An example of this class of protein is PRB4 (IB5), a human parotid salivary protein known to bind with polyphenols (binding responsible for the astringency mouth feel).
Tannin binding
Many tannin-consuming animals secrete a tannin-binding protein (mucin) in their saliva. Tannin-binding capacity of salivary mucin is directly related to its proline content. Advantages in using salivary proline-rich proteins (PRPs) 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.