Raman optical activity characterization of native and molten globule states of equine lysozyme: comparison with hen lysozyme and bovine alpha-lactalbumin.

The research investigates the structure and characteristics of equine lysozyme in its native and nonnative states using vibrational Raman optical activity (ROA) and compares it with the homologous proteins hen egg white lysozyme and bovine alpha-lactalbumin.

Introduction

• The research aims to understand the secondary and tertiary structures of equine lysozyme by using ROA spectrum, a method that enables the characterization of molecular structures and conformations.
• Comparisons are made with the homologous proteins hen egg white lysozyme and bovine alpha-lactalbumin to understand structural similarities and differences.

Findings and Analysis

• The study found that the ROA spectrum of holo equine lysozyme closely resembled that of hen lysozyme, indicating a similarity in their overall secondary and tertiary structures.
• A major finding was a strong positive ROA band at approximately 1340 cm(-1) in equine lysozyme, similar to bovine alpha-lactalbumin, suggesting a more hydrated form of alpha helix and potentially reflecting greater flexibility and calcium-binding ability in these two compared with hen lysozyme.
• The study also reveals the presence of broader bands centered at approximately 1305 cm(-1) in equine lysozyme, which points to a greater heterogeneity in parts of its alpha-helical sequences.
• Furthermore, the ROA spectrum of apo equine lysozyme, the form without calcium, is almost identical to that of the holo protein, suggesting that the backbone and side chain conformations, including the calcium-binding loop, are not greatly affected by the absence of calcium.
• Molten globule or state A forms of equine lysozyme have similar structures, containing much hydrated alpha helix, based on their ROA spectra. The state A of equine lysozyme appears more structured than that of bovine alpha-lactalbumin.
• The absence of a positive tryptophan ROA band at approximately 1551 cm(-1) in the native holo protein in the state A implies the presence of nonnative conformations of the tryptophans associated with a previously identified cluster of hydrophobic residues.

Conclusion

• The study provides valuable insights into the structural aspects of equine lysozyme, contributing to a better understanding of this protein and its function.
• The findings could have implications for further studies on protein biochemistry and have potential applications in protein design and engineering.