title: Thermal aggregation and ion-induced cold-gelation of bovine serum albumin.
abstract: Protein cold-gelation has recently received particular attention for its relevance in bio and food technology. In this work, we report a study on bovine serum albumin cold-gelation induced by copper or zinc ions. Metal-induced cold-gelation of proteins requires two steps: during the first one, the heat treatment causes protein partial unfolding and aggregation; then, after cooling the solution to room temperature, gels are formed upon the addition of metal ions. The thermally induced behaviour has been mainly investigated through different techniques: Fourier transform infrared (FTIR) spectroscopy, circular dichroism, dynamic light scattering (DLS) and rheology. Data have shown that the aggregation process is mainly due to protein conformational changes--alpha-helices into beta-aggregates-forming small aggregated structures with a mean diameter of about 20 nm a few minutes after heating. After metal ion addition, the viscoelastic properties of the gels have been investigated by rheological measurements. The behaviour of the elastic and viscous moduli as a function of time is discussed in terms of ion concentration and type. Our results show that: (1) the elastic behaviour depends on ion concentration and (2) at a given ion concentration, gels obtained in the presence of zinc exhibit an elastic value larger than that observed in the Cu(2+) case. Data suggest that cold-gelation is the result of different mechanisms: the ion-mediated protein-protein interaction and the bridging effect due to the presence of divalent ions in solution.
authors.affiliation: Consiglio Nazionale delle Ricerche, Istituto di Biofisica, U. O. di Palermo, Via U. La Malfa 153, 90146, Palermo, Italy.
authors.forename: Giovanna
authors.initials: G
authors.lastname: Navarra
authors.forename: Daniela
authors.initials: D
authors.lastname: Giacomazza
authors.forename: Maurizio
authors.initials: M
authors.lastname: Leone
authors.forename: Fabio
authors.initials: F
authors.lastname: Librizzi
authors.forename: Valeria
authors.initials: V
authors.lastname: Militello
authors.forename: Pier Luigi
authors.initials: PL
authors.lastname: San Biagio
mesh_terms: D000818:Animals; D002417:Cattle; D002942:Circular Dichroism; D003300:Copper / Q000737:chemistry*; D004548:Elasticity; D007700:Kinetics; D008027:Light; D017510:Protein Folding; D017433:Protein Structure, Secondary; D012212:Rheology; D012542:Scattering, Radiation; D012710:Serum Albumin, Bovine / Q000737:chemistry*; D017550:Spectroscopy, Fourier Transform Infrared; D013696:Temperature; D013997:Time Factors; D015032:Zinc / Q000737:chemistry*
chemical_list: D012710:Serum Albumin, Bovine; D003300:Copper; D015032:Zinc