A protein is often not just amino acids, but also a bunch of so-called post-translational modifications(PTM). These could be carbohydrates that have distinct fu

A protein is often not just amino acids, but also a bunch of so-called post-translational modifications(PTM). These could be carbohydrates that have distinct functional roles, e.g. targeting. Members of different kingdoms have distinct PTMs which makes it difficult to just make a bacteria produce human protein. But bacteria you can modify genetically, human - not so much.