Two birds with one stone: An antibiotic hit blocking Staphylococcus aureus heme uptake with serendipitous hemoglobin left-shifting activity

Infections caused by Staphylococcus aureus depend on its ability to access essential nutrients, including acquiring iron from human hemoglobin (Hb) through the iron-regulated surface determinant (Isd) system. The compound 4-[(2-{[5-(1H-indol-3-yl)-1,3,4-oxadiazol-2-yl]sulfanyl}acetyl)amino]benzoic acid (C35) was recently identified as a promising antimicrobial agent for its ability to bind Hb and hamper its interaction with the staphylococcal hemophore IsdB in vitro. Here, we show that C35 inhibits S. aureus growth by targeting the hemophore-driven iron-acquisition system, highlighting its potential as an inhibitor and validating hemophores as antibacterial targets. Furthermore, for drug design purposes, we solved the X-ray structure of Hb:C35 complex. In contrast to the predicted binding pose, C35 binds tetrameric Hb in a cleft between the α subunits, stabilizing a relaxed conformation (R2) and increasing Hb oxygen affinity. This serendipitous result hints to C35 as a promising scaffold for developing compounds with diverse, or even dual, therapeutic aims, with antimicrobial and Hb-modulating activity.