Biology subjects

Saladin, B. A.

Publications and source records attributed to Saladin, B. A..

2 recordsLinked to original sources

bioRxiv2026

Structural basis for emetine inhibition of ribosome translocation in Toxoplasma gondii

Apicomplexan parasites, including Toxoplasma gondii and Plasmodium falciparum, are major human pathogens that cause toxoplasmosis and malaria, respectively. The existing structures of T. gondii translational machinery are from empty ribosomes that lack several key components, including ribosomal protein RACK1 (Receptor for Activated C Kinase 1). Here, we used cryo-electron microscopy (cryoEM) to determine high-resolution structures of T. gondii ribosomal complexes, including a translating 80S ribosome bound to mRNA and tRNA. These structures reveal that RACK1 occupies the conserved binding site on the 40S subunit observed in other eukaryotic ribosomes. We also determined the architecture of the ribosomal P-stalk and identified the ribosomal proteins uL10 and uL11, which were not observed in previous T. gondii ribosome structures. In addition, we determined structures of the 80S ribosome bound to mRNA, tRNA, and the translation inhibitor emetine in two distinct conformational states. These snapshots reveal two mechanisms by which emetine inhibits the translocation step of mRNA translation: either by dislodging the mRNA from the E-site of the ribosome or by acting as a molecular glue within the E-site, thereby stalling translocation. Together, these findings provide new insights into the molecular basis of protein synthesis in apicomplexan parasites and establish a structural framework for the development of future antiparasitic therapeutics. GRAPHICAL ABSTRACT O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=147 SRC="FIGDIR/small/740346v1_ufig1.gif" ALT="Figure 1"> View larger version (30K): org.highwire.dtl.DTLVardef@18b69d5org.highwire.dtl.DTLVardef@1d125e5org.highwire.dtl.DTLVardef@efc11org.highwire.dtl.DTLVardef@1c6d088_HPS_FORMAT_FIGEXP M_FIG C_FIG

molecular biology↗

bioRxiv2025

Human Pumilio proteins use fuzzy multivalent hydrophobic interactions to recruit the CCR4-NOT deadenylase complex to repress mRNAs

Pumilio (PUM) proteins are conserved RNA-binding proteins that control mRNAs involved in development, proliferation, and stem cell differentiation. Human PUM1 and PUM2 repress targets by recruiting the CCR4-NOT deadenylase complex through a metazoan-specific N-terminal repression domain (RD3), which is predicted to be intrinsically disordered. Here we dissect RD3 using cell-based reporter assays, protein interaction assays with recombinant proteins, and crosslinking mass spectrometry. We identify multiple short RD3 peptides that are sufficient for repression and bind directly to the C-terminal NOT module of CCR4-NOT, comprising CNOT1, CNOT2, and CNOT3 subunits. Crosslinking reveals numerous mutually exclusive contacts between RD3 and the NOT module, consistent with a multivalent "fuzzy" binding mode in which interactions are not defined by a single sequence or structure. Sequence scrambling shows that the linear amino acid order of RD3 is dispensable, whereas its physicochemical composition, in particular distributed aliphatic and aromatic residues, is essential for repression and CCR4-NOT binding. These findings support a model in which low-affinity, multivalent interactions between intrinsically disordered regions (IDRs) and effector complexes, governed by amino acid composition rather than precise sequence, underlie robust PUM-mediated repression, and exemplify general principles by which IDRs recruit the CCR4-NOT complex to regulate gene expression. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=74 SRC="FIGDIR/small/695197v1_ufig1.gif" ALT="Figure 1"> View larger version (18K): org.highwire.dtl.DTLVardef@d4680aorg.highwire.dtl.DTLVardef@fa9c3dorg.highwire.dtl.DTLVardef@12783f7org.highwire.dtl.DTLVardef@148e657_HPS_FORMAT_FIGEXP M_FIG Graphical Abstract C_FIG

molecular biology↗