Uncovering the light absorption mechanism of the blue natural colorant allophycocyanin from Arthrospira platensis using molecular dynamics

• Published in: Food chemistry 2025-02, Vol.466, p.141834, Article 141834
• Main Authors: Buecker, Stephan, Sanders, Jeffrey M., Winget, Paul, Leeb, Elena, Grossmann, Lutz, Gibis, Monika, Weiss, Jochen
• Format: Article
• Language: English
• Subjects: Bacterial Proteins - chemistry; Bacterial Proteins - metabolism; Band-shape assumption; Chromophore torsion; Color; Food Coloring Agents - chemistry; Hydrogen-Ion Concentration; Light; Molecular Dynamics Simulation; Phycobiliprotein; Phycocyanin - chemistry; Phycocyanobilin; Protein chromophore interactions; Spirulina - chemistry
• ISSN: 0308-8146; 1873-7072; 1873-7072
• DOI: 10.1016/j.foodchem.2024.141834

Phycobiliproteins of the cyanobacterium Arthrospira platensis, known as Spirulina, are protein-chromophore complexes which are used by the organism to capture light energy. Allophycocyanin and C-phycocyanin are prominent in providing a natural source of blue food coloring. An unresolved issue remains the rapid loss of the native conformation of the pigment, leading to altered color with changing pH. This study investigates color changes on a quantum mechanics scale. A model was established to predict color shifts upon environmental changes, while proposing a mechanism to elucidate pH-dependent chromophore dynamics. On average, the model predicts a hypsochromic shift of 34 nm, in close alignment with the experimentally determined 36 nm. Results show several key non-covalent interactions governing the dynamics of the pyrrole rings of allophycocyanin, particularly influenced by solvents and pH. Particularly noteworthy are the hydrogen bonds with arginine (R 86) and aspartic acid (D 87), contributing to the distinctive optical absorption properties. These findings aid in pigment selection and the targeting of specific phycocyanin regions for stabilization, reducing the dependence on artificial food colors. [Display omitted] •Quantum mechanical evaluation of environmental effects on allophycocyanin color.•Method predicts protein-chromophore dynamics and identifies key interactions.•Reliable results by analyzing a large number of chromophore structures at once.•Hydrogen bonds with R 86, D 87 and the C 16 atom of phycocyanobilin are essential.•Hypsochromic color shift of allophycocyanin from Arthrospira platensis at acidic pH.