Title
Dynamic Ruffling Distortion of the Heme Substrate in Non-Canonical Heme Oxygenase Enzymes
Author
Amanda B. Graves, Erik H. Horak, Matthew D. Liptak
Year
2016
Journal
Dalton Transactions
Abstract
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 1H 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 implicatons of these dynamics are discussed.
Instrument
J-815
Keywords
Circular dichroism, Magnetic circular dichroism, Protein folding, Coordination chemistry, Biochemistry