This is the C-terminal domain of Arc protein present in found in Rattus norvegicus. The Arc protein modulates the trafficking of AMPA-type glutamate receptors. This domains tertiary structure is similar to the capsid domain of HIV gag protein. The domain is thought to have evolved from the capsid domain of Ty3/Gypsy retrotransposon [1].

1: Structural basis of arc binding to synaptic proteins: implications for cognitive disease. Zhang W, Wu J, Ward MD, Yang S, Chuang YA, Xiao M, Li R, Leahy DJ, Worley PF; Neuron. 2015;86:490-500. PMID:25864631