Comparison of solution and crystalline state protein structures. Photoacoustic study of horse and human hemoglobins.

The study examines the impact of crystallization on protein conformations by analyzing the optical absorption spectra of crystalline state hemoglobin derivatives. The results show that there is a high similarity in the protein conformations in solution and crystalline states and crystallization doesn’t alter the absorption properties of specific hemoglobin derivatives.

Methodology

• The research team had chosen hemoglobin derivatives as the proteins to study. Optical absorption spectra of these proteins’ crystalline state were examined.
• The spectra were procured from photoacoustic spectra with the aid of a computer-assisted analysis.
• By employing crystal minus solution state difference spectra, a comparison was made between crystal and solution state hemoglobins to assess their structural similarities.

Results & Implications

• The study established that the conformations of these proteins remain analogous in both states – crystal and solution.
• Crystallization does not affect the absorption properties of horse oxyhemoglobin or the cyanide and azide adducts of horse and human methemoglobin, reinforcing the structural consistency observed.
• Spectra from crystalline methemoglobins, prepared via ligand exchange in the crystalline state, were found identical to those from the final crystalline state adduct prepared without ligand exchange.
• The allosteric effector, inositol hexaphosphate, was observed to cause the same spectral changes in both solution and crystalline state hemoglobins, complementing the findings above.
• However, differences were observed in crystal and solution state spectra of both fluoride and aquo methemoglobin; these differences suggest that crystallization might cause minor but potentially functionally significant changes in the heme regions of these derivatives.

Conclusion

• Despite the observed changes in fluoride and aquo methemoglobin, the majority of the findings suggested a high degree of similarity across crystalline and solution states of the studied proteins.
• The study emphasizes the insight crystallization provides into protein structures, specifically hemoglobin derivatives, and supports further investigations to understand the implications of crystallization on protein conformations.