This is the N-terminal matrix-like domain (MA) of Activity-Regulated Cytoskeleton-Associated protein (Arc). This domain might be involved in stabilising the relative domain orientations of the capside-like domain (CA) upon capsid assembly. Arc is a regulator of synaptic scaling and dendrite remodelling [1].

1: The Capsid Domain of Arc Changes Its Oligomerization Propensity through Direct Interaction with the NMDA Receptor. Nielsen LD, Pedersen CP, Erlendsson S, Teilum K; Structure. 2019;27:1071-1081. PMID:31080121