B-267. Discovery of the Degradation Signal for Substrates of the Bacterial Proteasome from Mycobacterium tuberculosis

M. Pearce, J. Ferreyra, H. Darwin;
New York Univ. Med. Sch., New York, NY.

We have identified the first bacterial proteasome substrates in the human pathogen Mycobacterium tuberculosis: malonyl Co-A acyl carrier protein transacylase (FabD) and ketopantoate hydroxymethyltransferase (PanB). Maintenance of the physiological levels of these enzymes required proteasome protease activity in addition to the proteins Mpa (Mycobacterium proteasomal ATPase) and PafA (proteasome accessory factor A). A remaining question regarding bacterial proteasome physiology concerns how substrates are targeted for degradation. In the eukaryotic system, the small protein ubiquitin is covalently attached to proteasome substrates and acts as a targeting signal for delivery to the proteasome. Ubiquitin appears to be absent in prokaryotes, suggesting that there is a ubiquitin-independent mechanism for substrate targeting. To attempt to solve this mystery, we undertook comprehensive genetic and biochemical studies of our substrates to search for sequence elements that may play a role in substrate targeting. Through the use of two-hybrid analyses, truncation studies and chimera construction, we have uncovered an unexpected method of targeting substrates to the bacterial proteasome.