Complete sequence and model for the C1 subunit of the carotenoprotein, crustacyanin, and model for the dimer, beta-crustacyanin, formed from the C1 and A2 subunits with astaxanthin.
The complete sequence has been determined for the C1 subunit of crustacyanin, an astaxanthin-binding protein from the carapace of the lobster Homarus gammarus (L.). The polypeptide, 181 residues long, is similar (38% identity) to the other main subunit, A2 and to plasma retinol-binding protein. The tertiary structure of the C1 subunit has been modelled on that derived for the A2 subunit from the coordinates of retinol-binding protein. Residues lining the putative binding cavities and at the putative carotenoid binding sites of the two subunits are highly conserved. The carotenoid environments are characterized by a preponderance of aromatic and polar residues and the absence of charged side-chains. A tentative model for the dimer, beta-crustacyanin, formed between the two subunits with their associated carotenoid ligands, is discussed. The model is based on the crystal structure of the dimer of bilin-binding protein, a member of the same superfamily. This structure has enabled us to examine mechanisms for the bathochromic spectral shift of the protein-bound carotenoid and to identify likely contact regions between dimers in octameric alpha-crustacyanin.
Keen
J N
JN
Department of Biochemistry and Molecular Biology, University of Leeds, England.
Caceres
I
I
Eliopoulos
E E
EE
Zagalsky
P F
PF
Findlay
J B
JB
D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D002338:Carotenoids / Q000737:chemistry* / Q000378:metabolism; D002352:Carrier Proteins; D055598:Chemical Phenomena; D002627:Chemistry, Physical; D046911:Macromolecular Substances; D008958:Models, Molecular; D008969:Molecular Sequence Data; D008121:Nephropidae / Q000737:chemistry*; D011487:Protein Conformation; D011506:Proteins / Q000737:chemistry*; D024341:Xanthophylls; D019207:beta Carotene / Q000031:analogs & derivatives*
D002352:Carrier Proteins; D046911:Macromolecular Substances; D011506:Proteins; D024341:Xanthophylls; C018494:crustacyanins; D019207:beta Carotene; D002338:Carotenoids; C005948:astaxanthine