Blaud, M. | Search bioRxiv

bioRxiv2026

Universally conserved isoasparylation sustains ribosome biogenesis and function

All living beings use ribosomes to synthesize proteins from -amino acids. Inherited from our common ancestor, a few universally conserved ribosome biogenesis steps, introducing essential ribosomal RNA modifications, have survived to our days. However, it was unknown whether similar primordial core mechanisms could also target ribosomal proteins. Here we show that the assembly and the function of ribosomes depend on the installation of an unusual {beta}-amino acid, isoaspartate, within the ribosomal protein uS11. In bacteria, mitochondria, and plastids, this modification is catalyzed by the metzincin-like hydrolase YbeY, whereas in archaea and eukaryotes, it is introduced by the atypical kinase Fap7. The formation of this strategically positioned isoaspartate enables correct maturation of the small ribosomal subunit to support protein synthesis and normal cell physiology.

biochemistry↗

bioRxiv2026

Dual-stage inhibition of Plasmodium falciparum by a Skeletocutis derived fungal metabolite targeting Pyruvate Kinase II

Plasmodium falciparum resistance to current first line treatments is threatening at-risk populations and underscores the urgent need for novel therapeutic targets and drugs. P. falciparum pyruvate kinases I and II are two essential enzymes with distinct roles and subcellular localizations within the parasite. PfPyrKI is cytosolic, while PfPyrKII is found in the apicoplast, a specific organelle of Apicomplexa, where it is required for the production of (d)NTPs essential for apicoplast maintenance. We identify skeletocutin E, a Basidiomycete-derived metabolite, as a specific inhibitor of PfPyrKII. Skeletocutin E inhibits in vitro the activity of PfPyrKII with an IC50 of 0.52 {+/-} 0.08 {micro}M through a mixed inhibition mechanism and does not affect the activities of three human pyruvate kinases. Structure-activity relationship analyses using synthetic skeletocutin E analogues allowed us to identify the molecular determinants of this inhibition. Furthermore, determination of the quaternary structure of PfPyrKII by mass photometry, showed that this enzyme exists as monomers, dimers, and tetramers in equal proportions, revealing its singularity compared to other pyruvate kinases. Interestingly, skeletocutin E does not alter the distribution of the complexes, indicating that it does not interact at the subunit interfaces. Importantly, skeletocutin E inhibits P. falciparum growth in both blood and liver stages, with IC values of 3.56 {+/-} 0.50 {micro}M in red blood cells and 3.70 {+/-} 0.74 {micro}M in primary human hepatocytes. Together, these findings establish PfPyrKII as a druggable antimalarial target and identify skeletocutin E as a promising lead compound for the rational development of dual-stage antimalarial therapies.

microbiology↗