Hmmmm. There are many association for this type of protein. Some say it's like a door. That kinda makes sense, in that both are a passage way that can opened and closed. Another association would be a short tunnel that allows the movement of stuff through a large solid body.
METAMIA is a free database of analogy and metaphor. Anyone can contribute or search. The subject matter can be anything. Science is popular, but poetry is encouraged. The goal is to integrate our fluid muses with the stark literalism of a relational database. Metamia is like a girdle for your muses, a cognitive girdle.