Bovine luteinizing hormone. Circular dichroism and thermal difference spectra

Area of Science:

• Biochemistry
• Structural Biology
• Hormone Research

Background:

• Luteinizing hormone (LH) is a glycoprotein hormone crucial for reproductive functions.
• Understanding the secondary and tertiary structure of LH is vital for elucidating its biological activity.
• Circular dichroism (CD) spectroscopy is a powerful tool for analyzing protein secondary structure and conformational changes.

Purpose of the Study:

• To investigate the conformational properties of bovine luteinizing hormone (bLH) using circular dichroism.
• To examine the influence of pH, reduction, and denaturation on bLH structure.
• To assess the contribution of disulfide bonds and tyrosine residues to the hormone's ellipticity.

Main Methods:

• Far-UV (200-240 nm) and near-UV (240-320 nm) circular dichroism spectroscopy.
• Chemical denaturation and reduction of the hormone.
• Thermal perturbation difference spectroscopy.
• Comparison with denatured and reduced ribonuclease and insulin.

Main Results:

• Disulfide groups do not significantly contribute to side-chain ellipticity in bLH.
• Subunit dissociation without unfolding reversibly decreases near-UV ellipticity.
• Two tyrosine residues are located at the subunit interface and are inaccessible to water.
• Only a subset of accessible tyrosine residues are reactive to N-acetylimidazole.

Conclusions:

• The study provides insights into the structural dynamics and stability of bovine luteinizing hormone.
• Conformational changes associated with subunit interactions and tyrosine residue environments were characterized.
• These findings contribute to a deeper understanding of LH structure-function relationships.