Structural studies of R2 and R2–like proteins with a heterodinuclear Mn/Fe cofactor and enzymes involved in Mycobacterium tuberculosis lipid metabolism

Abstract:

Tuberculosis is a notorious disease responsible for the deaths of 1.4 million people worldwide. A third of the world's population is infected with Mycobacterium tuberculosis, the bacterium causing the disease. The increase of multi drug-resistant strains worsens the situation, and the World Health Organization has declared tuberculosis to be a global emergency. The bacterium envelopes itself with a unique set of very long-chain lipids that play an important role in virulence and drug resistance. Therefore enzymes involved in lipid metabolism are putative drug targets. 

To allow entry into different metabolic pathways and transmembrane transport, fatty acids have to be activated. This is done primarily by fatty acyl-CoA synthetases (ACSs). We identified an ACS possibly involved in the bacterium’s virulence and solved its structure. Structural interpretation combined with previously reported data gives us insights into the details of its function. This enzyme is known to harbor lipid substrates longer than the enzyme itself, and we now propose how this peripheral membrane protein accommodates its substrates. 

Some of the most chemically challenging oxidations are performed by dinuclear metalloproteins belonging to the ferritin-like superfamily. We show that the ferritin-like protein, R2lox, from M. tuberculosis contains a new type of heterodinuclear Mn/Fe cofactor. This protein cofactor is capable of performing potent 2-electron oxidations as demonstrated by a novel tyrosine-valine crosslink observed in the protein. 

Recently a new subclass of ribonucleotide reductase (RNR) R2 proteins, was identified in the intracellular pathogen Chlamydia trachomatis containing the same type of Mn/Fe cofactor mentioned above. The RNR R2 proteins use their metal site to generate a stable radical, essential for the reduction of ribonucleotides to their deoxy forms, the building blocks of DNA. With this work, we were able to characterize the architecture of this metal cofactor.