1H-NMR study of the mechanism of assembly and equilibrium heme orientation of sperm whale myoglobin reconstituted with protohemin type-isomers
| Autor: | Kevin M. Smith, Daniel W. Parish, Ravindra K. Pandey, Usha Pande, Jon B. Hauksson, Gerd N. La Mar, Jai P. Singh |
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| Rok vydání: | 1990 |
| Předmět: |
Hemeprotein
Magnetic Resonance Spectroscopy Stereochemistry Protein Conformation Protein reconstitution Biophysics Molecular Conformation Heme Biochemistry chemistry.chemical_compound Structure-Activity Relationship Structural Biology Animals Propionates Molecular Biology Pyrrole chemistry.chemical_classification Molecular Structure Chemistry Myoglobin Whales Propionate Hemin Hydrogen |
| Zdroj: | Biochimica et biophysica acta. 1041(2) |
| ISSN: | 0006-3002 |
| Popis: | The products of the incorporation of various protohemin type-isomers into the heme pocket of sperm whale myoglobin were investigated by 1 H-NMR in the met-cyano complexes, both immediately after reconstitution as well as at equilibrium. The type-isomers studied include those involving all possible interchanges of the two substituents on a given pyrrole. The protohemin-III and -XIII isomers, with true 2-fold symmetry, yielded only homogeneous products. Protohemins-XI, -XIV both exhibited two species after reconstitution, with one disappearing with time. Protohemin-I was the only asymmetric hemin that failed to exhibit two isomers initially. The orientation of the hemin within the pocket was established by nuclear Overhauser detected dipolar connectivities among heme substituents and between heme substituents and assigned heme pocket residues. At equilibrium, the heme orientations were dominated by the asymmetric propionate rather than vinyl dispositions on the hemin, with a clear preference for placing a propionate at the 8- vs. 5-methyl position of native myoglobin. For protohemin-XI, the propionates were found in the unexpected positions of the 7-propionate and 2-vinyl groups of native myoglobin, indicating that propionates can occupy positions well within the hydrophobic interior. The alternate heme orientation for the metastable intermediates detected for protohemin-XI and -XIV involved rotational isomerism about the α,γ- meso axes bisecting the vinyl positions, but these two axes are at right angles to each other in the protein matrix. The fact that protohemin-XIV, but not protohemin-I, exhibits a reversed orientation as a reconstitution intermediate provides direct evidence that vinyl contacts, as well as propionate links, modulate the relative stabilities of the initial encounter complexes between hemin and apomyoglobin. The heme cavity molecular/electronic structure was found largely unperturbed for the complexes of the various protohemin type-isomers. |
| Databáze: | OpenAIRE |
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