Polypyrimidine tract binding protein (PTB), an RNA binding protein containing four RNA recognition motifs (RRMs), is involved in both pre-mRNA splicing and translation initiation directed by picornaviral internal ribosome entry sites. Sequence comparisons previously indicated that PTB is a non-canonical RRM protein. The solution structure of a PTB fragment containing RRMs 3 and 4 shows that the protein consists of two domains connected by a long, flexible linker. The two domains tumble independently in solution, having no fixed relative orientation. In addition to the betaalphabetabetaalphabeta topology, which is characteristic of RRM domains, the C-terminal extension of PTB RRM-3 incorporates an unanticipated fifth beta-strand, which extends the RNA binding surface. The long, disordered polypeptide connecting beta4 and beta5 in RRM-3 is poised above the RNA binding surface and is likely to contribute to RNA recognition. Mutational analyses show that both RRM-3 and RRM-4 contribute to RNA binding specificity and that, despite its unusual sequence, PTB binds RNA in a manner akin to that of other RRM proteins.
PDB ID: 1QM9Download
MMDB ID: 13946
PDB Deposition Date: 1999/9/22
Updated in MMDB: 2007/10
Experimental Method:
solution nmr
Source Organism:
Similar Structures:
Biological Unit for 1QM9: monomeric; determined by author
Molecular Components in 1QM9
Label Count Molecule
Protein (1 molecule)
Polypyrimidine Tract-binding Protein(Gene symbol: PTBP1)
Molecule annotation
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Citing MMDB