Attaches the virion to the host receptor LamB, inducing viral DNA ejection. During tail assembly, initiates distal tail tip assembly by interacting with gpI, gpL and gpK. During virus entry to host cell, binds strongly to host LamB in an irreversible attachment. The binding induces structural changes in the tail leading to viral DNA injection through LamB trimeric pore. Interacts with host LamB.