Part of the ecpRABCDE operon, which encodes the E.coli common pilus (ECP). ECP plays a dual role in early-stage biofilm development and host cell recognition. Major subunit of the fimbria (By similarity). Self-associates. Forms filaments. Interacts with EcpD (By similarity). Positively regulated by EcpR. Belongs to the EcpA/MatB fimbrillin family.