The Role of Crystallins in Maintaining Lens Transparency

Crystallins are adapted not to crystallise; the eye lens needs to be a highly concentrated solution, but it needs to avoid small crystals or aggregates, since they would scatter light and make the lens opaque. Our lenses achieve this by mixing together several different crystallins, which together form a uniform, glassy solution. The protein molecules are arranged in a way which means that their refractive index is nearly the same as glass- which makes the lens transparent. This is due to the small size of the protein molecules, less than 10 nm in diameter, and their close packing at high concentration

The lens contains three major types of crystallins, making up about 90% of the protein. Alpha crystallins are the most common. They are composed of two similar types of protein chain, which associate to form large spherical complexes containing about 40 chains. These large spheres repel one another and distribute themselves throughout the lens cells. Beta crystallins, shown here from, also form oligomeric complexes (contains a limited number of monomers), typically formed of two or six copies of the chain. There are several similar beta crystallins, which can mix and match to form a bunch of different types of oligomers. Finally, gamma crystallins are monomeric, and serve as a weak glue to gently bind the alpha crystallins together.

Our crystallin proteins need to last our entire life, so the lens contains a powerful method to protect them. Alpha crystallin acts as chaperone, finding damaged proteins and binding to them before they can form translucent or opaque complexes. Unfortunately, in spite of this protection, the damage builds up as we age, as crystallins are broken or unfolded or oxidized. Slowly, the damage leads to progressive build-up of opaque aggregates, leading to cataracts. 

Dendrocnide moroides aka “gympie gympie”

The Dendrocnide moroides has been said to be the plant with the most excruciating sting in the world- injuring and sometimes killing dogs, horses, and even humans. The species is relatively common in Queensland, and is native to the warm forests of northern Australia; typically growing 1.5-2 meters in height. The plant has large, thin heart-shaped leaves, which are covered in small silica-tipped hairs, which are extremely efficient at penetrating the skin of its victims. Contact with these hairs causes the release of the potent toxin moroidin, which causes the long list of agonising symptoms. One reason why the plant is extremely dangerous is that the hairs are very loosely fitted to the cuticle of the leaf, meaning that with light winds, the hairs can be blown off the plant and cause irritation if it comes into contact with an animal. On case of the sting resulted in suicide, after a man accidently used a leaf as a piece of toilet paper. The hairs of the plant can be embedded in the skin, and can remain there if no appropriate treatment has been given, which results in long-term pain and discomfort, which is one of the reasons why the plant is so feared- as the symptoms can sometimes last for weeks, if not months.

Moroidin is the active chemical in the toxin of the plant, and is a bicyclic octapeptide. Its skeletal formula is shown on the adjacent diagram, and it has a molecular formula of  C₄₇H₆₆N₁₄O_{10. It is made of 9 different amino acids.} 

The recommended treatment for skin exposed to the hairs is applying diluted hydrochloric acid and then pulling out the hairs with a hair removal strip. Tweezers or sticky tape can also be used, but care needs to be taken when removing the hairs, as if broken they will worsen the pain.