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 domain [1]. The B domain has a cyclin fold.

1: Structure of the retinoblastoma tumour-suppressor pocket domain bound to a peptide from HPV E7. Lee JO, Russo AA, Pavletich NP; Nature 1998;391:859-865. PMID:9495340