Retinoblastoma-associated protein, B-box (IPR002719)
Short name: RB_B
Overlapping homologous superfamilies
- Cyclin-like (IPR013763)
- Retinoblastoma-associated protein, B-box (IPR002719)
Retinoblastoma-like and retinoblastoma-associated proteins may have a function in cell cycle regulation. They form a complex with adenovirus E1A and SV40 large T antigen, and may bind and modulate the function of certain cellular proteins with which T and E1A compete for pocket binding. The proteins may act as tumor suppressors, and are potent inhibitors of E2F-mediated trans-activation. This domain has the cyclin fold [PMID: 8152925].
The crystal structure of the Rb pocket bound to a nine-residue E7 peptide containing the LxCxE motif, shared by other Rb-binding viral and cellular proteins, shows that the LxCxE peptide binds a highly conserved groove on the B-box portion of the pocket; the A-box portion (see IPR002720) appears to be required for the stable folding of the B box. Also highly conserved is the extensive A-B interface, suggesting that it may be an additional protein-binding site. The A and B boxes each contain the cyclin-fold structural motif, with the LxCxE-binding site on the B-box cyclin fold being similar to a Cdk2-binding site of cyclin A and to a TBP-binding site of TFIIB [PMID: 9495340].
The A and B boxes are found at the C-terminal end of the protein; the B-box is on C-terminal side of the A-box.
- PF01857 (RB_B)