1H and 119Sn magnetic resonance study of the SnIV protoporphyrin IX complex of equine myoglobin. Structure of the porphyrin-binding pocket.

The research investigates the structure of the SnPP complex with equine myoglobin using 1H and 119Sn nuclear magnetic resonance spectroscopy, revealing their interaction model that potentially contributes to treating hyperbilirubinemia.

Research Methodology and Findings

• The researchers used SnPP, a protoporphyrin complex associated in therapies for hyperbilirubinemia, combined with equine myoglobin (EqMb) to study their interaction. Hyperbilirubinemia is a condition characterized by an excess of bilirubin in the blood, and research indicates that SnPP could be effective in its treatment.
• The investigation was carried out using 1H and 119Sn nuclear magnetic resonance spectroscopy (NMR). NMR is a technique used to observe local magnetic fields around atomic nuclei, and it was applied here for determining the structure of the SnPP.EqMb complex.
• Through NMR, it was discovered that the SnPP.EqMb complex has almost the same porphyrin-binding pocket as EqMbCO, including the same porphyrin orientation in the major form of EqMbCO. A porphyrin is a group of organic compounds, one of which occurs in hemoglobin. A porphyrin-binding pocket refers to the site where a porphyrin molecule attaches itself within another compound.
• The use of 119Sn NMR spectroscopy also allows for the observation that the proximal His93F8-metal coordination is intact in SnPP.EqMb. This detail indicates that the His93F8 portion of the myoglobin maintains its correct spatial orientation relative to the metal atom in the SnPP.EqMb complex.
• Additionally, minor shifts in the side chain positions of certain residues were denoted, which might suggest the presence of water in the sixth coordination site, suggesting a slight adjustment in the structure due to the SnPP complex interaction.
• The stability of the SnPP.EqMb complex was confirmed as it remained unaltered at room temperature for weeks, further highlighting its potential for prolonged therapeutic use.
• Slow exchange rates for a large number of amide protons were also noted in the pH range of 7-9, suggesting possible resistances in proton exchange under these pH conditions, which could reflect on metabolic and cellular conditions.