Tuning C-Phycocyanin Photoactivity via pH-Mediated Assembly–Disassembly

Abstract

Environment-triggered protein conformational changes have garnered wide interest in both fundamental research, for deciphering in vivo acclimatory responses, and practical applications, for designing stimuli-responsive probes. Here, we propose a protein−chromophore regulatory mechanism that allows for manipulation of C-phycocyanin (C-PC) from Spirulina platensis by environmental pH and UV irradiation. Using small-angle X-ray scattering, a pHmediated C-PC assembly−disassembly pathway, from monomers to nonamers, was unraveled. Such flexible protein matrices impart tunability to the embedded tetrapyrroles, whose photochemical behaviors were found to be modulated by protein assembly states. UV irradiation on C-PC triggers pH-dependent singlet oxygen ( 1 O 2 ) generation and conformational changes. Intermolecular photo-crosslinking occurs at pH 5.0 via dityrosine species, which bridges solution-based C-PC oligomers into unprecedented dodecamers and 24-mers. These supramolecular assemblies impart C-PC at pH 5.0, which significantly enhanced 1 O 2 yield, fluorescence, and photostability relative to those at other pH values, a finding that makes C-PC appealing for tumor-targeted photodynamic therapy.

Exploring and strengthening the potential of R-phycocyanin from Nori flakes as a food colourant

“…The native structure of R-PC was preserved in dried Nori flakes, as confirmed by high αhelical content (>50 %). Although (to the best of our knowledge) no previous studies are focusing on the far-UV CD spectra of R-PC, our results are in good agreement with the obtained α-helical content for C-PC from Spirulina and other cyanobacteria (Chen, Liu, MacColl, & Berns, 1983;Chi et al, 2020;Edwards, Hauer, Stack, Eisele, & MacColl, 1997;Li, Gillilan, & Abbaspourrad, 2021).…”

“…However, the main spectral feature of R-PC is still preserved, indicating the absence of complete protein denaturation. A similar observation was made on C-PC from Spirulina, which was not entirely unfolded at pH 3 and 9 (Li et al, 2021;Zhang, Cho, Dadmohammadi, Li, & Abbaspourrad, 2021). Moreover, in contrast to R-PC, the α-helical structure in C-PC is mostly preserved at pH 9 (Li et al, 2021).…”

“…A similar observation was made on C-PC from Spirulina, which was not entirely unfolded at pH 3 and 9 (Li et al, 2021;Zhang, Cho, Dadmohammadi, Li, & Abbaspourrad, 2021). Moreover, in contrast to R-PC, the α-helical structure in C-PC is mostly preserved at pH 9 (Li et al, 2021). Still, C-PC becomes more flexible, and dissociation from hexamers/trimers to monomers was observed at pH 9 (Li et al, 2021).…”

“…The colour of R-PC exhibits good stability in the pH range of 4-8, previously shown for phycocyanin from Spirulina (Li et al, 2021;Yan et al, 2010). The secondary structures (α-helices)…”

Statistical Optimization and Downstream Processing of C‐Phycocyanin from Phormidium valderianum

“…A certain loss was expected, because C‐PC was usually found as αβ ‐trimers and αβ ‐hexamers along with αβ ‐monomers 45–47. After purification with several membranes, filtration with the PVDF membrane, which has a pore size of 0.45 μm, was found to be more efficient as in Fig.…”