A fragment profiling approach to inhibitors of the orphan $\textit{M. tuberculosis}$ P450 CYP144A1

Similarity in the ligand binding profile of two enzymes may provide insight for functional characterization and be of greater relevance to inhibitor development than sequence similarity or structural homology. Fragment screening is an efficient approach to characterizing the ligand profile of an enzyme and has been applied here to study the family of cytochrome P450 enzymes (P450s) expressed by Mycobacterium tuberculosis (Mtb). The Mtb P450s have important roles in bacterial virulence, survival and pathogenicity. Comparing the fragment profiles of seven of these enzymes revealed that P450s which share a similar biological function have significantly similar fragment profiles, while functionally unrelated or orphan P450s exhibit distinct ligand binding properties, despite overall high structural homology. Chemical structures that exhibit promiscuous binding between enzymes have been identified, as have selective fragments that could provide leads for inhibitor development. The similarity in the fragment binding profile of the orphan enzyme CYP144A1 to CYP121A1, an enzyme important for Mtb viability, provides a case study illustrating the subsequent identification of novel CYP144A1 ligands. The different binding modes of these compounds to CYP144A1 provide insight into structural and dynamic aspects of the enzyme, suggest a hypothesis into biological function and provide opportunity for inhibitor development. Expanding this fragment profiling approach to include a greater number of functionally characterized and orphan proteins may provide a valuable resource for understanding enzyme-ligand interactions.M.E.K. was supported by a Commonwealth (University of Cambridge) Scholarship awarded in conjunction with the Cambridge Commonwealth Trust and Cambridge Overseas Trust. J.C. was supported by funding from the William D Ford program from the US Department of Education. K.J.M. and A.G.C. was supported by grants from the BBSRC (Grant No: BB/K001884/1 and BB/I019227/1). A.Z. was funded by the European Research Commission (ERC Starting Grant 2012 MIXTURE)