title: NMR studies of the association of cytochrome b5 with cytochrome c.
abstract: In an effort to gain greater insight into the molecular mechanism of the electron-transfer reactions of cytochrome b(5), the bovine cytochrome b(5)-horse cytochrome c complex has been investigated by high-resolution multidimensional NMR spectroscopy using (13)C, (15)N-labeled cytochrome b(5) expressed from a synthetic gene. Chemical shifts of the backbone (15)N, (1)H, and (13)C resonances for 81 of the 82 residues of [U-90% (13)C,U-90% (15)N]-ferrous cytochrome b(5) in a 1:1 complex with ferrous cytochrome c were compared with those of ferrous cytochrome b(5) in the absence of cytochrome c. A total of 51% of these residues showed small, but significant, changes in chemical shifts (the largest shifts were 0.1 ppm for the amide (1)H, 1.15 for (13)C(alpha), 1.03 ppm for the amide (15)N, and 0.15 ppm for the (1)H(alpha) resonances). Some of the residues exhibiting chemical shift changes are located in a region that has been implicated as the binding surface to cyt c [Salemme, F. R. (1976) J. Mol. Biol. 10, 563-568]. Surprisingly, many of the residues with changes are not located on this surface. Instead, they are located within and around a cleft observed to form in a molecular dynamics study of cytochrome b(5) [Storch, E. M., and Daggett, V. (1995) Biochemistry 34, 9682-9693](.) The rim of this cleft can readily accommodate cytochrome c. Molecular dynamics simulations of the Salemme and cleft complexes were performed for 2 ns and both complexes were stable.
authors.affiliation: Department of Pharmaceutical Chemistry, University of California, San Francisco, California 94143, USA.
authors.forename: K
authors.initials: K
authors.lastname: Hom
authors.forename: Q F
authors.initials: QF
authors.lastname: Ma
authors.forename: G
authors.initials: G
authors.lastname: Wolfe
authors.forename: H
authors.initials: H
authors.lastname: Zhang
authors.forename: E M
authors.initials: EM
authors.lastname: Storch
authors.forename: V
authors.initials: V
authors.lastname: Daggett
authors.forename: V J
authors.initials: VJ
authors.lastname: Basus
authors.forename: L
authors.initials: L
authors.lastname: Waskell
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D001665:Binding Sites; D002247:Carbon Isotopes; D002417:Cattle; D003574:Cytochrome c Group / Q000737:chemistry*; D015786:Cytochromes b5 / Q000737:chemistry*; D005296:Ferrous Compounds / Q000737:chemistry; D006736:Horses; D008969:Molecular Sequence Data; D019906:Nuclear Magnetic Resonance, Biomolecular / Q000379:methods; D011487:Protein Conformation; D011522:Protons; D013816:Thermodynamics
chemical_list: D002247:Carbon Isotopes; D003574:Cytochrome c Group; D005296:Ferrous Compounds; D011522:Protons; D015786:Cytochromes b5