Biology subjects

Fargason, T. E.

Publications and source records attributed to Fargason, T. E..

3 recordsLinked to original sources

bioRxiv2024

Controlled by disorder: phosphorylation modulates SRSF1 domain availability for spliceosome maturation

Serine/arginine-rich splicing factor 1 (SRSF1) is key in the mRNA lifecycle including transcription, splicing, nonsense-mediated decay, and nuclear export. Consequently, its dysfunction is linked to cancers, viral evasion, and developmental disorders. The functionality of SRSF1 relies on its interactions with other proteins and RNA molecules. These processes are regulated by phosphorylation of its unstructured arginine/serine-rich tail (RS). Here, we characterize how phosphorylation affects SRSF1s protein and RNA interaction and phase separation. Using NMR paramagnetic relaxation enhancement and chemical shift perturbation, we find that when unphosphorylated, SRSF1s RS interacts with its first RNA-recognition motif (RRM1). Phosphorylation of RS decreases its interactions with RRM1 and increases its interactions with the RNA-binding site. This change in SRSF1s intramolecular interactions increases the availability of protein-interacting sites on RRM1 and weakens RNA binding of SRSF1. Phosphorylation alters the phase separation of SRSF1 by diminishing the role of arginine in intermolecular interactions. These findings provide an unprecedented view of how SRSF1 influences the early-stage spliceosome assembly. SUMMARYPhosphorylation of SRSF1 is pivotal in pre-mRNA processing and is dysregulated in various pathologies. Modeling of SRSF1 based on NMR restraints reveals phosphorylation alters the accessibility of protein-protein and protein-RNA interaction sites on SRSF1s RRM1 domain, altering its binding preferences

biochemistry↗

bioRxiv2023

Unearthing SRSF1's Novel Function in Binding and Unfolding of RNA G-Quadruplexes

SRSF1 governs splicing of over 1,500 mRNA transcripts. SRSF1 contains two RNA-recognition motifs (RRMs) and a C-terminal Arg/Ser-rich region (RS). It has been thought that SRSF1 RRMs exclusively recognize single-stranded exonic splicing enhancers, while RS lacks RNA-binding specificity. With our success in solving the insolubility problem of SRSF1, we can explore the unknown RNA-binding landscape of SRSF1. We find that SRSF1 RS prefers purine over pyrimidine. Moreover, SRSF1 binds to the G-quadruplex (GQ) from the ARPC2 mRNA, with both RRMs and RS being crucial. Our binding assays show that the traditional RNA-binding sites on the RRM tandem and the Arg in RS are responsible for GQ binding. Interestingly, our FRET and circular dichroism data reveal that SRSF1 unfolds the ARPC2 GQ, with RS leading unfolding and RRMs aiding. Our saturation transfer difference NMR results discover that Arg residues in SRSF1 RS interact with the guanine base but other nucleobases, underscoring the uniqueness of the Arg/guanine interaction. Our luciferase assays confirm that SRSF1 can alleviate the inhibitory effect of GQ on gene expression in the cell. Given the prevalence of RNA GQ and SR proteins, our findings unveil unexplored SR protein functions with broad implications in RNA splicing and translation.

biophysics↗

bioRxiv2022

Peptides Mimicking RS Repeats Modulate Phase Separation of SRSF1, Revealing a Reliance on Combined Stacking and Electrostatic Interactions

Phase separation plays crucial roles in both sustaining cellular function and perpetuating disease states. Despite extensive studies, our understanding of this process is hindered by low solubility of phase-separating proteins. One example of this is found in SR proteins. These proteins are characterized by domains rich in arginine and serine (RS domains), which are essential to alternative splicing, in vivo phase separation, and a low solubility that has made these proteins difficult to study for decades. Here, we solubilize the founding member of the SR family, SRSF1, by introducing a peptide mimicking RS repeats as a co-solute. We find that this RS-mimic peptide forms interactions similar to those of the proteins RS domain. Both interact with a combination of surface-exposed aromatic residues and acidic residues on SRSF1s RNA Recognition Motifs (RRMs) through electrostatic and cation-pi interactions. Analysis of RRM domains spanning the human proteome indicates that RRM domains involved in phase separation have more exposed aromatic residues and that in phase-separating proteins containing RS repeats, such residues are frequently surrounded by acidic residues. In addition to opening an avenue to previously unavailable proteins, our work provides insight into how SR proteins phase separate and participate in nuclear speckles.

biochemistry↗