 This B subunit ring is also capable of binding to a receptor, usually a glycoprotein or a glycolipid, on the surface of the host cell.Without the B subunits, the A subunit has no way of attaching to or entering the cell, and thus no way to exert its toxic effect.Cholera toxin, shiga toxin, and SubAB toxin all have B subunits that are made up of five identical protein components, meaning that their B subunits are homopentamers.