Circular dichroism of porcine, bovine, and equine pancreatic phospholipases A2 and their zymogens. Unusual conformations simulating helix content.

This research article investigates the conformation of pancreatic phospholipases A2 from porcine, bovine, and equine sources and their zymogens through a circular dichroism (CD) probe, discovering that these structures share moderate amounts of α-helical conformation and unusual conformations that simulate helix content.

Methodology and Structural Analyses

• Researchers used circular dichroism (CD) probes in both far and near ultraviolet spectral zones to analyze conformations of pancreatic phospholipases A2 derived from porcine, bovine, and equine sources, as well as their respective zymogens.
• These studies detected CD curves that indicated the presence of a moderate amount of α-helical conformation in all the phospholipases and their zymogens.
• However, based on the known primary structure and recent X-ray structural analyses, the researchers concluded that the positive CD bands at 190–191 nm and the negative bands at 208–210 nm and 222–225 nm are caused not only by α-helices but also by other asymmetrical structures, possibly rings including disulfide bonds.

Conformational Stability

• The main chain conformation of the phospholipases and their zymogens was found to be highly resistant to acid, thus demonstrating structural stability.
• However, the conformational structure was sensitive to sodium dodecyl sulfate in acidic solutions, and, to some extent, alkali.
• The researchers determined that the stability of the proteins’ macromolecules depended largely on disulfide bonds and hydrophobic interactions, based on observed CD changes in the presence of perturbants.

Tertiary Structure Differences

• The CD spectra in the near ultraviolet zone showed that the differences between the enzymes and their zymogens, with regard to tertiary structure, were very small.
• It was observed that the tertiary structure of the horse phospholipase deviated from the porcine and bovine phospholipases. This difference could suggest species-specific variances in the tertiary structure of these enzymes.
• The researchers also found all the enzymes and zymogens’ tertiary structures to be highly sensitive to sodium dodecyl sulfate – a notable characteristic of these proteins.