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Li-Lin Du’s laboratory reveals the molecular mechanism behind the toxin-antidote duality of wtf killer meiotic drivers
On December 14, 2023, Dr. Li-Lin Du’s laboratory published a research paper titled "Ubiquitination-mediated Golgi-to-endosome sorting determines the toxin-antidote duality of fission yeast wtf meiotic drivers" in Nature Communications. In this study, the authors discovered that the toxin-antidote duality of the selfish killer genes of the wtf gene family is determined by subcellular relocalization mediated by ubiquitination. This finding deepens the understanding of the molecular mechanism of selfish killer genes.
Mendel's law of segregation states that in a diploid organism, two alleles at a gene locus have an equal chance of being transmitted to offspring. However, a class of selfish genes called killer meiotic drivers (KMDs) violates this law. A selfish gene belonging to KMDs can kill gametes not inheriting it, resulting in its presence in more than 50% of the offspring. Although KMDs have been widely discovered in animals, plants, and fungi, the understanding of their molecular mechanisms is currently limited.
Previously, Li-Lin Du’s laboratory identified two KMDs, known as cw9 and cw27, through the study of intraspecific reproductive isolation in the fission yeast Schizosaccharomyces pombe. They both belong to the wtf gene family, encoding multi-pass transmembrane proteins. The selfish killer genes of the wtf gene family generate a short protein product and a long protein product through alternative transcription initiation. The short product is a toxin that can harm gametes, while the long product is an antidote that protects gametes inheriting the killer gene from harm. Under the combined action of the toxin and the antidote, only gametes not inheriting the killer gene are harmed. The antidote differs from the toxin by approximately 50 additional N-terminal amino acids. Understanding how this antidote-specific region leads to the difference between antidote and toxin is a key question in understanding the molecular mechanism of the wtf killer genes.
Through affinity purification combined with mass spectrometry analysis, the authors found that the N-terminal region of the antidote of cw9 (Cw9a) can bind to ubiquitin ligases belonging to the Rsp5/NEDD4 family. This interaction is mediated by the PY motifs (Leu/Pro-Pro-X-Tyr) on the N-terminal sequence of Cw9a. Mutating the PY motifs can convert the antidote from non-toxic to toxic. Conversely, fusing an artificial PY motif (artPY) to the toxin of cw9 (Cw9t) can convert the toxin from toxic to non-toxic. These results indicate that the function of the antidote-specific region is to recruit the Rsp5/NEDD4 family ubiquitin ligase. Furthermore, the authors found that there are 7 lysines in the N-terminal region of the antidote that can be modified by Rsp5/NEDD4 family ubiquitin ligases. Mutating these lysines to arginines converts the antidote from non-toxic to toxic. This suggests that ubiquitination inhibits the inherent toxicity of the antidote.
How does ubiquitination inhibit toxicity? The authors found that ubiquitination serves as a sorting signal to determine the subcellular localization of the antidote. Ubiquitinated antidote is transported from the trans-Golgi network (TGN) to the endosome and then to the vacuole. The antidote protein localized in vacuoles or endosomes do not exhibit toxicity. Conversely, when the PY motifs are mutated, the antidote is no longer ubiquitinated and is no longer transported from the TGN to the endosome, resulting in a subcellular localization similar to that of the toxin and causing the inherent toxicity of the antidote to manifest (Figure 1).
Figure 1. Ubiquitination-mediated subcellular relocalization determines the toxin-antidote duality.
How does the ubiquitinated antidote neutralize the toxicity of the toxin? The authors found that the antidote can interact with the toxin and the ubiquitination occurring on the antidote facilitates the transport of the antidote-toxin complex from the trans-Golgi network to the endosome, thereby causing a detoxifying effect.
The wtf gene family is believed to have originated more than a hundred million years ago. The authors discovered that the mechanism of neutralizing toxicity through ubiquitination is not only prevalent in the wtf family genes of Schizosaccharomyces pombe, but also present in the wtf family genes of Schizosaccharomyces octosporus, a species separated from S. pombe about a hundred million years ago, indicating that this is an ancient mechanism that may have appeared in the earliest stages of the wtf gene family's evolution.
Jin-Xin Zheng is the first author of this paper. Li-Lin Du is the corresponding author. Other contributors include Tong-Yang Du, Guang-Can Shao, Zhu-Hui Ma, Zhao-Di Jiang, Wen Hu, Fang Suo, Wanzhong He, and Meng-Qiu Dong. This work was supported by the Chinese Ministry of Science and Technology and the Beijing municipal government.
Link to the paper:
