Dynamic ruffling distortion of the heme substrate in non-canonical heme oxygenase enzymes.
Recent work by several groups has established that MhuD, IsdG, and IsdI are non-canonical heme oxygenases that induce significant out-of-plane ruffling distortions of their heme substrates enroute to mycobilin or staphylobilin formation. However, clear explanations for the observations of "nested" S = ½ VTVH MCD saturation magnetization curves at cryogenic temperatures, and exchange broadened (1)H NMR resonances at physiologically-relevant temperatures have remained elusive. Here, MCD and NMR data have been acquired for F23A and F23W MhuD-heme-CN, in addition to MCD data for IsdI-heme-CN, in order to complete assembly of a library of spectroscopic data for cyanide-inhibited ferric heme with a wide range of ruffling deformations. The spectroscopic data were used to evaluate a number of computational models for cyanide-inhibited ferric heme, which ultimately led to the development of an accurate NEVPT2/CASSCF model. The resulting model has a shallow, double-well potential along the porphyrin ruffling coordinate, which provides clear explanations for the unusual MCD and NMR data. The shallow, double-well potential also implies that MhuD-, IsdG-, and IsdI-bound heme is dynamic, and the functional implications of these dynamics are discussed.
Department of Chemistry, University of Vermont, Burlington, Vermont 05405, USA. matthew.liptak@uvm.edu.
Amanda B
AB
Graves
Department of Chemistry, University of Vermont, Burlington, Vermont 05405, USA. matthew.liptak@uvm.edu.
Erik H
EH
Horak
Department of Chemistry, University of Vermont, Burlington, Vermont 05405, USA. matthew.liptak@uvm.edu.
Matthew D
MD
Liptak
D001426:Bacterial Proteins / Q000737:chemistry*; D019295:Computational Biology; D018360:Crystallography, X-Ray; D003486:Cyanides / Q000737:chemistry*; D006418:Heme / Q000037:antagonists & inhibitors* / Q000737:chemistry*; D006419:Heme Oxygenase (Decyclizing) / Q000037:antagonists & inhibitors* / Q000737:chemistry*; D006899:Mixed Function Oxygenases / Q000737:chemistry*; D009169:Mycobacterium tuberculosis / Q000201:enzymology; D019906:Nuclear Magnetic Resonance, Biomolecular; D010105:Oxygenases / Q000737:chemistry*; D011487:Protein Conformation; D013696:Temperature
D001426:Bacterial Proteins; D003486:Cyanides; D006418:Heme; C497164:IsdI protein, Staphylococcus aureus; D006899:Mixed Function Oxygenases; D010105:Oxygenases; C482079:IsdG protein, Staphylococcus aureus; D006419:Heme Oxygenase (Decyclizing)