title: Guanidine hydrochloride and urea effects upon thermal stability of Glossoscolex paulistus hemoglobin (HbGp).
abstract: Glossoscolex paulistus hemoglobin (HbGp) has a molecular mass of 3600kDa. It belongs to the hexagonal bilayer hemoglobin class, which consists of highly cooperative respiratory macromolecules found in mollusks and annelids. The present work focusses on oxy-HbGp thermal stability, in the presence of urea and guanidine hydrochloride (GuHCl), monitored by several techniques. Initially, dynamic light scattering data show that the presence of GuHCl induces the protein oligomeric dissociation, followed by a significant 11-fold increase in the hydrodynamic diameter (DH) values, due to the formation of protein aggregates in solution. In contrast, urea promotes the HbGp oligomeric dissociation, followed by unfolding process at high temperatures, without aggregation. Circular dichroism data show that unfolding critical temperature (Tc) of oxy-HbGp decreases from 57°C, at 0.0 mol/L of the denaturant, to 45°C, in the presence of 3.5 mol/L of urea, suggesting the reduction of HbGp oligomeric stability. Moreover, differential scanning calorimetry results show that at lower GuHCl concentrations, some thermal stabilization of the hemoglobin is observed, whereas at higher concentrations, the reduction of stability takes place. Besides, HbGp is more stable in the presence of urea when compared with the guanidine effect, as deduced from the differences in the concentration range of denaturants.
authors.affiliation: Instituto de Química de São Carlos-Universidade de São Paulo, Brazil. Electronic address: adrianocarbureto@gmail.com.
authors.forename: Francisco A O
authors.initials: FA
authors.lastname: Carvalho
authors.affiliation: Instituto de Química de São Carlos-Universidade de São Paulo, Brazil.
authors.forename: Fernanda R
authors.initials: FR
authors.lastname: Alves
authors.affiliation: Instituto de Química de São Carlos-Universidade de São Paulo, Brazil; Universidade do Estado de Mato Grosso, MT, Brazil.
authors.forename: José W P
authors.initials: JW
authors.lastname: Carvalho
authors.affiliation: Instituto de Química de São Carlos-Universidade de São Paulo, Brazil.
authors.forename: Marcel
authors.initials: M
authors.lastname: Tabak
mesh_terms: D000818:Animals; D000845:Annelida; D002152:Calorimetry, Differential Scanning; D002942:Circular Dichroism; D019791:Guanidine / Q000494:pharmacology*; D006454:Hemoglobins / Q000737:chemistry*; D008958:Models, Molecular; D011487:Protein Conformation / Q000187:drug effects; D055503:Protein Multimerization; D058849:Protein Refolding; D055550:Protein Stability / Q000187:drug effects*; D058767:Protein Unfolding; D013816:Thermodynamics; D014508:Urea / Q000494:pharmacology*
chemical_list: D006454:Hemoglobins; D014508:Urea; D019791:Guanidine
keywords: Aggregation; Dynamic light scattering; Glossoscolex paulistus hemoglobin; Guanidine hydrochloride; Unfolding process.; Urea