Identification of a 22-kDa protein required for the degradation of Selenomonas ruminantium lysine decarboxylase by ATP-dependent protease

In Selenomonas ruminantium, a strictly anaerobic, Gram-negative bacterium isolated from sheep rumen, a rapid degradation of lysine decarboxylase (LDC) occurred on entry into the stationary phase of cell growth. Here, we identified a 22-kDa protein as a stimulating factor for the degradation of LDC, which was catalyzed by ATP-dependent protease(s) in S. ruminantium. The purified 22-kDa protein preparation itself had no degradation activity towards LDC but it was required for the degradation of LDC by ATP-dependent proteases in a cell-free system. The 22-kDa protein had similar biochemical and biophysical characteristics to those of antizyme, the regulator for the degradation of mammalian ODC, which had been reported only in mammalian cells. From the sequencing data of the N-terminal 30 amino acid residues of the 22-kDa protein preparation, 22-kDa protein was found to be a new protein which was distinguished from antizyme. This is the first report of the presence of an antizyme-like regulator protein in a prokaryote.