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FMRP is associated to the ribosomes via RNA
F Tamanini1, N Meijer, C Verheij
1MGC-Department of Clinical Genetics, Erasmus University, Rotterdam, The Netherlands.
Abstract:
The FMR1 transcript is alternatively spliced and generates different splice variants coding for FMR1 proteins (FMRP) with a predicted molecular mass of 70-80 kDa. FMRP is widely expressed and localized in the cytoplasm. To study a possible interaction with other cellular components, FMRP was isolated and characterized under non-denaturing conditions. Under physiological salt conditions FMRP appears to have a molecular mass of > 600 kDa, indicating a binding to other cellular components. This interaction is disrupted in the presence of high salt concentrations. The dissociation conditions to free FMRP from the complex are similar to the dissociation of FMRP from RNA as shown before. The binding of FMRP from the complex is also disrupted by RNAse treatment. That the association of FMRP to a high molecular weight complex possibly occurs via RNA, is further supported by the observation that the binding of FMRP, containing an lle304Asn substitution, to the high molecular weight complex is reduced. An equal reduced binding of mutated FMRP to RNA in vitro was observed before under the same conditions. The reduced binding of FMRP with the lle304Asn substitution further indicates that the interaction to the complex indeed occurs via FMRP and not via other RNA binding proteins. In a reconstitution experiment where the low molecular mass FMRP (70-80 kDa) is mixed with a reticulocyte lysate (enriched in ribosomes) it was shown that FMRP can associate to ribosomes and that this binding most likely occurs via RNA.
Insights
The Fragile X mental retardation protein (FMRP) binds to cellular components, likely via RNA, forming a large complex. This interaction is crucial for FMRP function and is disrupted by specific mutations.
Area of Science:
- Molecular Biology
- Cell Biology
- Genetics
Background:
- The FMR1 gene produces Fragile X mental retardation protein (FMRP), a 70-80 kDa protein found in the cytoplasm.
- FMRP's role in cellular processes is not fully understood, prompting investigation into its interactions.
Purpose of the Study:
- To investigate the molecular interactions and complex formation of FMRP under physiological conditions.
- To determine the role of RNA in FMRP complexation and its functional implications.
Main Methods:
- Non-denaturing isolation and characterization of FMRP.
- Salt concentration and RNAse treatments to disrupt FMRP complexes.
- In vitro binding assays with mutated FMRP and reconstitution experiments with reticulocyte lysate.
Main Results:
- FMRP exists as a high molecular weight complex (> 600 kDa) under physiological salt conditions, indicating association with other cellular components.
- Disruption of the complex occurs at high salt concentrations and upon RNAse treatment, suggesting RNA mediation.
- A specific FMRP mutation (Ile304Asn) reduced binding to the high molecular weight complex and to RNA in vitro.
- Reconstitution experiments showed FMRP associates with ribosomes, likely through RNA interactions.
Conclusions:
- FMRP forms large molecular complexes in the cytoplasm, predominantly through interactions with RNA.
- The Ile304Asn mutation impairs FMRP's ability to bind RNA and form these complexes.
- FMRP's association with ribosomes, likely via RNA, suggests a role in translational regulation.