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bioRxiv · 10.1101/2025.07.23.666482

Xenopus IgX informs engineering strategies of IgM and IgG hexamers

Zhang, R.·Ji, C.·Li, S.·Li, N.·Gao, N.·Xiao, J.
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Abstract

Polymeric immunoglobulins are essential components of the immune system in jawed vertebrates. While mammalian immunoglobulin M (IgM) typically forms a pentamer linked by the joining chain (J-chain), Xenopus laevis IgX assembles into a J-chain-independent polymer. Here, we present the cryo-electron microscopy (cryo-EM) structure of IgX, revealing its hexameric configuration. By incorporating the IgX tailpiece into human IgM, we achieved efficient IgM hexamer formation. Truncating IgMs natural tailpiece to a range of 11-16 residues also substantially enhanced hexamerization efficiency. Furthermore, introducing a shortened IgM tailpiece to IgG resulted in effective IgG hexamer formation. We further show that the engineered IgM and IgG hexamers targeting CD20 demonstrated robust complement-dependent cytotoxicity (CDC) against several B lymphoma cells. Additionally, the IgG-Fc hexamer functioned as a decoy, attenuating CDC in cell cultures. These findings deepen our understanding of polymeric immunoglobulin evolution and introduce innovative strategies for the development of IgM- and IgG-based biologics. One Sentence SummaryThe cryo-EM structure of the African clawed frog immunoglobulin IgX reveals a uniform hexameric assembly, inspiring innovative strategies for the development of therapeutic human IgM and IgG hexamers.

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Zhang, R., Ji, C., Li, S., Li, N., Gao, N., Xiao, J.. 2025-07-28. Xenopus IgX informs engineering strategies of IgM and IgG hexamers. https://doi.org/10.1101/2025.07.23.666482

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