To learn more and confirm the inhibitory mechanism and the basis for its species selectivity, Dr. Huilin Li, co-author and biophysicist from Broohaven National Laboratory in Upton, New York, and his group determined the atomic-level crystal structures of TB proteasomes following exposure to the inhibitors. These studies were performed at the National Synchrotron Light Source (NSLS) -- a source of intense x-ray, ultraviolet, and infrared light beams at Brookhaven Lab.
The structural studies revealed that the inhibitor molecules block the proteasome's ability to degrade proteins in more than one way: by producing a direct chemical change to the proteasome active site, and by altering the conformation of the "pocket" into which protein fragments bind before being degraded.
"This conformational change constricts the pocket to the point that it cannot accommodate a protein substrate," said Li. "The many amino acid residues of the TB proteasome involved in this conformational change, some far away from the active site, are different from those in human proteasomes. This might explain why such dramatic inhibition is not observed in the human proteasome, as the human enzyme may not be able to undergo the same structural change."
A detailed understanding of the steps by which these inhibitors cause the conformational changes could therefore guide the design of the next generation of anti-TB drugs.
This research was funded by grants from the National Institutes of Health (NIH) and the Milstein Program in Chemical Biology of Infectious Diseases at Weill Cornell Medical College. The NSLS at Brookhaven Lab is supported by the Office of Basic Energy Sciences within the DOE Office of Science.
Additional co-authors include Luiz Pedro Sorio de Carvalho, Hui Tao, Guillaume Vogt, Kangyun Wu, Jean Schneider, Tamutenda Chidawanyika, J. David Warren, all from Weill Cornell; Dongyang Li from the Brookhaven National Laboratory, Upton, NY.
Source: New York- Presbyterian Hospital/Weill Cornell Medical Center/Weill Cornell Medical College