A 22-kDa protein (P22), a direct counterpart to mammalian ornithine decarboxylase antizyme (ODC-AZ), was found in Selenomonas ruminantium, a gram-negative and anaerobic bacterium from sheep rumen. P22 does not degrade lysine/ornithine decarboxylase (LDC/ODC) but does bind to the AZ-binding region of LDC/ODC and triggers ATP-dependent proteolysis. This proteolytic system is totally compatible with the factors implicated in the AZ-mediated regulatory systems of mammalian ODC, such as mouse AZ or 26S proteasomes. Surprisingly, P22 is an L10 protein, a component of the large subunit of the bacterial ribosome. Interestingly, our research on bacterial antizyme was originally initiated from the study on the peptidoglycan of S. ruminantium, which contained covalently linked cadaverine, representing quite unusual characteristic among bacterial cell wall. In this chapter, we describe the chemical structure and biological function of the cadaverine- containing peptidoglycan of S. ruminantium, and the cellular biosynthesis of cadaverine by LDC/ODC and its P22 (=L10)-mediated regulation. In addition, we briefly refer to the phylogenetic distribution of LDC/ODC and ribosomal L10 among bacteria.
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