The N-terminus of the fragile X mental retardation protein contains a novel domain involved in dimerization and RNA binding.
Fragile X syndrome, the most common cause of inherited mental retardation, is caused by the absence of the fragile X mental retardation protein (FMRP). The emerging picture is that FMRP is involved in repression of translation through a complex network of protein-protein and protein-RNA interactions. Very little structural information is, however, available for FMRP that could help to understand its function. In particular, no structural studies are available about the N-terminus of the protein, a highly conserved region which is involved in several molecular interactions. Here, we explore systematically the ability of the FMRP N-terminus to form independently folded units (domains). We produced deletion mutants and tested their fold and functional properties by mutually complementary biophysical and biochemical techniques. On the basis of our data, we conclude that the N-terminus contains a domain, that we named NDF, comprising the first 134 amino acids. Most interestingly, NDF comprises two copies of a newly identified Agenet motif. NDF is thermally stable and has a high content of beta structure. In addition to being able to bind to RNA and to recognize some of the FMRP interacting proteins, NDF forms stable dimers and is able to interact, although weakly, with the full-length protein. Our data provide conclusive evidence that NDF is a novel motif for protein-protein and protein-RNA interactions and contains a previously unidentified dimerization site.
Adinolfi
S
S
National Institute for Medical Research, The Ridgeway, NW7 1AA London, UK.
Ramos
A
A
Martin
S R
SR
Dal Piaz
F
F
Pucci
P
P
Bardoni
B
B
Mandel
J L
JL
Pastore
A
A
D000595:Amino Acid Sequence; D019281:Dimerization; D051860:Fragile X Messenger Ribonucleoprotein 1; D005600:Fragile X Syndrome / Q000235:genetics / Q000378:metabolism; D006801:Humans; D008969:Molecular Sequence Data; D009154:Mutation; D009419:Nerve Tissue Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D017510:Protein Folding; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D012313:RNA / Q000378:metabolism*; D016601:RNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D016415:Sequence Alignment
D051860:Fragile X Messenger Ribonucleoprotein 1; D009419:Nerve Tissue Proteins; D012313:RNA; D016601:RNA-Binding Proteins; C497683:FMR1 protein, human