Poster abstracts

Poster number 37 submitted by MaKenzie Scarpitti

Translational control by the fragile X mental retardation protein, FMRP

MaKenzie R. Scarpitti 1,2 (1Department of Biological Chemistry and Pharmacology, 2Center for RNA Biology, The Ohio State University, Columbus, OH 43210), Michael Kearse 1,2 (1Department of Biological Chemistry and Pharmacology, 2Center for RNA Biology, The Ohio State University, Columbus, OH 43210)

Abstract:
Fragile X syndrome is caused by the loss of expression of the fragile X mental retardation protein (FMRP). Loss of functional FMRP is the leading monogenic cause of autism spectrum disorders and intellectual disability. FMRP is an RNA-binding protein that is thought to inhibit translation elongation of its target transcripts, supporting the hypothesis that FXS is caused by an imbalance in protein synthesis at neuronal synapses. In neurons, FMRP must achieve a certain degree of specificity to facilitate healthy neuronal development and maintenance. Biochemical binding assays indicate that specific RNA-binding domains of FMRP have high affinity to structured RNAs, such as pseudoknots and G-quadruplexes. Global analysis of FMRP mRNA binding shows an extreme preference to the coding sequence. These data support the leading model in the field—FMRP is targeted to mRNAs by affinity to structures within mRNA coding regions and stalls elongating ribosomes to inhibit translation elongation. However, work over the years from multiple groups shows that FMRP inhibits in vitro translation of every mRNA tested. Here, we directly test if FMRP uses RNA secondary and tertiary structure to target specific transcripts for translation elongation inhibition. Our preliminary data indicate that FMRP in fact does not require pseudoknots nor G-quadruplexes in coding regions to inhibit translation. Biochemical dissection of FMRP suggests that the last two domains, which are an annotated RGG box and an unstructured and positively charged C-terminal domain, contain the translational inhibition activity. However, each domain alone cannot inhibit translation in vitro. These data point toward a mechanism where the RGG box and C-terminal domains work synergistically to inhibit translation, directly challenging the leading model of FMRP-mediated translation inhibition.

Keywords: RNA binding protein, Fragile X mental retardation protein, Translation elongation