Sodium dodecyl sulfate (SDS) effect on the thermal stability of oxy-HbGp: Dynamic light scattering (DLS) and small angle X-ray scattering (SAXS) studies

• HbGp is a multi-subunit oligomeric hemoglobin, with a high molecular mass of 3.6 MDa.
• HbGp-SDS interaction leads to complete protein oligomeric dissociation, at pH 7.0.
• Oxy-HbGp SDS-induced thermal aggregation depends on protein concentration and pH.
• HbGp-SDS interaction at pH 5.0 is characterized by aggregation at lower temperatures.
• At alkaline pH 9.0 only oligomeric dissociation is observed in oxy-HbGp-SDS system.

Glossoscolex paulistus (HbGp) hemoglobin is an oligomeric protein, presenting a quaternary structure constituted by 144 globin and 36 non-globin chains (named linkers) with a total molecular mass of 3.6 MDa. SDS effects on the oxy-HbGp thermal stability were studied, by DLS and SAXS, at pH 5.0, 7.0 and 9.0. DLS and SAXS data show that the SDS-oxy-HbGp interactions induce a significant decrease of the protein thermal stability, with the formation of larger aggregates, at pH 5.0. At pH 7.0, oxy-HbGp undergoes complete oligomeric dissociation, with increase of temperature, in the presence of SDS. Besides, oxy-HbGp 3.0 mg/mL, pH 7.0, in the presence of SDS, has the oligomeric dissociation process reduced as compared to 0.5 mg/mL of protein. At pH 9.0, oxy-HbGp starts to dissociate at 20 °C, and the protein is totally dissociated at 50 °C. The thermal dissociation kinetic data show that oxy-HbGp oligomeric dissociation at pH 7.0, in the presence of SDS, is strongly dependent on the protein concentration. At 0.5 mg/mL of protein, the oligomeric dissociation is complete and fast at 40 and 42 °C, with kinetic constants of (2.1 ± 0.2) × 10−4 and (5.5 ± 0.4) × 10−4 s−1, respectively, at 0.6 mmol/L SDS. However, at 3.0 mg/mL, the oligomeric dissociation process starts at 46 °C, and only partial dissociation, accompanied by aggregates formation is observed. Moreover, our data show, for the first time, that, for 3.0 mg/mL of protein, the oligomeric dissociation, denaturation and aggregation phenomena occur simultaneously, in the presence of SDS. Our present results on the surfactant–HbGp interactions and the protein thermal unfolding process correspond to a step forward in the understanding of SDS effects.

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