Heme binding in the NEAT domains of IsdA and IsdC of Staphylococcus aureus

Absorption, magnetic circular dichroism (MCD), and electrospray mass spectral (ESI-MS) data are reported for the heme binding NEAr iron Transporter (NEAT) domains of IsdA and IsdC, two proteins involved in heme scavenging by Staphylococcus aureus. The mass spectrometry data show that the NEAT domains are globular in structure and efficiently bind a single heme molecule. In this work, the IsdA NEAT domain is referred to as NEAT-A, the IsdC NEAT domain is referred to as NEAT-C, heme-free NEAT-C is NEAT-A and NEAT-C are inaccessible to small anionic ligands. Reduction of the high-spin Fe(III) heme iron to 5-coordinate high-spin Fe(II) in NEAT-A results in coordination by histidine and opens access, allowing for CO axial ligation, yielding 6-coordinate low-spin Fe(II) heme. In contrast, reduction of the high-spin Fe(III) heme iron to 5-coordinate high-spin Fe(II) in NEAT-C results in loss of the heme from the binding site of the protein due to the absence of a proximal histidine. The absorption and MCD data for NEAT-A closely match those previously reported for the whole IsdA protein, providing evidence that heme binding is primarily a property of the NEAT domain.     

Investigations of differences in iron oxidation state inside single neurons from substantia nigra of Parkinson’s disease and control patients using the micro-XANES technique

X-ray absorption near edge structure spectroscopy was applied in order to investigate differences in iron chemical state between the nerve cells of substantia nigra (SN) representing Parkinson’s disease (PD) and those of control cases. Autopsy samples were cut using a cryotome, and were not fixed and not embedded in paraffin. The comparison of the absorption spectra near the iron K-edge measured in melanized neurons from SN of PD and control samples did not show significant differences in iron oxidation state. Measurements of inorganic reference materials containing iron in the second and third oxidation states indicate that most of the iron in all the nerve cell bodies examined was oxidized and occurred as trivalent ferric iron (Fe³⁺).