title: Backbone dynamics of azurin in solution: slow conformational change associated with deprotonation of histidine 35.
abstract: 15N relaxation measurements have been performed on the type Iota blue copper protein azurin from Pseudomonas aeruginosa. The relaxation times show that one loop (residues 103-108) and one turn (residues 74-77) display fast internal motions. The rest of the protein is rigid with an average order parameter S(2) of 0.85 +/- 0. 05. The copper binding site shows the same degree of rigidity even though is it composed of several loops and lies outside the beta-sheet sandwich. Substantial exchange broadening was found for a number of residues surrounding the side chain of His-35. The average exchange rate has been determined from NMR exchange spectroscopy experiments and is 45 +/- 6 s(-)(1) at 41 degrees C. The exchange broadening is caused by the protonation/deprotonation equilibrium of His-35. The NMR results indicate that the two structures of azurin observed by X-ray diffraction of crystals at pH 5.5 and 9.0 [Nar, H., Messerschmidt, A., Huber, R., Van de Kamp, M., Canters, G. W. (1991) J. Mol. Biol. 221, 765-772] are present in solution and that they interconvert slowly.
authors.affiliation: Leiden Institute of Chemistry, Leiden University, Gorlaeus Laboratories, P.O. Box 9502, 2300 RA, Leiden, The Netherlands.
authors.forename: A P
authors.initials: AP
authors.lastname: Kalverda
authors.forename: M
authors.initials: M
authors.lastname: Ubbink
authors.forename: G
authors.initials: G
authors.lastname: Gilardi
authors.forename: S S
authors.initials: SS
authors.lastname: Wijmenga
authors.forename: A
authors.initials: A
authors.lastname: Crawford
authors.forename: L J
authors.initials: LJ
authors.lastname: Jeuken
authors.forename: G W
authors.initials: GW
authors.lastname: Canters
mesh_terms: D001400:Azurin / Q000737:chemistry*; D006639:Histidine / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D011487:Protein Conformation; D011522:Protons; D012996:Solutions
chemical_list: D011522:Protons; D012996:Solutions; D001400:Azurin; D006639:Histidine