Lobster colour change- mystery unravelled

UK researchers announced a first this week when they reported their discovery of how lobsters change colour - the findings could herald new food colourings, dyestuffs and drug delivery mechanisms.

Writing in the journal Proceedings of the National Academy of Science​, scientists from Imperial College London​, University of Manchester, Daresbury Laboratory and Royal Holloway, University of London describe how they have solved the structure of a key part of the lobster shell protein, Beta-Crustacyanin.

Visualising the key subunit of this large molecule allows them to show how structural changes within it can bend the shape of the colour molecule bound to it, Astaxanthin, to make different colours.

Astaxanthin, a carotenoid, has its light-absorption properties altered by the subunit as it undergoes the bathochromic shift. In its free, unbound form it is orange, but when tightly held by Crustacyanins clamp-like protein subunits, it is flattened and becomes blue.

The effect of cooking lobster is to denature the Crustacyanin unit so much that it becomes permanently stuck in the free form, coloured orange.

Dr Naomi Chayen of Imperial College London said: "This could lead to an important new use of Astaxanthin as a drug-delivery mechanism for medicines that are insoluble in water, and give designers of new food colourants or dyestuffs an interesting new capability.​

"It also concludes painstaking research begun by this UK team in 1995, and finally settles a question which has continued to intrigue biologists since Nobel Prize winner George Wald first drew attention to it in 1948."​

The researchers report that in order to gain insight into the mechanism of the molecules that drive the colour change, it is necessary to look at their 3 - dimensional structure, preferably by X-ray crystallography which requires crystals.

Initial separation and isolation work by Dr Peter Zagalsky of Royal Holloway, University of London, yielded a sample of highly pure Crustacyanin which was then handed to crystal grower Dr Naomi Chayen of Imperial College London.

Dr Chayen made use of the unique Microbatch method of growing crystals under oil (of which she is a co-developer), after the classic crystallisation methods repeatedly failed.

According to a statement Chayen almost abandoned the experiments to grow the crystals after two months, but her persistence paid off as the solution she had carefully put to one side finally produced beautiful blue crystals after four months.

Team members at University of Manchester led by Professor John Helliwell used X-ray crystallographic techniques, including innovative use of softer X-rays on the Synchrotron Radiation Source at Daresbury Laboratory with Dr Pierre Rizkallah, to establish the B-Crustacyanin structure in detail. The Manchester Structural Chemistry Laboratory then harnessed the crystal structure models to account for the colour change.