Binds to the host entry receptor YueB and triggers viral DNA ejection. Binding to Yueb. This interaction initiates a cascade of conformational changes at the gp21 C-terminus causing disassembly of the tail spike organization and opening of the cap region formed by the N-terminus of gp21. Interacts with host Yueb receptor; this interaction triggers viral DNA ejection. The N-terminus is part of the distal tail cap. The C-terminus is part of the spike structure and is probably involved in host receptor binding.