New research sheds light on how RNA guanine content and G-quadruplex structures impact the phase behavior and material properties of biomolecular condensates, with implications for understanding cellular processes.
A study focusing on the Fragile X mental retardation protein (FMRP) reveals significant insights into how RNA sequences rich in guanine (G) impact the behavior of protein condensates. FMRP is known for its role in the development of Fragile X Syndrome, a neurodevelopmental disorder linked to intellectual disabilities and behavioral issues.
Researchers investigated four RNA sequences with varying guanine content and G-quadruplex (G4) propensity, observing that increasing G content triggers aggregation of poly-arginine while allowing all RNA sequences to support phase separation into liquid droplets with FMRP-LCR (low complexity region). These interactions are pivotal as they influence essential cellular processes, including mRNA trafficking and translational control.
In their methodology, the team employed various techniques, including microrheology and fluorescence recovery after photobleaching (FRAP), to quantify changes in viscosity and dynamics with increasing guanine content. Results indicated a moderate increase in viscosity and a decrease in dynamics correlating with higher G content, while the elasticity did not significantly differ with increasing G4 structure.
Remarkably, the methylation of FMRP reduced its binding affinity to RNA but did not significantly affect the properties of the condensates formed, suggesting that RNA sequence and structure are more critical than binding affinity in shaping condensate properties. This challenges existing assumptions about the direct influence of binding strength on condensate material characteristics.
The four RNA sequences analyzed included Sc1, a synthetic RNA aptamer that forms G4 structures; Sc1 mutant (Sc1-M), which disrupts G4 formation; Microtubule associated protein 1B (Map1B), a native binding partner of FMRP known for its higher guanine content; and Poly-Uridine 36 (pU36), used as a control.
Fluorescence intensity measurements showed that Sc1 and Map1B significantly outperformed the other RNA sequences in terms of G4-induced fluorescence, demonstrating the critical relationship between G4 formation and the material properties of the condensates.
The study highlights the importance of G-rich RNA structures in modulating the dynamics and stability of biomolecular condensates, which have implications beyond fragile X protein interactions, potentially affecting a broader range of cellular processes influenced by RNA binding proteins.
As FMRP condensates showed both dynamics and viscosity changes with different RNA structures, these findings prompt a reevaluation of how RNA contributes to the functionality and stability of protein condensates in neuron cells. Understanding these mechanisms could be key for developing therapeutic strategies for neurodevelopmental disorders like Fragile X Syndrome.
The research underscores the complex interplay between RNA sequences and protein interactions, paving the way for further studies exploring the biological significance of G-quadruplexes and their roles in health and disease.
