Spectroscopic and molecular docking studies on the interaction of phycocyanobilin with peptide moieties of C-phycocyanin

Abstract The binding of C-phycocyanin (CPC), a light harvesting pigment with phycocyanobilin (PCB), a chromophore is instrumental for the coloration and bioactivity. In this study, structure-mediated color changes of CPC from Spirulina platensis during various enzymatic hydrolysis was investigated based on UV–visible, circular dichroism, infra-red, fluorescence, mass spectrometry, and molecular docking. CPC was hydrolyzed using 7.09 U/mg protein of each enzyme at their optimal hydrolytic conditions for 3 h as follows: papain (pH 6.6, 60 °C), dispase (pH 6.6, 50 °C), and trypsin (pH 7.8, 37 °C). The degree of hydrolysis was in the order of papain (28.4%) > dispase (20.8%) > trypsin (7.3%). The sequence of color degradation rate and total color difference (ΔE) are dispase (82.9% and 40.37), papain (72.4% and 24.70), and trypsin (58.7% and 25.43). The hydrolyzed peptides were of diverse sequence length ranging from 8 to 9 residues (papain), 7–12 residues (dispase), and 9–63 residues (trypsin). Molecular docking studies showed that key amino acid residues in the peptides interacting with chromophore. Amino acid residues such as Arg86, Asp87, Tyr97, Asp152, Phe164, Ala167, and Val171 are crucial in hydrogen bonding interaction. These results indicate that the color properties of CPC might associate with chromopeptide sequences and their non-covalent interactions.