The Lyme disease pathogen Borrelia burgdorferi infects ∼500,000 people per year. The pathogen lacks primary metabolic pathways such as the TCA cycle and the fatty acid synthesis pathway. Because of this, many critical metabolites are sourced from the host. Despite being a metabolic minimalist, B. burgdorferi retains the mevalonate pathway, postulated to be necessary for the synthesis of the precursor for its peptidoglycan. While the mevalonate pathway and the enzyme that catalyzes its rate-limiting step (3-hydroxy-3-methyl glutaryl coenzyme A reductase, HMGR) are well studied in vertebrates due to their relevance in cholesterol biosynthesis, little is known about the importance of the pathway and its metabolite products in B. burgdorferi . Herein, we test the relevance of HMGR in B. burgdorferi . We employed CRISPR silencing to demonstrate that loss of HMGR results in a substantial reduction of cell proliferation and morphological defects that are ameliorated in the presence of exogenous mevalonate and IPP. We also report a comprehensive biochemical and structural characterization of the enzyme bound to substrate and products. Whereas statins are potent inhibitors of the human HMGR, their activities against bacterial HMGRs are muted. Given this difference in active sites, we explored the sequence conservation across all HMGR active sites and discovered a striking divergence outside of the catalytic residues. This difference can be leveraged for the design of species-specific active site inhibitors. Finally, bioinformatics revealed an evolutionary relationship between gram-stain, oligomerization and choice of cofactor in bacterial HMGRs, which led to the discovery of a subset of HMGRs that exhibit a level of cofactor plasticity highly unusual amongst oxidoreductases. Together, these findings elevate bacterial HMGRs as putative targets for narrow-spectrum antimicrobial development and reveal them as exemplary oxidoreductases to study the evolution of cofactor specificity.
Isaac Paddy (Sun,) studied this question.