STRUCTURAL AND FUNCTIONAL CHARACTERISATION OF α-CRUSTACYANIN FROM HOMARUS AMERICANUS

This thesis investigates α-crustacyanin, a carotenoprotein responsible for the dark-blue colouration of the lobster Homarus americanus. Using an integrated approach, which combines X-ray macromolecular crystallography, cryo-electron microscopy (cryo-EM), small-angle X-ray scattering (SAXS), size-exclusion chromatography (SEC), and other biochemical and biophysical techniques, we characterized for the first time the architecture and oligomeric state of α-crustacyanin. Our analysis reveals an elongated assembly of β-crustacyanin heterodimers stabilised by a helical heptatricopeptide repeat protein (HPR). These findings provide an atomic-level description of the protein structure and its role in modulating the spectral properties of its ligand, the chromophore astaxanthin, leading to the characteristic dark-blue colour. Overall, this work elucidates how α-crustacyanin confers the natural blue colour to lobster carapace and establishes a platform to manipulate astaxanthin absorption spectrum for potential applications in bio-inspired materials.