Structural Analysis of an Insect Lysozyme Exhibiting Catalytic Efficiency at Low Temperatures^,

Abstract

Bombyx mori lysozyme (BmLZ), from the silkworm, is an insect lysozyme. BmLZ has considerable activity at low temperatures and low activation energies compared with those of hen egg white lysozyme (HEWLZ), according to measurements of the temperature dependencies of relative activity (lytic and glycol chitin) and the estimation of activation energies using the Arrhenius equation. Being so active at low temperatures and low activation energies is characteristic of psychrophilic (cold-adapted) enzymes. The three-dimensional structure of BmLZ has been determined by X-ray crystallography at 2.5 A resolution. The core structure of BmLZ is similar to that of c-type lysozymes. However, BmLZ shows some distinct differences in the two exposed loops and the C-terminal region. A detailed comparison of BmLZ and HEWLZ suggests structural rationalizations for the differences in the catalytic efficiency, stability, and mode of activity between these two lysozymes.

Recombinant Bacterial Expression of the Lysozyme from the Tobacco-Hornworm Manduca sexta with Activity at Low Temperatures

“…Most cold-adapted enzymes come from psychrophilic bacteria and are characterized by a high specific enzymatic activity in the range of 0-30°C (Gerday et al 2000). In this work we found that the optimal temperature for Ms-lyz was 15°C lower than that of hen egg white lysozyme, as previously reported for the coldadapted silkworm lysozyme (Matsuura et al 2002). Also, the specific activity of Ms-lyz was about twice that of hen egg white lysozyme at 5°C as reported for cold adapted enzymes ( Figure 3).…”

“…Hen egg white lysozyme has been expressed in eukaryotic systems such as Aspergillus (Archer et al 1990), and yeast (Nakamura et al 1993), and the insect lysozyme from Bombyx mori was expressed in Picha pastoris (Matsuura et al 2002). However, bacterial expression of lysozyme is not trivial due to the problems with protein refolding.…”

“…The lysozyme from hen egg white has been overexpressed in several heterologous systems , Koshiba et al 1999. Insect lysozymes can maintain their enzymatic activity at low temperatures (Matsuura et al 2002) which is desirable for an antibacterial when used in food processing. Moreover, it is possible to study the nature of the lysozyme antibacterial activity at low temperatures by expression of site-directed mutants.…”

Extreme Catalysts from Low-Temperature Environments

“…In addition to mutational studies, the involvement of these factors in protein adaptation is suggested from comparative studies between psychrophilic enzymes and their heat-stable homologues based on homology models and 3D structures. An increased number of crystallographic structures of psychrophilic enzymes from bacteria and cold-adapted fishes have been previously elucidated (29)(30)(31)(32)(33)(34)(35)(36)(37)(38)(39)(40)(41) (29) and fish trypsin (37). Other structures should become available soon, as crystals of three other cold-active enzymes have been obtained (43)(44)(45).…”

Cloning and overexpression of lysozyme fromSpodoptera liturain prokaryotic system

“…Together with a variety of potent antibacterial and antifungal peptides, insect lysozyme is induced and secreted into the blood (hemolymph), which becomes a hostile environment for bacterial growth (Hultmark 1996). Insect lysozyme is generally considered as a basic, heat-stable, and cationic protein, and has been studied for structural and functional stability for the past decades (Matsuura et al 2002).…”