The two PAN ATPases from Halobacterium display N-terminal heterogeneity and form labile complexes with the 20S proteasome

摘要

pThe PAN (proteasome-activating nucleotidase) proteins from archaea represent homologues of the eukaryotic 26S proteasome regulatory ATPases. iIn vitro/i the PAN complex has been previously shown to have a stimulatory effect on the peptidase activities of the 20S core. By using gradient ultracentrifugation we found that, in cellular extracts, the two PAN proteins from iHalobacterium/i do not form stable high-molecular-mass complexes. Only PAN B was found to associate transiently with the 20S proteasome, thus suggesting that the two PAN proteins are not functionally redundant. The PAN B–20S proteasome complexes associate in an ATP-dependent manner and are stabilized upon nucleotide binding. The two PAN proteins were immunodetected in cellular extracts as N-terminal-truncated polypeptides. RNA-mapping experiments and sequence analysis indicated that this process involved transcript heterogeneities and dual translational initiation mechanisms. Taken together, our results suggest that PAN N-terminal modifications and their intracellular dynamics of assembly/association may constitute important determinants of proteolysis regulation./p