Boodwa-Ko, D. | bioRxiv Science

bioRxiv2025

Germline Targeted Baboon Apolipoprotein L-1 Protects Mice Against African Trypanosomes

Certain primates are immune to infection by most African trypanosome parasites due to apolipoprotein L-1 (APOL1), a primate-specific ion channel-forming protein. To broaden our understanding of primate APOL1, we generated a panel of trypanosome-resistant murine models expressing various primate APOL1 proteins. We used these mice to investigate the role of APOL1 in trypanosome immunity in vivo by challenging them with various human and livestock trypanosome isolates. Baboon APOL1 provides partial protection to trypanosome isolates, though its protective capacity was limited by poor expression. A more highly expressed chimeric APOL1 encoding human APOL1 with the baboon APOL1 C-terminus was protective against human-infective trypanosomes, although with a fitness cost likely associated with high expression. We investigated the long-standing assumption that human resistance to Trypanosoma vivax is mediated by APOL1. Surprisingly, APOL1-expressing mice were fully susceptible to T. vivax infection, challenging this hypothesis. These model systems are useful tools for evaluating the possibility of generating genetic engineered livestock for disease control.

microbiology↗

bioRxiv2025

Efficient packaging of HIV-1 genomes via recognition of its adenosine-rich content by a heterologous RNA-binding domain

The HIV-1 genome (gRNA) has an unusually biased nucleotide content and is rich in adenosines. Selective packaging of the gRNA is thought to be driven by specific binding of the nucleocapsid (NC) domain of the viral Gag protein to the packaging signal ({Psi}) in the host cell cytosol. However, deletion of regions within {Psi} reduces--but does not completely abolish--genome packaging. To probe whether another feature of the gRNA may contribute to the selective gRNA packaging process, we replaced NC with heterologous RNA-binding domains (RBDs) with distinct RNA-binding properties. Surprisingly, despite disparate RNA binding specificities, all Gag-RBD chimeras successfully recruited the gRNA to the plasma membrane, suggesting that the initial gRNA recognition in the cytosol is not rate limiting. Notwithstanding, many chimeras exhibiting G/C binding specificity were arrested at the assembly stage. Only the Gag-SRSF5 chimera, which multimerized efficiently on adenosine-rich sequences on the gRNA, assembled efficiently and packaged gRNA at near wild-type levels. Importantly, rationally designed mutations that altered the A/G-rich binding specificity of Gag-SRSF5 decreased genome encapsidation efficiency. Furthermore, many Gag chimeras displayed potent dominant negative activities, highlighting NC functions as a targetable step in virus replication. Together, our findings reveal an unexpected aspect of the HIV-1 gRNA, its biased nucleotide content, as a key driver of selective genome packaging. SIGNIFICANCEHow HIV-1 selectively packages its genome (gRNA) into virions is poorly understood. To probe this, we replaced the viral nucleocapsid (NC) protein with heterologous RNA-binding domains (RBDs) from cellular hnRNP and SR protein families. Remarkably, despite their distinct RNA-binding specificities, all Gag-RBD chimeras successfully recruited the gRNA to the plasma membrane, suggesting that the initial gRNA recognition is not rate limiting. Only the Gag-SRSF5 chimera packaged gRNA efficiently which correlated with its capacity to multimerize on adenosine-rich sequences on the gRNA. Notably, several Gag chimeras exhibited strong dominant negative effects, underscoring NC functions as a targetable step in virus replication. Together, these findings uncover that the biased nucleotide content of the HIV-1 gRNA facilitates its selective packaging into virus particles.

microbiology↗