its pH-sensitive regions where the refolding starts. An X-ray structure reveals how these substitutions stabilize the intersubunit β-sheet in the base and form an interprotomeric aliphatic layer across the stem while the native prefusion HA fold is retained. The identification of the stabilizing substitutions increases our understanding of how the pH sensitivity is structurally accomplished in HA and possibly other pH-sensitive class I fusion proteins. Our stabilization approach in combination with the occasional back mutation of rare amino acids to consensus results in well-expressing stable trimeric HAs. This repair and stabilization approach, which proves broadly applicable to all tested influenza A HAs of group 1 and 2, will improve the developability of influenza vaccines based on different types of platforms and formats and can potentially improve efficacy.
