title: Structure, conformational stability, and enzymatic properties of acylphosphatase from the hyperthermophile Sulfolobus solfataricus.
abstract: The structure of AcP from the hyperthermophilic archaeon Sulfolobus solfataricus has been determined by (1)H-NMR spectroscopy and X-ray crystallography. Solution and crystal structures (1.27 A resolution, R-factor 13.7%) were obtained on the full-length protein and on an N-truncated form lacking the first 12 residues, respectively. The overall Sso AcP fold, starting at residue 13, displays the same betaalphabetabetaalphabeta topology previously described for other members of the AcP family from mesophilic sources. The unstructured N-terminal tail may be crucial for the unusual aggregation mechanism of Sso AcP previously reported. Sso AcP catalytic activity is reduced at room temperature but rises at its working temperature to values comparable to those displayed by its mesophilic counterparts at 25-37 degrees C. Such a reduced activity can result from protein rigidity and from the active site stiffening due the presence of a salt bridge between the C-terminal carboxylate and the active site arginine. Sso AcP is characterized by a melting temperature, Tm, of 100.8 degrees C and an unfolding free energy, DeltaG(U-F)H2O, at 28 degrees C and 81 degrees C of 48.7 and 20.6 kJ mol(-1), respectively. The kinetic and structural data indicate that mesophilic and hyperthermophilic AcP's display similar enzymatic activities and conformational stabilities at their working conditions. Structural analysis of the factor responsible for Sso AcP thermostability with respect to mesophilic AcP's revealed the importance of a ion pair network stabilizing particularly the beta-sheet and the loop connecting the fourth and fifth strands, together with increased density packing, loop shortening and a higher alpha-helical propensity.
authors.affiliation: Dipartimento di Scienze e Tecnologie Biomediche, Università di Udine, Udine, Italy.
authors.forename: Alessandra
authors.initials: A
authors.lastname: Corazza
authors.forename: Camillo
authors.initials: C
authors.lastname: Rosano
authors.forename: Katiuscia
authors.initials: K
authors.lastname: Pagano
authors.forename: Vera
authors.initials: V
authors.lastname: Alverdi
authors.forename: Gennaro
authors.initials: G
authors.lastname: Esposito
authors.forename: Cristina
authors.initials: C
authors.lastname: Capanni
authors.forename: Francesco
authors.initials: F
authors.lastname: Bemporad
authors.forename: Georgia
authors.initials: G
authors.lastname: Plakoutsi
authors.forename: Massimo
authors.initials: M
authors.lastname: Stefani
authors.forename: Fabrizio
authors.initials: F
authors.lastname: Chiti
authors.forename: Simone
authors.initials: S
authors.lastname: Zuccotti
authors.forename: Martino
authors.initials: M
authors.lastname: Bolognesi
authors.forename: Paolo
authors.initials: P
authors.lastname: Viglino
mesh_terms: D017766:Acid Anhydride Hydrolases / Q000737:chemistry* / Q000378:metabolism; D019843:Archaeal Proteins / Q000737:chemistry / Q000378:metabolism; D004795:Enzyme Stability; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D011487:Protein Conformation; D012542:Scattering, Radiation; D016944:Sulfolobus / Q000201:enzymology*; D013816:Thermodynamics; D000097024:Acylphosphatase
chemical_list: D017766:Acid Anhydride Hydrolases; D019843:Archaeal Proteins; D000097024:Acylphosphatase