title: NMR study of the active site of shark met-cyano myoglobins.
abstract: The myoglobins from the sharks Galeorhinus japonicus and Musterus japonicus possess a distal Gln-E7 instead of the usually found His-E7. The met-cyano form of these shark myoglobins has been studied by 1H- and 15N-NMR in order to gain insight into the functional properties of the Gln-E7. The analysis of paramagnetic relaxation has provided the assignment of the resonance arising from one of the Gln-E7 N epsilon H labile protons, whilst the rate of its chemical exchange has been analyzed in detail by using a saturation transfer method. The hydrogen-bonding interaction between this proton and Fe-bound-CN(-) has been clearly manifested in the hyperfine shift of the Gln-E7 N epsilon H proton resonance as well as its chemical exchange behavior. The resonances of the Gln-E7 side-chain non-labile protons have been partly assigned on a basis of both scalar and dipolar connectivities. The analysis of the dipolar connectivities among the side-chain protons and the iron-proton distances determined from their paramagnetic relaxation rate has revealed that the side chain adopts a conformation with its carbonyl oxygen oriented away from the heme. Although (1)H-NMR spectra of these two myoglobins are essentially similar, a relatively large difference in the shift of Gln-E7 N(epsilon)H proton and Fe-bound C15 N- resonances between the two has been observed which is attributed to a differential hydrogen-bonding interaction between these proteins. The present study demonstrates the sensitivity of NMR parameters to the hydrogen-bonding interaction between coordinated ligand and a distal amino-acid side chain in paramagnetic hemoproteins.
authors.affiliation: Department of Chemistry, University of Tsukuba, Japan.
authors.forename: Y
authors.initials: Y
authors.lastname: Yamamoto
authors.forename: T
authors.initials: T
authors.lastname: Suzuki
mesh_terms: D000818:Animals; D001665:Binding Sites; D005973:Glutamine / Q000737:chemistry; D006860:Hydrogen Bonding; D006863:Hydrogen-Ion Concentration; D007501:Iron / Q000737:chemistry; D009682:Magnetic Resonance Spectroscopy; D008786:Metmyoglobin / Q000737:chemistry*; D015394:Molecular Structure; D009211:Myoglobin / Q000031:analogs & derivatives* / Q000737:chemistry; D011522:Protons; D012754:Sharks / Q000378:metabolism*
chemical_list: D009211:Myoglobin; D011522:Protons; C086756:myoglobin cyanide; D005973:Glutamine; D008786:Metmyoglobin; D007501:Iron