title: Urea-induced unfolding of Glossoscolex paulistus hemoglobin, in oxy- and cyanomet-forms: a dissociation model.
abstract: The urea effect on the giant extracellular hemoglobin of Glossoscolex paulistus (HbGp) stability was studied by analytical ultracentrifugation (AUC) and small angle X-ray scattering (SAXS). AUC data show that the sedimentation coefficient distributions curves c (S), at 1.0 mol/L of urea, display a single peak at 57 S, associated to the undissociated protein. The increase in urea concentration, up to 4.0 mol/L, induces the appearance of smaller species, due to oligomeric dissociation. The sedimentation coefficients and molecular masses are 9.2S and 204 kDa for the dodecamer (abcd)(3), 5.5S and 69 kDa for the tetramer (abcd), 4.1S and 52 kDa for the trimer (abc) and 2.0 S and 17 kDa for the monomer d, respectively. SAXS data show initially a decrease in the I(0) values due to the oligomeric dissociation, and then, above 4.0 mol/L of denaturant, for oxy-HbGp, and above 6.0 mol/L for cyanomet-HbGp, an increase in the maximum dimension and gyration radius is observed, due to the unfolding process. According to AUC and SAXS data the HbGp unfolding is described by two phases: the first one, at low urea concentration, below 4.0 mol/L, characterizes the oligomeric dissociation, while the second one, at higher urea concentration, is associated to the unfolding of dissociated species. Our results are complementary to a recent report based on spectroscopic observations.
authors.affiliation: Instituto de Química de São Carlos, Universidade de São Paulo, SP, Brazil.
authors.forename: Francisco A O
authors.initials: FA
authors.lastname: Carvalho
authors.forename: José Wilson P
authors.initials: JW
authors.lastname: Carvalho
authors.forename: Patrícia S
authors.initials: PS
authors.lastname: Santiago
authors.forename: Marcel
authors.initials: M
authors.lastname: Tabak
mesh_terms: D000818:Animals; D006454:Hemoglobins / Q000737:chemistry*; D008956:Models, Chemical; D009835:Oligochaeta / Q000737:chemistry*; D017510:Protein Folding; D014508:Urea / Q000737:chemistry*
chemical_list: D006454:Hemoglobins; D014508:Urea