Iron(III) located in the dinuclear metallo-β-lactamase IMP-1 by pseudocontact shifts

Heterodinuclear metalloenzymes are an important class of metalloproteins, but determining the location of the different metal ions can be difficult. Herein we present a new NMR spectroscopy method that uses pseudocontact shifts (PCS) to achieve this without assumptions about the coordinating ligands. The approach is illustrated with the dinuclear [FeZn] complex of IMP-1, which is a prototypical metallo-β-lactamase (MβL) that confers resistance to β-lactam antibiotics. Results from single-crystal X-ray diffraction were compromised by degradation during crystallization. With [GaZn]-IMP-1 as diamagnetic reference, the PCSs unambiguously identified the iron binding site in fresh samples of [FeZn]-IMP-1, even though the two metal centers are less than 3.8 Å apart and the iron is high-spin Fe³⁺, which produces only small PCSs. [FeZn]-MβLs may be important drug targets, as [FeZn]-IMP-1 is enzymatically active and readily produced in the presence of small amounts of Fe³⁺.