Derivation of the Ancestral Proteins of the NMD A receptor complex: an insight on the origin of human intelligence using Bayesian tools

Abstract

Little is known about the exact origin of intelligence in more evolved organisms, especially the higher vertebrates. On the contrary, the post-synaptic density and its components are widely studied because of their importance to neural communication. Members of the NMDA-receptor complex and MAGUK proteins largely involved in mammalian synaptic plasticity and transmission are being characterized based on structure and function. While some proteins of the PSD are found to exist in lower organisms such as Monosiga brevicolis, Saccharomyces cerevisiae, Nematostella vectensis and Amphimedon queenslanidca, the functions of the proteins in these organisms are either different or not well-understood. For this study, seven sets of protein sequences for six representative organism groups were retrieved and analyzed to determine a theoretical ancestral sequence. Homology search was also performed to determine which proteins were most similar to the ancestral sequence; furthermore, a 3-D structure prediction was done in order to assist in the explanation of the protein’s functions. Results showed the proteins to be homologous to sequences existing in unicellular organisms such as bacteria, archaea, apicomplexans, and yeast, with several sequences being almost fully conserved. However, research indicated that functions of some proteins were different in the unicellular context. This supported the claim that while intelligence itself may not have originated from unicellular organisms, structurally similar proteins that have since evolved to become functional in mammalian synaptic plasticity and transmission trace back its ancestry to simpler organisms that appeared on the early Earth.