Acetylation at a lysine residue adjacent to the CtBP binding motif within adenovirus 12 E1A causes structural disruption and limited reduction of CtBP binding

Abstract

C-terminal binding protein (CtBP) has been shown to bind to a highly conserved five-amino-acid motif (PXDLS) located very close to the C-terminus of adenovirus early region 1A proteins. It has also been demonstrated that amino acids C-terminal and N-terminal to this original proposed binding site contribute to the interaction. However, conflicting evidence has been presented to show that acetylation of an adjacent lysine residue in Ad5E1A may or may not influence binding. It has now been demonstrated here that acetylation of a lysine, equivalent to position 261 in Ad12 E1A and position 285 in Ad5E1A, in a synthetic peptide disrupts the binding to CtBP1 and CtBP2 and alters the K i of the peptide, indicative of a reduction in the affinity of the peptide for CtBP1 and CtBP2, but only to a rather limited extent (less than 2-fold). The solution structures of synthetic peptides equivalent to wild-type and acetylated forms of the Ad12 E1A peptide have been determined by proton NMR spectroscopy. The wild-type form of the peptide adopts a series of β-turns over the region Val 254–Arg 262. Within the acetylated isoform, the β-turn conformation is less extensive, Val 260–Arg 262 adopting a random confirmation. We conclude that secondary structure (β-turns) and an appropriate series of amino acid side chains over an extended binding site (PXDLSXK) are necessary for recognition by CtBP, acetylation of lysine interfering with both of these features, but not to such an extent as to totally inhibit interaction. Moreover, it is possible that the β-turn conformation at the C-terminus of AdE1A contributes to binding to α importin and nuclear import. Acetylation of lysine 261 could disrupt interaction through structural destabilization as well as charge neutralization and subsequent nuclear localization.