Like Looking in a Mirror -- Duke News Article
Author Summary. Antimicrobial resistance is a major healthcare crisis. While we were developing novel enzyme inhibitors to combat methicillin-resistant Staphylococcus aureus (MRSA), we found that the chirality of both inhibitor and cofactor can have a large influence on inhibitor potency. Our detailed study of enantiomeric propargyl-linked antifolates (PLAs) shows that the chiral state of inhibitors can affect the chiral state of the cofactor. Moreover, the bacterial enzyme target can exploit cooperative chirality to evade inhibitor binding. We call this phenomenon chiral evasion. Using crystal structures, biochemical assays, computational protein design algorithms, and statistical mechanics, a detailed mechanism for chiral evasion is proposed. While the concept that different enantiomers have different biology is well known, MRSA is unique: we do not know of any other cases where a single mutation (F98Y) flips the chirality preference for cofactor binding and induces stereospecificity for drug binding. Thus, we illuminate the effect of this clinically relevant resistance mutation on the obligate cofactor binding site. These new insights will be useful to develop more durable antibiotics that are resilient to resistance.
Abstract.
Antimicrobial resistance presents a significant health care crisis. The mutation F98Y in
Staph. aureus dihydrofolate reductase (SaDHFR) confers resistance to the
clinically important antifolate trimethoprim (TMP). Propargyl-linked antifolates
(PLAs), next generation DHFR inhibitors, are much more resilient than TMP against
this F98Y variant, yet this F98Y substitution still reduces efficacy of these agents.
Surprisingly, differences in the enantiomeric configuration at the stereogenic center of
PLAs influence the isomeric state of the NADPH cofactor. To understand the molecular
basis of F98Y-mediated resistance and how PLAs' inhibition drives NADPH isomeric
states, we used protein design algorithms in
the
Image above: Left: 1H-1H COSY NMR spectrum of tricyclic NADPH (t-NADPH). Right: Structure of S. aureus dihydrofolate reductase (DHFR) with inhibitor R-27 (top, white) and t-NADPH (bottom, black). DHFR exploits this alternate anomeric configuration of NADPH to evade inhibition by certain inhibitors. Image created by Graham, Santosh, and Bruce.
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