ABSTRACT
Biological crystallography, spectroscopy, solution X-ray scattering, and microscopy have all been applied to study the molecular basis of the colouration in lobster shell. This topical review is based on the biological plenary lecture to the BCA Young Crystallographers by the author and which presented a review of progress concentrating on recent results but set in the context of more than 50 years work. In the lobster shell, there is a complex of proteins called α-crustacyanin, which is made of β-crustacyanins, which are made up of different combinations of apoproteins as posttranslationally modied proteins from two genes (A2 and A3 as well as A1, C1 and C2) (see (1) and references therein). In particular, a breakthrough in the structural studies came from the determination of the crystal structures of apocrustacyanin A1 at 1.4 Å resolution (2) and β-crustacyanin (A1 with A3 protein subunits with two, shared, bound astaxanthins) at 3.2 Å resolution (3). The latter (Figure 6.1) was solved by molecular replacement using apocrustacyanin A1 as the search motif. A ‘molecular movie’ has been calculated by linear interpolation based on these two ‘end point’ A1 protein structures, i.e. unbound and bound astaxanthin complex A1 protein structures and was presented (1) as an electronic supplementary deposition within the International Union of Crystallography (IUCr) Journals archive based in Chester, United Kingdom. The movie highlights the structural changes forced upon the carotenoid on complexation with the protein. By contrast, the
6.5 The theoretical chemical basis of the colour shift .............................................................. 134
6.6 Conclusions and future directions ....................................................................................... 136
Acknowledgements ...................................................................................................................... 136
Notes on the contributor .............................................................................................................. 137
References ..................................................................................................................................... 137
protein-binding site remains relatively unchanged in the binding region, but there is a large conformational change occurring in a more remote, surface loop region.
