Structure of Muramidase (Lysozyme)

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Abstract
Previously, it has been concluded that the muramidase molecule consists of α-helica portion and internal fold and that the internal fold assumes intramolecular cross-β configuration and is stabilized by hydrophobic interactions. In order to substantiate the structure of the internal fold of the muramidase molecule, the hydrodynamic, optical rotatory, and spectral properties of muramidase in DMSC water mixtures were studied. Muramidase molecule has a configuration of greater flexibility in DMSO, while the molecular weight remains unchanged. Infrared absorption spectral data show the presence of β-structure as well as α-helix and disordered structure in the muramidase molecule in D2O solution. In DMSO solution, or the other hand, the presence of β-structure was not detected. Thus, DMSO destroy mainly the β-structure in the muramidase molecule. The change in the optical rotatory properties of muramidase with the solvent composition in DMSO-water mixtures is also interpreted as the result of the disruption of β-structure. As inferred from the ultraviolet absorption spectra, the disruption of β-structure accompanies the exposure of tryptophan residues which have been buried in the internal fold. These facts suggest that the internal fold assumes β-structure. Previously, it was found that the presence of some organic solvents such as methanol, ethanol, or 2-chloroethanol increased only the value of −a0 leaving the value of −b0 unchanged. This fact can be also interpreted as the result of the disruption of cross-β structure. It is also suggested that the refractive index at 546mμ of the internal fold is not far from 1.440.

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