Transthyretin-related proteins function to facilitate the hydrolysis of 5-hydroxyisourate, the end product of the uricase reaction.

Purine catabolic pathway in Bacillus subtilis is consisted of more than 14 genes. Among these genes, pucL and pucM are required for uricase activity. While PucL is known to encode the uricase itself, the function of PucM is still unclear although this protein is also indispensable for uric acid decomposition. Here, we provide evidence that PucM, a transthyretin-related protein, functions to facilitate the hydrolysis of 5-hydroxyisourate, the end product of the uricase reaction. Based on these results, we propose that transthyretin-related proteins present in diverse organisms are not functionally related to transthyretin but actually function as a hydroxyisourate hydrolase.