Rajamanickam, R. R. | Search bioRxiv

bioRxiv2025

Human endogenous retrovirus K (HERV-K) envelope structures in pre- and post-fusion by Cryo-EM

The HERV-K envelope glycoprotein (Env) is aberrantly expressed in diseases including cancers and autoimmune disorders and is targeted by antibodies. The lack of structural information has hindered functional and immune recognition studies. We solved structures of the HERV-K Env in both pre- and post-fusion states with novel monoclonal antibodies using cryo-EM. The pre-fusion Env assembles as a trimer with a distinct fold and architecture compared to other retroviruses, while the post-fusion conformation features a unique "tether" helix within the TM subunit. A panel of monoclonal antibodies, elicited to facilitate structure determination, have been characterized for conformational and subunit specificity, serving as valuable research tools. These findings establish a structural framework for mechanistic studies of HERV-K Env in diseases and evaluation as a potential therapeutic target.

biochemistry↗

bioRxiv2023

Structure of a SARS-CoV-2 spike S2 subunit in a pre-fusion, open conformation

The 800 million human infections with SARS-CoV-2 and the likely emergence of new variants and additional coronaviruses necessitate a better understanding of the essential spike glycoprotein and the development of immunogens that foster broader and more durable immunity. The S2 fusion subunit is more conserved in sequence, is essential to function, and would be a desirable immunogen to boost broadly reactive antibodies. It is, however, unstable in structure and in its wild-type form, cannot be expressed alone without irreversible collapse into a six-helix bundle. In addition to the irreversible conformational changes of fusion, biophysical measurements indicate that spike also undergoes a reversible breathing action. However, spike in an open, "breathing" conformation has not yet been visualized at high resolution. Here we describe an S2-only antigen, engineered to remain in its relevant, pre-fusion viral surface conformation in the absence of S1. We also describe a panel of natural human antibodies specific for S2 from vaccinated and convalescent individuals. One of these mAbs, from a convalescent individual, afforded a high-resolution cryo-EM structure of the prefusion S2. The structure reveals a complex captured in an "open" conformation with greater stabilizing intermolecular interactions at the base and a repositioned fusion peptide. Together, this work provides an antigen for advancement of next-generation "booster" immunogens and illuminates the likely breathing adjustments of the coronavirus spike.

microbiology↗