Structure‐based drug design targeting the malty sweet Mycobacterium tuberculosis GlgE

Abstract

In 2016, 8.1 % of new cases (601,000 people) and 20 % of previously treated cases of Tuberculosis (TB) were diagnosed as Multiply Drug Resistant Tuberculosis (MDR‐TB) cases, amongst which 10 % are Totally Drug Resistant Tuberculosis (TDR‐TB) cases worldwide. In America, MDR‐TB new cases make 1.5 % of the cases among which none of the TDR‐TB cases were successfully treated in 2016. In addition to TB and HIV treatment being contraindicated, the rise of MDR‐TB and TDR‐TB emphasize the need for new drugs and drug targets. Identified in 2010, the maltosyltransferase GlgE is an interesting drug target in that it has no homologues in humans and its inhibition results in the death of the microorganism in 14 days. Based on the structure of GlgE's natural ligand, maltose‐1‐phosphate, and the known enzymatic mechanism, substrate and transition‐state analogs were designed as potential inhibitors of the enzyme and co‐crystallized with an MtbGlgE homolog. To improve the resolution of our X‐ray structures to more accurately analyze the interactions between the inhibitors and the residues in the active site, ScoGlgEI has been used as a surrogate. Sharing 53 % identity with MtbGlgE, we created a ScoGlgEI‐V279S variant as to obtain 100 % identity between the active sites of the two homologues. Based on the information obtained from X‐ray structures of ScoGlgEI‐V279S in complex with our initial inhibitor, 2,5‐dideoxy‐3‐O‐α‐D‐glucopyranosyl‐2,5‐imino‐D‐mannitol (DDGIM), a 2‐fold inhibition improvement has been made on our second‐generation inhibitors bringing the IC50 from 102 ± 8 μM to 45 ± 4 μM. Recently published, the crystal structures of ScoGlgEI‐V279S in complex with these early‐ and late‐dissociative transition‐state‐like inhibitors were solved at 2.5 Å and 3.2 Å showing that improvement was obtained through the addition of a phosphonate to our DDGIM inhibitor, resulting in an increased number of hydrogen bonded interactions between the enzyme and the inhibitors. To increase potency of our next generation inhibitor, additional interactions with the enzyme were sought outside the active site. The release of a structure of ScoGlgEI‐V279S in complex with its substrate brought more information to increase the number of interactions between ScoGlgEI‐V279S and the next generation of inhibitors. The details of the crystal structure of ScoGlgEI‐V279S in complex with our third‐generation inhibitor was obtained at 3.35 Å and the determined inhibitory activity will be discussed.Support or Funding InformationNIH grant AI105084This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.