Proline rich protein

Proline-rich proteins are a class of intrinsically disordered proteins containing several repeats of a short proline-rich sequence.
Many tannin-consuming animals secrete a tannin-binding protein in their saliva. Tannin-binding capacity of salivary mucin is directly related to its proline content. Advantages in using salivary proline-rich proteins to inactivate tannins are:

PRPs inactivate tannins to a greater extent than do dietary proteins; this results in reduced fecal nitrogen losses,
PRPs contain non specific nitrogen and nonessential amino acids; this makes them more convenient for an animal to exploit rather than using up valuable dietary protein.

Example of this class of protein is IB5, a human parotid salivary protein known to bind with polyphenols. Other examples include Proline-Rich 12, Proline-Rich Protein 30, and Proline-Rich Protein 21.