Yet, the TonB box is in an extended conformation and, curiously, makes few contacts with the rest of the protein — it protrudes down into the periplasmic space, just inside the wall of the barrel.

The algae produces the hormone in its periplasmic space, a kind of permeable membrane where the enzyme is located. "This is interesting because, from there, it can release the hormone outside to ...

multilayered film comparable to the typical cell envelope of Gram-negative bacteria, which comprises a cytoplasmic membrane (CM), a periplasmic space (PS) and an outer membrane (OM).