Does the Asiatic black bear (Ursus thibetanus) have the ability to secrete tannin-binding salivary proteins?

Abstract

Asiatic black bears (Ursus thibetanus) feed on acorns, such as Quercus crispula and Q. serrata, to store fat during autumn. However, tannins, astringent polyphenols, contained in the acorns are known to have negative effects, such as reduction in protein digestibility and gastrointestinal tract failure, on acorn consumers and it is unknown how the bears respond to tannins.

We analyzed the parotid gland of black bears and found that they were capable of secreting proline-rich proteins (PRPs), which belong to a group of tannin-binding salivary proteins. Black bear PRPs contained 25% proline and their relative affinity to tannins extracted from Q. serrata was thirteen times higher than that of bovine serum albumin. The parotid glands of black bear were hypertrophied in autumn, and the PRPs concentration in the parotid glands increased at the same time.