Structural studies on prolyl hydroxylase. Conformation from circular dichroism spectroscopy

Area of Science:

• Biochemistry
• Structural Biology
• Enzymology

Background:

• Prolyl hydroxylase (EC 1.14.11.12) is an enzyme critical for collagen synthesis.
• Understanding its structure is key to elucidating its function and regulation.
• Circular dichroism (CD) spectroscopy is a powerful tool for analyzing protein secondary structure.

Purpose of the Study:

• To determine the secondary structure of purified prolyl hydroxylase using CD spectroscopy.
• To investigate the impact of heat denaturation on the enzyme's structure and activity.
• To correlate structural changes with loss of enzyme function.

Main Methods:

• Circular dichroism (CD) spectroscopy was employed to analyze the native and heat-denatured states of prolyl hydroxylase at pH 7.8.
• Far-UV CD spectra were used to estimate secondary structure content (alpha-helix, beta-structure, random coil).
• Near-UV CD spectra provided information on the environment of aromatic residues (phenylalanine, tyrosine, tryptophan).

Main Results:

• The native enzyme exhibited an estimated secondary structure composition of 40% alpha-helix, 40% beta-structure, and 20% random coil.
• Near-UV CD spectra showed distinct negative dichroic bands in the native enzyme, indicative of aromatic residues in an asymmetric environment.
• These near-UV bands disappeared upon heat denaturation, and the denaturation profiles for helical content loss and enzyme activity loss were coincident.

Conclusions:

• Prolyl hydroxylase possesses a significant degree of ordered secondary structure, including substantial alpha-helical content.
• Heat denaturation leads to loss of secondary structure and enzyme activity.
• The study strongly suggests that the alpha-helical segments of prolyl hydroxylase are essential for its catalytic activity.