High affinity between CREBBP/p300 and NCOA evolved in vertebrates

The interaction between the transcriptional coactivators CREBBP/p300 and NCOA is governed by two intrinsically disordered domains called NCBD and CID, respectively. The CID domain emerged within the NCOA protein in deuterostome animals (including vertebrates) after their split from the protostomes (molluscs, worms, and arthropods). However, it has not been clear at which point a high affinity interaction evolved within the deuterostome clade and whether all present-day deuterostome animals have a high affinity NCBD:CID interaction. We have here expressed and measured affinity for NCBD and CID domains from animal species representing different evolutionary branches of the deuterostome tree. While all vertebrate species have high-affinity NCBD:CID interactions we found that the interaction in the echinoderm purple sea urchin is of similar affinity as that of the proposed ancestral domains. Our findings demonstrate that the high-affinity NCBD:CID interaction likely evolved in the vertebrate branch and question whether the interaction between CREBBP/p300 and NCOA is essential in nonvertebrate deuterostomes. The data provide an example of evolution of transcriptional regulation through protein-domain based inventions.