Tetratricopeptide repeats in the anaphase‐promoting complex provide multiple activator binding sites

Abstract

The anaphase‐promoting complex (APC) is a 13‐subunit ubiquitin ligase that initiates the final events of mitosis. Substrates are recruited to the APC by an activator protein (Cdc20 or Cdh1). We tested the possibility that activator binding to the APC depends on three related APC subunits (Cdc27, Cdc16, and Cdc23) that contain multiple tetratricopeptide repeats (TPRs): repeated 34 amino acid sequences that often fold into hydrophobic grooves used for protein‐protein interactions. Each subunit contains 9–10 TPRs, which together may form a large array of TPRs on the APC surface. To assess the function of this array, we mutated residues predicted to lie in the TPR grooves of Cdc27, Cdc16, and Cdc23. Mutation of single residues in the grooves of Cdc27 or Cdc23 reduced the ability of the activators Cdh1 and Cdc20 to bind and activate purified APC. Subunit binding and APC integrity were unaffected. The mutations suppressed the lethality of activator overexpression in yeast. We propose that the presence of multiple activator binding sites may explain how the APC can make specific yet flexible interactions with a wide variety of substrates. Supported by NIH GM53270 and an NSF fellowship.