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Conformational changes in oxyhemoglobin C (Glu beta 6-->Lys) detected by spectroscopic probing
R E Hirsch1, M J Lin, G J Vidugiris
1Department of Medicine, Montefiore Medical Center, Bronx, New York, USA.
Insights
Hemoglobin C (HbC) crystals form readily due to a weakened Trp beta 15-Ser beta 72 hydrogen bond. This structural change likely causes the A helix to move away from the E helix in oxyHbC.
Area of Science:
- Biochemistry
- Molecular Biology
- Structural Biology
Background:
- Hemoglobin C (HbC) and Hemoglobin S (HbS) share a mutation site but exhibit different polymerization/crystallization behaviors.
- Deoxyhemoglobin S (deoxyHbS) polymerizes, while oxyhemoglobin C (oxyHbC) readily forms crystals.
- The molecular basis for oxyHbC's crystallization propensity remains unclear due to a lack of detailed structural data.
Purpose of the Study:
- To investigate potential solution-phase conformational changes in HbC compared to normal adult hemoglobin (HbA).
- To elucidate the molecular mechanism underlying oxyHbC's propensity to form crystals.
Main Methods:
- Utilized intrinsic fluorescence spectroscopy.
- Employed UV resonance Raman spectroscopy.
- Compared spectroscopic data of HbC with HbA.
Main Results:
- Spectroscopic data revealed a weakening of the critical Trp beta 15-Ser beta 72 hydrogen bond in HbC.
- This hydrogen bond alteration is proposed to cause a conformational shift, displacing the A helix from the E helix.
Conclusions:
- The identified structural changes in HbC provide a molecular explanation for its distinct crystallization behavior.
- Weakening of the Trp beta 15-Ser beta 72 hydrogen bond is a key factor in oxyHbC's propensity to form crystals.
Abstract:
Hemoglobin C (Glu beta 6-->Lys) shares with hemoglobin S (Glu beta 6-->Val) the site of mutation, but with different consequences: deoxyHbS forms polymers, whereas oxyHbC readily forms crystals. The molecular mechanism for this property of oxyHbC is unknown. Since no detailed oxyHbC crystal structural information exists, spectroscopic probing is used in this study to investigate possible solution-phase conformational changes in HbC compared with HbA. Intrinsic fluorescence combined with UV resonance Raman data demonstrate a weakening of the Trp beta 15-Ser beta 72 hydrogen bond that most likely leads to a displacement of the A helix away from the E helix.