Buder, K. | bioRxiv Science

bioRxiv2025

Structural Basis for OAS2 Regulation and its Antiviral Function

Oligoadenylate synthetase (OAS) proteins are immune sensors for double-stranded RNA and critical for restricting viruses. OAS2 comprises two OAS domains, only one of which can synthesize 2-5-oligoadenylates for RNase L activation. Existing structures of OAS1 provide a model for enzyme activation, but do not explain how multiple OAS domains discriminate RNA length. Here, we discover that OAS2 exists in an autoinhibited state as a zinc-mediated dimer and present a mechanism for RNA length discrimination: the catalytically deficient domain acts as a molecular ruler that prevents autoreactivity to short RNAs. We demonstrate that dimerization and myristoylation localize OAS2 to Golgi membranes and that this is required for OAS2 activation and restriction of viruses that exploit the endomembrane system for replication, e.g. coronaviruses. Finally, our results highlight the non-redundant role of OAS proteins and emphasize the clinical relevance of OAS2 by identifying a patient with a loss-of-function mutation leading to autoimmune disease.

biochemistry↗

bioRxiv2025

Disrupted Sphingosine-1-Phosphate Homeostasis Drives Nephrotoxicity in Sphingosine-1-Phosphate Lyase Insufficiency Syndrome (SPLIS)

Sphingosine-1-phosphate lyase insufficiency syndrome (SPLIS), also known as nephrotic syndrome type 14 (NPHS14), is an autosomal recessive disorder characterized by renal, neurological, dermatological, endocrine, and immunological symptoms. This condition is caused by loss-of-function mutations in the SGPL1 gene, which encodes sphingosine-1-phosphate lyase (SGPL1p/SPL), the enzyme responsible for the terminal degradation of sphingosine-1-phosphate (S1P) in sphingolipid catabolism. We investigated a novel case of SPLIS associated with a recently reported SGPL1 mutation (c.1084T>A; p.Ser362Thr). Using stable isotope flux analyses, we demonstrated in patient-derived fibroblasts and HEK293T SGPL1 knockout models that SGPL1p deficiency does not consistently result in pathological S1P accumulation. Instead, SPL-deficient cells are able to maintain steady-state S1P levels through two compensatory mechanisms: O_LIRegulation of de novo sphingolipid synthesis via the ORMDL-ceramide axis. C_LIO_LIIncreased conversion of excess ceramides into glycosphingolipids. C_LI However, when steady-state conditions are disrupted--either by external sphingolipid supplementation or by impairing homeostatic control--a pathological increase in intracellular S1P occurs in SPL-deficient cells. In vivo, Sgpl1-/-mice exhibited significant urinary excretion of S1P and marked S1P enrichment in the kidneys. This pathological accumulation of S1P dysregulates cytoskeletal homeostasis, impairing renal epithelial formation. Based on these findings, we hypothesize that the reabsorption of urinary S1P contributes to toxic renal accumulation, providing an explanation for the nephrotoxicity observed in SPLIS and its association with nephrotic syndrome. Importantly, we found that the cytoskeletal disruptions could be mitigated by inhibiting the Rho-ROCK signaling pathway using the clinically approved inhibitor Fasudil. These findings illuminate the pathophysiological basis of SPLIS nephrotoxicity and propose a promising pharmacological intervention strategy. Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=144 SRC="FIGDIR/small/634100v1_ufig1.gif" ALT="Figure 1"> View larger version (24K): org.highwire.dtl.DTLVardef@e70e68org.highwire.dtl.DTLVardef@1630198org.highwire.dtl.DTLVardef@fde277org.highwire.dtl.DTLVardef@1f2b8e_HPS_FORMAT_FIGEXP M_FIG C_FIG

physiology↗