Kinetic Characterization of a Novel Fosfomycin Resistance Enzyme from Mycobacterium Bolletii

Abstract

Fosfomycin is a small antibiotic that is effective against both Gram-positive and Gram-negative bacteria via inhibition of cell wall formation. Fosfomycin resistance enzymes have been observed in both Gram-positive and Gram-negative bacteria: FosA, a M2+-dependent glutathione (GSH)-S-transferase found in Gram-negative species, FosB, a M2+- and K+-dependent bacillithiol (BSH)-S-transferase found in Gram-positive species, and the evolutionary precursor FosX, a M2+-dependent hydrolase also found in Gram-negative species. Each of these enzymes is activated by Mn2+ and inhibited by Zn2+. We have discovered, expressed, and purified a novel enzyme from Mycobacterium abscessus subspecies Bolletii that shares 55% sequence identity with FosX. Preliminary time trace kinetic data using 31P NMR suggest that this enzyme, which we call FosM, is also a M2+-dependent thiol transferase. Kinetic activity has been observed with both GSH and L-cysteine as thiol substrates. However, Mycobacteria do not produce GSH or BSH, and we believe FosM uses the natural thiol found in mycobacteria, mycothiol (MSH), as its substrate. Preliminary data also suggest that FosM is activated by Mn2+ and inhibited by Zn2+ similar to both FosA and FosB. Hydrolytic activity has also been observed, reinforcing that FosM may be an evolutionary descendant of FosX. We are currently trying to obtain MSH to demonstrate that FosM is a new class of fosfomycin resistance enzyme from Mycobacteria.