Differential specificity for binding of retinoblastoma binding protein 2 to RB, p107, and TATA-binding protein

Area of Science:

• Molecular Biology
• Cell Biology
• Protein-protein Interactions

Background:

• The growth suppressor functions of retinoblastoma (RB) and p107 proteins are mediated by interactions with cellular proteins binding to their T/E1A pocket domain.
• Understanding these interactions is crucial for elucidating cellular growth regulation and transcription machinery.

Purpose of the Study:

• To investigate the binding properties of cellular retinoblastoma-binding protein 2 (RBP2) to RB, p107, and TATA-binding protein (TBP).
• To determine the functional role of specific domains within RBP2 in mediating these interactions.

Main Methods:

• Examination of RBP2 binding to RB, p107, and TBP using co-precipitation assays.
• Analysis of RBP2 mutants, including a mutation in the Leu-X-Cys-X-Glu motif.
• Identification of RBP2 binding sites through fragmentation and recombinant protein analysis.
• Assessment of RBP2's effect on RB-mediated suppression of E2F activity in vivo.

Main Results:

• RBP2 binds exclusively to the T/E1A pocket of p107.
• RBP2 interacts with RB via both T/E1A and non-T/E1A domains, and with TBP solely through a non-T/E1A domain.
• A mutation in RBP2's Leu-X-Cys-X-Glu motif abolished p107 binding but retained RB and TBP binding.
• A distinct 15-kDa fragment of RBP2 mediates RB and TBP binding but not p107 binding.
• Recombinant RBP2 preferentially precipitates active hypophosphorylated RB.
• RBP2 cotransfection reverses RB-mediated suppression of E2F activity in vivo.

Conclusions:

• RBP2 displays differential binding specificities towards RB, p107, and TBP.
• RBP2 possesses multifunctional domains enabling complex interactions with the cellular transcription machinery.
• These findings highlight the intricate regulation of cellular processes by protein-protein interactions involving RB family proteins.