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1H NMR Study of the Influence of Hemin Vinyl→Methyl Substitution on the Interaction between the C-Terminus and Substrate and the “Aging” of the Heme Oxygenase from Neisseria meningitidis: Induction of Active Site Structural Heterogeneity by a Two-Fold Symmetric Hemin†
journal contribution
posted on 2006-11-21, 00:00 authored by Yangzhong Liu, Li-Hua Ma, Xuhong Zhang, Tadashi Yoshida, James D. Satterlee, Gerd N. La MarSolution 1H NMR has been used to characterize the active site molecular and electronic structure
of the cyanide-inhibited 2,4-dimethyldeuterohemin complex of the heme oxygenase from Neisseria
meningitidis (NmHO) with respect to the mode of interaction of the C-terminus with the substrate and the
spontaneous “aging” of NmHO that results in the cleavage of the C-terminal Arg208-His209 dipeptide.
The structure of the portion involving residues Ala12-Phe192 is found to be essentially identical to that
of the protohemin complex in either solution or crystal. However, His207 from the C-terminus is found
to interact strongly with the substrate 1CH3, as opposed to the 8CH3 in the protohemin complex. The
different mode of interaction of His207 with the alternate substrates is attributed to the 2-vinyl group of
protohemin sterically interfering with the optimal orientation of the proximal helix Asp27 carboxylate
that serves as acceptor to the strong H-bond by the peptide of His207. The 2,4-dimethyldeuterohemin HO
complex “ages” in manner similary to that of protohemin, (Liu, Y., Ma, L.-H., Satterlee, J.D., Zhang, X.,
Yoshida, T., and La Mar, G. N., (2006) Biochemistry 45, 3875−3886) with mass spectrometry and
N-terminal sequencing indicating that the Arg208-His209 dipeptide is cleaved. The 2,4-dimethyldeuterohemin complex of WT HO populates an equilibrium isomer stabilized in low phosphate concentration for
which the axial His imidazole ring is rotated by ∼20° from that in the WT. The His ring reorientation is
attributed to Asp24 serving as the H-bond acceptor to the His207 peptide NH, rather than to the His23
ring NδH as in the crystals. The functional implications of the altered C-terminal interaction with substrate
modification are discussed.
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Keywords
Neisseria meningitidisimidazole ringhelix Asp 27 carboxylatephosphate concentrationmodeArgWT HO populatesheme oxygenasemass spectrometryequilibrium isomerdimethyldeuterohemin1 H NMR StudyHeminacceptorinteractionprotohemin sterically8 CH 3dipeptideJ.D207 peptide NHNmHOmanner similarysubstrate modificationcrystalActive Site Structural Heterogeneityring reorientationHeme Oxygenase23 ring N δHLa MarAsp 24
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