Structural basis for the development of potential inhibitors targeting FadD23 from <i>Mycobacterium tuberculosis</i>

Sulfolipid-1 (SL-1) is a lipid that is abundantly found in the cell wall of Mycobacterium tuberculosis ( Mtb ). Mtb FadD23 is crucial in the SL-1 synthesis pathway. Previously, 5′- O -[ N -(11-phenoxyundecanoyl)sulfamoyl]adenosine (PhU-AMS) has been shown to be a general inhibitor of fatty-acid-adenylating enzymes (FadDs) in Mtb . However, the fatty acyl-AMP ligase (FAAL) class of FadDs, which includes Mtb FadD23, appears to be functionally nonredundant in the production of multiple fatty acids. In this study, the ability of PhU-AMS to bind to Mtb FadD23 was examined under in vitro conditions. The crystal structure of the Mtb FadD23–PhU-AMS complex was determined at a resolution of 2.64 Å. Novel features were identified by structural analysis and comparison. Although PhU-AMS could bind to Mtb FadD23, it did not inhibit the FAAL adenylation activity of Mtb FadD23. However, PhU-AMS improved the main T m value in a differential scanning fluorimetry assay, and a structural comparison of Mtb FadD23–PhU-AMS with FadD32 and PA1221 suggested that PhU-AMS blocks the loading of the acyl chain onto Pks2. This study sheds light on the structure-based design of specific inhibitors of Mtb FadD23 and general inhibitors of FAALs.