Buy article online - an online subscription or single-article purchase is required to access this article.
Download citation
Download citation
link to html
Biochemistry, biological crystallography, spectroscopy, solution X-ray scattering and microscopy have been applied to study the molecular basis of the colouration in lobster shell. This article presents a review of progress concentrating on recent results but set in the context of more than 50 years of work. The blue colouration of the carapace of the lobster Homarus gammarus is provided by a multimolecular caroteno­protein, α-crustacyanin. The complex is a 16-mer of five different subunits each binding the carotenoid, asta­xanthin (AXT). A breakthrough in the structural studies came from the determination of the structure of β-crustacyanin (protein subunits A1 with A3 with two shared bound astaxanthins). This was solved by molecular replacement using apocrustacyanin A1 as the search motif. A molecular movie has now been calculated by linear interpolation based on these two `end-point' protein structures, i.e. apocrustacyanin A1 and A1 associated with the two astaxanthins in β-crustacyanin, and is presented with this paper. This movie highlights the structural changes forced upon the carotenoid on complexation. In contrast, the 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. It is suggested here that this loop could be important in complexation of AXT and contributes to the spectral properties. Also presented here is the first observation of single-crystal diffraction of the full `α-­crustacyanin' complex comprising 16 protein subunits and 16 bound AXT molecules (i.e eight β-crustacyanins) at 5 Å resolution. Optimization of crystallization conditions is still necessary as these patterns show multiple crystallite character, however, 10 Å resolution single-crystal diffraction has now been achieved. Provision of the new SRS MPW 10 and SRS MPW 14 beamline robotic systems will greatly assist in the surveying of the many α-crustacyanin crystallization trials that are being made. New solution X-ray scattering (SXS) measurements of β- and α-crustacyanin are also presented. The β-crustacyanin SXS data serve to show how the holo complex fits the SXS curve, whereas the apocrustacyanin A1 homodimer from the crystal data naturally does not. Reconstructions of α-crustacyanin were accomplished from its scattering-profile shape. The most plausible ultrastructure, based on a fourfold symmetry constraint, was found to be a stool with four legs. The latter is compared with published electron micrographs. A detailed crystal structure of α-crustacyanin is now sought in order to relate the full 150 nm bathochromic shift of AXT to that complete molecular structure, compared with the 100 nm achieved by the β-­crustacyanin protein dimer alone. Rare lobster colourations have been brought to attention as a result of this work and are discussed in an appendix.

Supporting information


Graphic Interchange Format (GIF) image
Homarus gammarus crustacyanin


Graphic Interchange Format (GIF) image
Astaxanthin floating into the crustacyanin binding pocket


Graphic Interchange Format (GIF) image
Close up of astaxanthin1 floating into the binding site

Subscribe to Acta Crystallographica Section D: Biological Crystallography

The full text of this article is available to subscribers to the journal.

If you have already registered and are using a computer listed in your registration details, please email for assistance.

Buy online

You may purchase this article in PDF and/or HTML formats. For purchasers in the European Community who do not have a VAT number, VAT will be added at the local rate. Payments to the IUCr are handled by WorldPay, who will accept payment by credit card in several currencies. To purchase the article, please complete the form below (fields marked * are required), and then click on `Continue'.
E-mail address* 
Repeat e-mail address* 
(for error checking) 

Format*   PDF (US $40)
   HTML (US $40)
   PDF+HTML (US $50)
In order for VAT to be shown for your country javascript needs to be enabled.

VAT number 
(non-UK EC countries only) 

Terms and conditions of use
Contact us

Follow Acta Cryst. D
Sign up for e-alerts
Follow Acta Cryst. on Twitter
Follow us on facebook
Sign up for RSS feeds