AlphaFold reveals how pathogenic Leptospira use cross-kingdom thiol-disulfide exchange to evade the complement membrane attack complex

Authors: HINDS, ABBIE - University Of Liverpool; JOHNSON, EMILY - University Of Liverpool; STATON, GARETH - University Of Liverpool; NJUME, FERDINAND - University Of Liverpool; CROSBY-DURANNI, HAYLEY - University Of Liverpool; Nally, Jarlath; CARTER, STUART - University Of Liverpool; RIGDEN, DANIEL - University Of Liverpool; EVANS, NICHOLAS - University Of Liverpool

Submitted to: mBio
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/20/2026
Publication Date: 6/15/2026
Citation: Hinds, A., Johnson, E., Staton, G., Njume, F.N., Crosby-Duranni, H.E., Nally, J.E., Carter, S., Rigden, D.J., Evans, N.J. 2026. AlphaFold reveals how pathogenic Leptospira use cross-kingdom thiol-disulfide exchange to evade the complement membrane attack complex. mBio. https://doi.org/10.1128/mbio.00878-26.
DOI: https://doi.org/10.1128/mbio.00878-26

Interpretive Summary: Leptospirosis is a worldwide significant zoonotic disease that infects a wide range of mammals, including cattle and humans. The disease is caused by bacteria belonging to Leptospira – a genus encompassing two clades, pathogenic species (P) and saprophytic species (S) (free-living in the environment, not disease associated). Globally, it is estimated that one million cases of human leptospirosis occur per year, leading to 60,000 deaths. Both cattle and humans can suffer from acute disease, which causes flu-like symptoms and can lead to severe kidney damage and death. The innate immune system acts as the host’s first line of defense against invading leptospires, with the activation of the complement system occurring in the first few hours following infection, to attack leptospires and limit infection. However, pathogenic species of Leptospira have developed methods to overcome these attacks. In this study, we used the software AlphaFold2 to predict how the protein LIC13259 interacts with complement to limit its activity and validated these interactions experimentally. We discovered that LIC13259 of pathogenic, but not saprophytic, Leptospira binds specifically to the complement component C8' through thiol-disulphide exchange to enable evasion of the membrane attack complex. Complement-mediated killing assays confirmed that disrupting this interaction resulted in pathogenic Leptospira LIC13259 complement inhibition ability being abolished akin to that exhibited by saprophytic LIC13529. These results reveal an unprecedented intermolecular disulphide bond mediating cross-kingdom protein-protein interaction involved in immune evasion. This study furthers our interpretation of Leptospira host-pathogen interactions and illustrates the value of AlphaFold2 structure predictions in understanding pathogen biology.

Technical Abstract: Leptospirosis is a worldwide, severe infectious disease that affects a range of mammals. Leptospira are classified as pathogenic or saprophytic with serum resistance as a key differentiator. LIC13259 is a Leptospira surface lipoprotein involved in pathogenesis that binds to the host’s complement system. Using AlphaFold2 predictions and biochemical experimental validation, we discovered that LIC13259 of pathogenic, but not saprophytic, Leptospira binds specifically to C8' through thiol-disulphide exchange, reducing association with C8a and enabling evasion of the membrane attack complex. Complement-mediated killing assays confirmed that replacing disulphide bond-associated cysteine-133 with an alanine in LIC13259 resulted in pathogenic Leptospira LIC13259 complement inhibition ability being abolished akin to that exhibited by saprophytic LIC13529. These results reveal an unprecedented intermolecular disulphide bond mediating cross-kingdom protein-protein interaction involved in immune evasion. This study furthers our interpretation of Leptospira host-pathogen interactions and illustrates the value of AlphaFold2 structure predictions in understanding pathogen biology.