My sweet and strong protein❤ lysozyme
the strong yet sweet protein that protects us
Lysozyme (pronounced lai· suh· zaim) might not be a familiar word for many. It is however a protein, an enzyme, quite present in our lives. It is one of the strongest defence mechanisms our body has. It is swimming in our tears and in our saliva, in mother’s milk to protect infants form gut infections and in the amniotic fluid. I even just saw it written on my medication for sorethroat!
What does lysozyme do?
Lysozyme is a small protein that attacks bacteria and breaks down one of their crucial structures, the membrane that holds them together. In particular, it cleaves the β-1,4-glycosidic bond between N-acetylmuramic acid and N-acetylglucosamine of peptidoglycan. Made of sugars and crosslinked peptides, peptidoglycan gives structure and confers structural integrity to bacteria. It degrades (hydrolyses) peptidoglycan, the building block of bacterial cell-wall. Being able to attack one of the components present in all bacteria, it is a powerful weapon not only in medicine but also for biotech applications.
Hey you lysozyme, what are you doing there?
The 100th year anniversary of the discovery is coming soon and we now have characterised at the gene and protein level the human lysozyme. It is a 148-amino-acids long that include a short initial sequence driving it outside the cell, where it exerts its bactericidal function, i.e. in mucus, milk, and tears. Human lysozyme share the sequence with chimpanzee and bonobos at a 100% and a 98–99% with gorillas. The most commonly used is however isolated from the white of chicken eggs and can be purchased for a few euros/dollars a gram.
Lysozyme forms crystals easily
Lysozyme molecules tend to aggregate into ordered structures, crystals, easily and under different conditions. Crystals can have different shapes, even rods or needles. Considering the costs of the purified lysozyme, its crystallisation is an experiment that can be carried out at home, without the need of special instruments.
Innovations with lysozyme
The natural function of lysozyme is to kill bacteria. Effective in fighting lactic acid bacteria, it is sometimes added to wine to prevent spoilage and to cheese to avoid off-flavours due to undesired contamination. It showed effective even in preserving cosmetics. Lysozyme is also a valid alternative to antibiotics in animal feed of pigs, in particular.
Smart materials take often advantage of biological tools. Materials with antibacterial activity have a high potential in various fields, not only medicine but also packaging. Entrapped in a structure made of pectin and cellulose, a thin film with antibacterial activity can be assembled. By changing the polymeric materials, an innovative gauze for wound treatment can be prepared. For example, using agarose to make a gel and sericin, the protein of silk.
Lysozyme is a very small molecule and it can aso be used to prepare sensors as small as 1 nm, that is some 50'000 times smaller than one of your . When gold nanoparticles are included in a lysozyme molecule, we obtain a stable and soluble fluorecsent assembly whose fluorescence is switched off in the presence of mercury. A lysozyme-based nanosensor for mercury!
Lysozyme is sweet ❤
We always think of sugars when thinking of sweet molecules. You might be thus surprised to know that also some proteins are sweet! We drop crystals of sucrose in our coffee and tea and cakes, how about putting some protein instead’ Especially now that protein-rich diets are on fashion, sweet proteins can hold a secret.
Lysozyme itself is almost 1'000-folds sweeter than regular sugar whereas another protein, thaumatin, is one of the sweetest with a 2'000-folds higher sweetness but with only 4 kcal/g. For us to feel a sweet taste, specific receptors on out tongue have to be triggered. Thanks to its structure lysozyme can interact with these sensors in our tongue and specific for sweetness, i.e. the dimeric T1R2-T1R3 sweet receptor. The presence of specific chemical groups on its surface are crucial for the sweet taste. Studies have shown how the positive charges on the surface of the lysozyme molecule are responsible for its sweetness and they can be changed to tune the taste.
The protein world is rich and always full of surprises.
