Biologists: one-step closer to treatment for Crimean-Congo Hemorrhagic Fever

Work done in the lab of Prof. Jason McLellan at The University of Texas at Austin

About author

Akaash Mishra obtained a Bachelor and Master of Technology in Biotechnology from Jaypee Institute of Information Technology in India, where he worked on Chikungunya virus envelope protein interactions. He came to the U.S. in 2011 and earned an MS in Biochemistry and Molecular Biology from Indiana University, School of Medicine, where he targeted DNA-protein interactions of nucleotide excision repair proteins for cancer therapy. He then worked as an Associate Scientist at Cook Pharmica LLC for 2.5 years, focusing on biologics development. During his Ph.D. at the University of Texas, Austin, he has worked on structures of viral glycoproteins and their interactions with the host to aid in developing vaccines and antibody therapeutics.

University of Texas, Austin

Interview

How would you explain your research outcomes to the non-scientific community?

Crimean-Congo Hemorrhagic Fever (CCHF) is a terrible disease that is endemic in Asia, Africa, and Europe. It is caused by a tick-borne virus that specifically causes disease in humans and leads to death in up to 40% of the cases.

The CCHF virus relies on a shape-shifting molecule on its surface, called the Gc protein, to fuse with host cells. To effectively stop the virus from infecting a cell, a therapeutic agent needs to target the protein’s pre-fusion shape. Here we determined the structure of pre-fusion Gc protein bound to two neutralizing antibodies from recovered patients, as well as the structure of Gc in the post-fusion shape. By studying the pre-fusion and post-fusion shapes and locating where these antibodies bind, we determined that one antibody prevents the Gc protein from changing into the post-fusion shape, and the other prevents it from inserting part of itself into the membrane of a host cell. This explains why these two antibodies combined are so effective at blocking the virus from infecting cells.

In a previous study that we published earlier this year in the journal Cell, our consortium called Prometheus showed that these two antibodies potently neutralize the virus and prophylactically protect mice against a lethal virus challenge. Combining the virus-binding regions from the two antibodies produced a “bispecific antibody” that cleared the infection in sick mice and therapeutically protected them from dying. Currently, our group is working on developing this antibody further for use in human clinical trials.

Synergistic neutralization of Crimean-Congo Hemorrhagic Fever virus (CCHFV) by two monoclonal antibodies. Clockwise from the left panel: (1) Glycoproteins Gn (white) and Gc (in color) are anchored in the CCHFV envelope, coating the viral surface. CCHFV Gc is responsible for driving membrane fusion for virus entry, and Gn acts as a lock to avoid premature fusion activation of Gc. Upon virus entry into the host cell, the lock is released as Gn dissociates from Gc (2), which can then insert its “fusion loops” (orange end) into the cell membrane as an elongated trimer (3). Gc then adopts a hairpin-like conformation pulling its viral trans-membrane anchors (in grey) towards the fusion loops (4), thereby forcing viral and cellular membranes against each other to promote their fusion (5). Mishra and Hellert et al. describe the X-ray structure of trimeric post-fusion Gc (Top right panel) as well as the structure of pre-fusion monomeric Gc bound to the Fabs of two neutralizing antibodies (bottom right panel). Together, the structures show the two antibodies (6) act in concert to block membrane fusion: one inhibits membrane insertion by binding to the fusion loop, while the other prevents Gc trimer formation (7).

How do these findings contribute to your research area?

The research echoes a key approach that scientists, including The University of Texas at Austin’s Jason McLellan, have used in recent years to fight COVID-19 and RSV, signaling the emerging prominence of structural virology—the use of exquisitely detailed imaging of viral components to find their weaknesses—in preventing pandemics and curbing the infectious disease. Not many people heard about coronaviruses before COVID-19 pandemic. We need to be better prepared with such emerging viruses, which may not be causing an epidemic at this point in the U.S. but still have significant potential for future outbreaks. With structural virology, we are finding out the secrets of these proteins on the surface of viruses and their vulnerabilities—and that helps us build better therapeutics and vaccines.

What was the exciting moment during your research?

To obtain the structures presented in this report, we used X-ray crystallography. In X-ray crystallography, we grow crystals of a protein either by itself or in complex with other proteins. On passing, a beam of incident X-rays through the protein crystal, the X-rays are scattered/diffracted into many different directions that are detected by a detector. By analyzing the pattern of diffracted X-rays, structures of proteins/protein-complexes are determined. For an X-ray crystallographer, one of the most exciting moments is when their protein crystals diffract in a pattern such that they can obtain a high-resolution structure of their protein from it. This is what happened in this case, and I was very excited about it!

Also, determining the first structures of CCHFV fusion protein (a first in the whole family of related viruses) was very satisfying. Finally, analyzing the structures of the pre-fusion and post-fusion shapes together was the ultimate step of enlightenment as it revealed the mechanism of action of the neutralizing antibodies against CCHFV.

What do you hope to do next?

I have been working on research and development of biologics (vaccines and antibodies) and small molecule therapeutics for the past 10 years in different capacities across multiple institutions. I am looking forward to graduating with my Ph.D. in the spring of 2022 and utilizing my skill set at a biopharmaceutical company that is committed to treat, cure, , and prevent some of the most complex diseases of our time.

“With structural virology, we are finding out the secrets of these proteins on the surface of viruses and their vulnerabilities—and that helps us build better therapeutics and vaccines.”

Where do you seek scientific inspiration from?

I have been very fortunate to be a part of a lab that has played a significant role in the rapid development of the SARS-CoV2 vaccine. Watching the advances and breakthroughs, come together to help solve big problems such as a global pandemic in such a short span of time was very inspiring.

How do you intend to help Indian science improve?

I am an active member of STEMPeers community, a PhD career support group, a non-profit organization founded by Indian alumni. I plan to give back to the community by networking and mentoring young scientific minds in multiple ways to support their scientific journeys.

Reference

Akaash K. Mishra et al. Structural basis of synergistic neutralization of Crimean-Congo hemorrhagic fever virus by human antibodies. Science; 18 Nov 2021, First Release. DOI: 10.1126/science.abl6502

Edited by: Manveen K Sethi