Salient

Nanomachines and glycoproteins

By Matthew Proctor | 26 May, 2008

Benjamin Matthewson is doing his PhD thesis on the formation of calcium carbonate in kina shells. When calcium carbonate is formed in the lab, it forms a rhomboid, but when formed in the presence of a mixture of glycoproteins (macromolecules with both protein and sugar parts) found in shellfish, it forms intricate patterns of microscopic spikes which cannot be created artificially.

The process of isolating the glycoproteins is complicated. The spines of kina are first crushed and dissolved, then blended to form a fine green paste. This paste then undergoes a process of repeated filtering to derive just a few hundred micrograms of glycoprotein mixture. When this mixture is added to a calcium carbonate solution it crystallises in microscopic spikes.

The next part of his research is to try to identify what conditions are necessary for the crystals to form in this way. He has shown that both the protein and the sugar are necessary, but insufficient, for the correct formation of calcium carbonate. Although he has not yet tested it, he suspects that a mixture of the sugar and the protein, but not chemically bound into a glycoprotein, would not function correctly either. Matthewson has found that scientists often rely upon reductionist logic, and fail to understand that a glycoprotein is not just a protein plus a sugar; the two need to be together.

The protein part of the glycoprotein has a region that is strongly acidic (negatively charged). The most acidic proteins known to man have been discovered in shellfish. Matthewson has observed that parts of the protein section can be cut away, and the glycoprotein will still function effectively, unless the acidic region of the protein is damaged, in which case it will not work.

Another function of his research has been to characterise some of the sugars associated with the glycoproteins in kina. This is uncharted territory, as most research to date has been on the proteins. Matthewson degrades the glycoproteins in different ways, observing how removing certain areas of the sugars affects the growth of calcium carbonate crystals.

This area of nanotechnology has not received much scientific attention. Research has been conducted upon the glycoproteins present in paua. Paua only contains three different glycoproteins, but there are many present in kina; it’s unclear how many. Because they are all very large molecules, with minute differences, separating them to analyse their individual effects is extremely difficult. At a recent conference in the States, Matthewson was amazed to discover how much one team had discovered about a particular protein. He later learnt that the team had been working on that single protein for the last 20 years.

The process is not well understood. It was initially thought that the glycoproteins were simply inhibiting the calcium carbonate forming in certain areas, but allowing it to form around these areas. The process has been found to be more complicated than that. Japanese researchers on paua discovered that the negatively charged region attracts positively charged Ca+ ions, but also that enzymes in the glycoprotein produce carbonate, in close proximity to the collected Ca+ ions. Even this is known to be incomplete. Different proteins may be used to nucleate (begin) crystal formation to the ones that encourage growth, or that control growth to produce the patterns observed.

Matthewson was introduced to the topic by his research supervisor at Otago, Dr Kate McGrath, who he followed to Vic. While studying the organic formation of rollable LCD screens, Matthewson became frustrated with blemishes that were distorting the formations. After wondering whether proteins existed which could be used to map out and control crystal formation, Dr McGrath introduced him to research on paua that did just that.

Matthewson points out the almost science-fiction potential of future uses of his and others’ research, particularly in electronics. “This glycoprotein, what it does is it builds! And if we want to build stuff, why don’t we get that to build it?”

Benjamin Matthewson holds a BSc(Hons) in physical chemistry from Otago University. He is employed by the MacDiarmid Institute, a nanotechnology research lab in Victoria University.