SAXS structure of homodimeric oxyHemoglobin III from bivalve Lucina pectinata

Biopolymers. 2021 Jun;112(6):e23427. doi: 10.1002/bip.23427. Epub 2021 Apr 1.


Hemoglobin III (HbIII) is one of the two oxygen reactive hemoproteins present in the bivalve, Lucina pectinata. The clam inhabits a sulfur-rich environment and HbIII is the only hemoprotein present in the system which does not yet have a structure described elsewhere. It is known that HbIII exists as a heterodimer with hemoglobin II (HbII) to generate the stable Oxy(HbII-HbIII) complex but it remains unknown if HbIII can form a homodimeric species. Here, a new chromatographic methodology to separate OxyHbIII from the HbII-HbIII dimer has been developed, employing a fast performance liquid chromatography and ionic exchange chromatography column. The nature of OxyHbIII in solution at concentrations from 1.6 mg/mL to 20.4 mg/mL was studied using small angle X-ray scattering (SAXS). The results show that at all concentrations, the Oxy(HbIII-HbIII) dimer dominates in solution. However, as the concentration increases to nonphysiological values, 20.4 mg/mL, HbIII forms a 30% tetrameric fraction. Thus, there is a direct relationship between the Oxy(HbIII-HbIII) oligomeric form and hemoglobin concentration. We suggest it is likely that the OxyHbIII dimer contributes to active oxygen transport in tissues of L pectinata, where the Oxy(HbII-HbIII) complex is not present.

Keywords: SAXS; hemeproteins; protein oligomerization.

MeSH terms

  • Amino Acid Sequence
  • Animals
  • Bivalvia / genetics
  • Bivalvia / metabolism*
  • Crystallography, X-Ray
  • Electrophoresis, Polyacrylamide Gel
  • Heme / chemistry
  • Heme / metabolism
  • Hydrogen Sulfide / metabolism
  • Oxyhemoglobins / chemistry*
  • Oxyhemoglobins / genetics
  • Oxyhemoglobins / metabolism
  • Protein Conformation
  • Protein Multimerization*
  • Scattering, Small Angle*
  • Sequence Homology, Amino Acid
  • Tandem Mass Spectrometry / methods
  • X-Ray Diffraction / methods*


  • Oxyhemoglobins
  • Heme
  • Hydrogen Sulfide