Structural basis for the recognition of the E2F transactivation domain by the retinoblastoma tumor suppressor

Abstract

Repression of E2F transcription activity by the retinoblastoma (Rb) tumor suppressor through its interaction with the transactivation domain of the E2F transcription factor is one of the central features of G1/S arrest in the mammalian cell cycle. Deregulation of the Rb-E2F interaction results in hyperproliferation, lack of differentiation, and apoptosis, and can lead to cancer. The 2.2-Å crystal structure of the Rb pocket complexed with an 18-residue transactivation-domain peptide of E2F-2 reveals that the boomerang-shaped peptide binds to the highly conserved interface between the A-box and the B-box of the Rb pocket in a bipartite manner. The N-terminal segment of the E2F-2 peptide in an extended ␤-strand-like structure interacts with helices from the conserved groove at the A-B interface, whereas the C-terminal segment, which contains one 3 10 helix, binds to a groove mainly formed by A-box helices. The flexibility in the middle of the E2F-2 peptide is essential for the tight association of E2F to the Rb pocket. The binding of Rb to the E2F-2 peptide conceals several conserved residues that are crucial for transcription activation of E2F. We provide the structural basis for the Rb-mediated repression of E2F transcription activity without the requirement of histone-modifying enzymes.

Structural mechanisms of DREAM complex assembly and regulation

“…Each subdomain contains a fivehelix cyclin fold flanked by additional helices that form the A-B interface or the LxCxE interface or cover hydrophobic surfaces. As with previous Rb pocket domain structures (Lee et al 1998(Lee et al , 2002Xiao et al 2003;Balog et al 2011), most residues in the central loop between the two subdomains were left out of the crystallized construct, and the residues that remain are not visible in the electron density.…”

“…The pocket domain contains two protein interaction interfaces: the LxCxE cleft and the E2F transactivation domain (E2F TD )-binding site (Lee et al 1998(Lee et al , 2002Xiao et al 2003;Dick and Rubin 2013). The LxCxE cleft binds viral and endogenous proteins containing an LxCxExφ sequence motif (x is any amino acid, and φ is a hydrophobic amino acid) (Jones et al 1990;Lee et al 1998;Singh et al 2005).…”

Retinoblastoma family proteins as key targets of the small DNA virus oncoproteins

“…The binding site for this motif is contained within the pRb pocket, but is distinct from the LxCxE binding groove (Lee et al, 1998;Kim et al, 2001). Recent studies have determined the crystal structure of pRb A-B pocket bound to either the E2F (409-426) or the E2F-2 (410-427) peptide (Lee et al, 2002;Xiao et al, 2003). As anticipated by genetic and structural considerations (Lee et al, 1998), the boomerang-shaped E2F (409-426) peptide binds to a highly conserved groove on the surface of the central interface connecting the A and B boxes.…”

“…As a consequence of the high conservation, between different species and among pocket protein members, shown by the structural features of pRb that interact with E1A CR1 and CR2, the other members of the pocket protein family p107 and pRb2/p130 interact in a similar way with E1A conserved regions (Lee et al, 1998;Lee et al, 2002;Xiao et al, 2003).…”

Reduction of apoptosis in Rb-deficient embryos via Abl knockout

“…The interaction between RB and the C-terminal peptide of E2F-1, E2F-2 and E2F-3 has been elucidated by X-ray crystallography to involve the RB A/B domain (Lee et al, 2002;Xiao et al, 2003). The crystal structure of a shallow groove in the RB B-domain binding to the LxCxE-peptide found in viral oncoproteins such as E7 has also been solved (Lee et al, 1998;Liu et al, 2006).…”