The role of tricorn protease and its aminopeptidase-interacting factors in cellular protein degradation.

Tricorn protease was previously described as the core enzyme of a modular proteolytic system displaying multicatalytic activity. Here we elucidate the mode of cooperation between Tricorn and its interacting factors, and we identify two additional factors, F2 and F3, closely related aminopeptidases of 89 kDa. In conjunction with these three factors, Tricorn degrades oligopeptides in a sequential manner, yielding free amino acids. We have been able to reconstitute a proteolytic pathway comprising the proteasome, Tricorn, and its interacting factors, F1, F2, and F3, which converts proteins efficiently into amino acids. Therefore, it is quite likely that Tricorn also acts in vivo downstream of the proteasome and, in cooperation with its interacting factors, completes protein catabolic pathways.