Phycobiliproteins: Structural aspects, functional characteristics, and biotechnological perspectives

Abstract

Phycobiliproteins (PBPs) are fluorescent proteins of various colors, including fuchsia, purple-blue and cyan, that allow the capture of light energy in auxiliary photosynthetic complexes called phycobilisomes (PBS). PBPs have several highly preserved structural and physicochemical characteristics. In the PBS context, PBPs function is capture luminous energy in the 450-650 nm range and delivers it to photosystems allowing photosynthesis take place. Besides the energy harvesting function, PBPs also have shown to have multiple biological activities, including antioxidant, antibacterial and antitumours, making them an interesting focus for different biotechnological applications in areas like biomedicine, bioenergy and scientific research. Nowadays, the main sources of PBPs are cyanobacteria and micro and macro algae from the phylum Rhodophyta. Due to the diverse biological activities of PBPs, they have attracted the attention of different industries, such as food, biomedical and cosmetics. This is why a large number of patents related to the production, extraction, purification of PBPs and their application as cosmetics, biopharmaceuticals or diagnostic applications have been generated, looking less ecological impact in the natural prairies of macroalgae and less culture time or higher productivity in cyanobacteria to satisfy the markets and applications that require high amounts of these molecules. In this review, we summarize the main structural characteristics of PBPs, their biosynthesys and biotechnological applications. We also address current trends and future perspectives of the PBPs market.

Keywords: Bioactive molecules; Biotechnology; PBPs; Protein structure.

Graphical abstract

Fig. 1

(a) Molecular structure of chlorophyll a. (b) Absorption spectrum of Chlorophyll a from Agarophyton chilense. (Chlorphyll a molecule created with pymol from PDB:5B66. Absorption spectrum of Chl a made by the authors, unpublished data).

Fig. 2

Structure of Porphyridium purpureum phycobilisome. In pink and light pink PE are shown. In Purple and light purple PC are shown. In turqoise and light turqoise APC are shown. (Phycobilisome image created with pymol from PDB: 6xwk). (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)

Fig. 3

Absorption spectrum of PBPs from rhodophytes. PE spectrum ref . PC spectrum ref . APC spectrum ref

Fig. 4

Structural aligment of α and β subunits of APC, PC, PEC and PE. Green residue shows the cysteine residue which is always chrmoforilated. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)

Fig. 5

Structural level of PBPs. (a) Subunit α, (b) subunit β. (c) heterodimer αβ.

Fig. 6

Structural level of PBPs (a) trimer (αβ)₃ front view. (b) trimer (αβ)₃ side view.

Fig. 7

Structural level of PBPs. (a) trimers (αβ)3 face-to-face, (b) hexamer(αβ)₆ side view. (c) hexamer(αβ)₆ front view.

Fig. 8

PBS rod. In blue α subunits. of PC. In purple β subunits of PC. In magenta α subunits of PE. In fuchsia β subunits of PE. In green PCB and PEB molecules. Figure made with pymol using P. Purpureum PBS structure (PDB id: 6KGX).

Fig. 9

Phycobilins biosynthesis. 2D representantions are based in experimental 3D spatial orientation of phycobilins.