title: Quaternary structure heterogeneity of oligomeric proteins: a SAXS and SANS study of the dissociation products of Octopus vulgaris hemocyanin.
abstract: Octopus vulgaris hemocyanin shows a particular self-assembling pattern, characterized by a hierarchical organization of monomers. The highest molecular weight aggregate is a decamer, the stability of which in solution depends on several parameters. Different pH values, buffer compositions, H₂O/D₂O ratios and Hofmeister's salts result in modifications of the aggregation state of Octopus vulgaris hemocyanin. The new QUAFIT method, recently applied to derive the structure of the decameric and the monomeric assembly from small-angle scattering data, is used here to model the polydisperse system that results from changing the solution conditions. A dataset of small-angle X-rays and neutron scattering curves is analysed by QUAFIT to derive structure, composition and concentration of different assemblies present in solution. According to the hierarchy of the association/dissociation processes and the possible number of different aggregation products in solution, each sample has been considered as a heterogeneous mixture composed of the entire decamer, the dissociated "loose" monomer and all the intermediate dissociation products. Scattering curves corresponding to given experimental conditions are well fitted by using a linear combination of single particle form factors. QUAFIT has proved to be a method of general validity to describe solutions of proteins that, even after purification processes, result to be intrinsically heterogeneous.
authors.affiliation: Department of Life and Environmental Sciences, Marche Polytechnic University and CNISM, Ancona, Italy. f.spinozzi@univpm.it
authors.forename: Francesco
authors.initials: F
authors.lastname: Spinozzi
authors.forename: Paolo
authors.initials: P
authors.lastname: Mariani
authors.forename: Ivan
authors.initials: I
authors.lastname: Mičetić
authors.forename: Claudio
authors.initials: C
authors.lastname: Ferrero
authors.forename: Diego
authors.initials: D
authors.lastname: Pontoni
authors.forename: Mariano
authors.initials: M
authors.lastname: Beltramini
mesh_terms: D000818:Animals; D002021:Buffers; D006433:Hemocyanins / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D008958:Models, Molecular; D033363:Neutron Diffraction; D049831:Octopodiformes / Q000737:chemistry; D011485:Protein Binding; D055503:Protein Multimerization; D020836:Protein Structure, Quaternary; D053838:Scattering, Small Angle; D014961:X-Ray Diffraction
chemical_list: D002021:Buffers; D006433:Hemocyanins