Lysozyme is an enzyme found in most cells and protects them by dissolving polysaccharide components of certain bacterial cell walls. This enzyme was first discovered by Alexander Fleming in 1922. Having a cold, he dripped a small amount of mucus on a bacteria culture plate. He then observed a dissolving of the bacteria where he had dripped mucus. Upon discovering the enzymatic nature of this molecule, he named it lysozyme: lyso- due to its lysing capabilities and -zyme because it was an enzyme.
The 3-D structure of lysozyme was first determined by David Phillips in 1965. Click here to view a RasMol image of lysozyme. Phillips and his colleagues used high-resolution electron density mapping to first visualize the enzyme. It is relatively small (14.6 kd), but highly stable, due to four disulfide cross-linkages (shown in yellow in the RasMol image). The protein consists several a-helices andB-sheets and is characterized by a highly nonpolar interior.
This enzyme acts by hydrolysing a glycosidic bond between two sugars of the bacterial cell wall. These two sugars are N-acetylmuramate (NAM) and N-acetylglucosamine (NAG), and they are joined by a B-(1-4)-Glycosidic bond. Lysozyme only hydrolyses the bond between the C-1 of NAM and C-4 of NAG, thus the sugars must be joined in this order (NAM-NAG).
Since lysozyme acts as a cellular defense mechanism against bacterial invaders, one would expect this enzyme to be conserved over a wide range of organisms. Below are five different organisms in which the lysozyme gene has been cloned. Beside each organism is a link to a GenBank data sheet, with the cDNA sequence and/or lysozyme translation sequence used highlighted in bold.
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